1.1 CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims the benefit of, and priority to, to U.S. Provisional Patent Application No. 63/036,278, filed on June 8, 2020, which is hereby incorporated by reference herein in its entirety.

2 BACKGROUND OF THE TECHNOLOGY

2.1 FIELD OF THE TECHNOLOGY

[0002] The present technology relates to devices for the treatment, prevention and amelioration of respiratory-related disorders. The present technology specifically relates to determining water level in a humidifier for medical devices or apparatus.

2.2 DESCRIPTION OF THE RELATED ART

[0003] The respiratory system of the body facilitates gas exchange. The nose and mouth form the entrance to the airways of a patient. The airways include a series of branching tubes, which become narrower, shorter and more numerous as they penetrate deeper into the lung. The prime function of the lung is gas exchange, allowing oxygen to move from the inhaled air into the venous blood and carbon dioxide to move in the opposite direction. The trachea divides into right and left main bronchi, which further divide eventually into terminal bronchioles. The bronchi make up the conducting airways, and do not take part in gas exchange. Further divisions of the airways lead to the respiratory bronchioles, and eventually to the alveoli. The alveolated region of the lung is where the gas exchange takes place, and is referred to as the respiratory zone. See “ Respiratory Physiology” , by John B. West, Lippincott Williams & Wilkins, 9th edition published 2012.

[0004] A range of respiratory disorders exist. Certain disorders may be characterised by particular events, e.g. apneas, hypopneas, and hyperpneas. Examples of respiratory disorders include Sleep Disordered Breathing (SDB) such as Obstructive Sleep Apnea (OSA), Central Sleep Apnea (CSA), hypopneas and mixed apneas, Cheyne-Stokes Respiration (CSR), respiratory insufficiency, Obesity Hyperventilation Syndrome (OHS), Chronic Obstructive Pulmonary Disease (COPD), Neuromuscular Disease (NMD) and Chest wall disorders.

[0005] Chronic diseases are the leading causes of death and disability worldwide. By 2020 their contribution is expected to rise to 73% of all deaths and 60% of the global burden of disease. This is associated with soaring costs of health care. Chronic diseases are the primary driver of health care costs, accounting for ninety cents (900) of every dollar spent in the U.S. This cost is related to an aging population. In 2015, one out of eight people worldwide was aged 60 years or over. By 2030, it is estimated that one in six people will be aged 60 years or over.

[0006] A range of therapies have been used to treat or ameliorate such conditions. Furthermore, otherwise healthy individuals may take advantage of such therapies to prevent respiratory disorders from arising. However, these have a number of shortcomings.

[0007] Various therapies, such as Continuous Positive Airway Pressure (CPAP) therapy, Non- invasive ventilation (NIV) and Invasive ventilation (IV) have been used to treat one or more of the above respiratory disorders.

[0008] Continuous Positive Airway Pressure (CPAP) therapy has been used to treat Obstructive Sleep Apnea (OSA). The mechanism of action is that continuous positive airway pressure acts as a pneumatic splint and may prevent upper airway occlusion, such as by pushing the soft palate and tongue forward and away from the posterior oropharyngeal wall. Treatment of OSA by CPAP therapy may be voluntary, and hence patients may elect not to comply with therapy if they find devices used to provide such therapy are one or more of: uncomfortable, difficult to use, expensive and aesthetically unappealing.

[0009] Non-invasive ventilation (NIV) provides ventilatory support to a patient through the upper airways to assist the patient breathing and/or maintain adequate oxygen levels in the body by doing some or all of the work of breathing. The ventilatory support is provided via a non-invasive patient interface. NIV has been used to treat CSR and respiratory failure, in forms such as OHS, COPD, NMD and Chest Wall disorders. In some forms, the comfort and effectiveness of these therapies may be improved.

[0010] Invasive ventilation (IV) provides ventilatory support to patients that are no longer able to effectively breathe themselves and may be provided using a tracheostomy tube. In some forms, the comfort and effectiveness of these therapies may be improved.

[0011] These respiratory therapies may be provided by a therapy system or device. A respiratory pressure therapy (RPT) device may be used individually or as part of a system to deliver one or more of a number of therapies described above, such as by operating the device to generate a flow of air for delivery to an interface to the airways. A respiratory therapy system may comprise a Respiratory Pressure Therapy device (RPT device), an air circuit, a humidifier, a patient interface, an oxygen source, and data management. [0012] A patient interface (otherwise referred to as a user interface or mask) may be used to interface respiratory equipment to its wearer, for example by providing a flow of air to an entrance to the airways. The flow of air may be provided via a mask to the nose and/or mouth, a tube to the mouth or a tracheostomy tube to the trachea of a patient. Depending upon the therapy to be applied, the patient interface may form a seal, e.g., with a region of the patient's face, to facilitate the delivery of gas at a pressure at sufficient variance with ambient pressure to effect therapy, e.g., at a positive pressure of about 10 cmH ₂ O relative to ambient pressure. For other forms of therapy, such as the delivery of oxygen, the patient interface may not include a seal sufficient to facilitate delivery to the airways of a supply of gas at a positive pressure of about 10 cmH ₂ O.

[0013] Air pressure generators are known in a range of applications, e.g. industrial-scale ventilation systems. However, air pressure generators for medical applications have particular requirements not fulfilled by more generalised air pressure generators, such as the reliability, size and weight requirements of medical devices. In addition, even devices designed for medical treatment may suffer from shortcomings, pertaining to one or more of: comfort, noise, ease of use, efficacy, size, weight, manufacturability, cost, and reliability.

[0014] Delivery of a flow of air without humidification may cause drying of airways. The use of a humidifier with an RPT device and the patient interface produces humidified gas that minimizes drying of the nasal mucosa and increases patient airway comfort. In addition, in cooler climates, warm air applied generally to the face area in and about the patient interface is more comfortable than cold air. However, one issue with a humidifier is maintaining the water level, as an underfilled or overfilled reservoir may affect operation of the RPT device. Although current reservoirs have a visual fill indicator, the fill indicator requires removing the reservoir to determine the water level in the reservoir. Thus, the RPT device cannot be operating while the water level is determined.

[0015] Thus, there is a need for a process to determine water level in a humidifier reservoir while the RPT device is operating. There is a further need for a system that incorporates existing components or an RPT device for acoustic determination of a water level in a humidifier. There is also a need for an RPT device with a humidifier that allows adjustment of the humidifier operation depending on a detected water level.

3 BRIEF SUMMARY OF THE TECHNOLOGY

[0016] The present technology is directed towards using an acoustic sensor to detect the water level of a tank for a humidifier in an RPT device. The automatic detection of the water level allows the alerting of a user that water levels are low that may adversely affect the operation of the RPT device.

[0017] One disclosed example is a respiratory therapy device including a sound generator operable to produce acoustic signals. The device includes a flow generator operable to provide a flow of air to a patient interface. A humidifier including a water reservoir is operable to humidify the air provided to the interface. An acoustic sensor is operable to sense acoustic signals from the sound generator that have travelled through the humidifier. A controller is coupled to the acoustic sensor. The controller is operable to determine a water level in the reservoir from the sensed acoustic signal.

[0018] In implementations of the example device is an embodiment where the device includes a display showing the water level in the reservoir. In implementations the device includes an alarm triggered if the water level of the reservoir is below a pre-determined value. In implementations, the controller compares the determined water level with an expected water level value. In implementations, the expected water level value is determined from at least one of: one or more past determined water levels, one or more past rate of change in determined water levels, a humidity setting of the respiratory therapy device, a therapy setting of the respiratory therapy device, the type of patient interface, or ambient conditions in the vicinity of the respiratory therapy device. In implementations, the controller provides an alert of a mechanical fault of the respiratory therapy device when the water level deviates from the expected water level. In implementations, the controller provides an alert of a leak event relating to a patient using the respiratory therapy device when the water level deviates from the expected water level. In implementations, the acoustic signal is processed with cepstrum analysis, and wherein a cepstrum amplitude is compared with a baseline amplitude corresponding with a water level value. In implementations, the acoustic signal is processed with spectrum analysis, and where a frequency spectrum is compared with a baseline frequency spectrum corresponding with a water level value. In implementations, the sound generator is a motor of the flow generator. In implementations, the controller filters out other sounds detected by the acoustic sensor. Another implementation is where the acoustic sensor detects inspiration and expiration sounds from a patient breathing air from the patient interface, and where the controller samples the acoustic signals generated by the sound generator between the inspiration and expiration sounds from the patient. In implementations, the controller filters out breathing noises from a patient breathing air from the patient interface detected by the acoustic sensor. In implementations, the flow generator includes a motor, wherein the speed of the motor is input to the controller to filter out motor noise detected by the acoustic sensor. In implementations, the reservoir is physically located between the sound generator and the acoustic sensor, wherein an acoustic pathway is defined between the sound generator and the acoustic sensor. In implementations, the sound generator is a speaker positioned on or within the reservoir. In implementations, the speaker emits a waveform including one or more of a frequency modulated continuous wave (FMCW), frequency hopping range gating (FHRG), continuous wave (CW), pulsed continuous wave, narrow band, or ultra wide band (UWB) such as a white noise sensing signal. The waveform may additionally or alternatively include a coded sound such as amplitude-shift keying (ASK), frequency-shift keying (FSK), or phase- shift keying (PSK), etc. The speaker may also be or comprise a transducer such as a buzzer. In implementations, the controller activates a water source to supply water to the reservoir in response to the determined water level being below a pre-determined low level. In implementations, the device includes an electronic display, and wherein the controller is operable to cause a notification to be communicated via the electronic display, the notification indicating the determined water level in the reservoir and/or a recommendation to add water to the water reservoir. In implementations, the electronic display is an electronic display of the respiratory therapy device or an electronic device operable to communicate with the controller of the respiratory therapy device. In implementations, the humidifier includes a heating element for heating the water in the reservoir, and wherein the controller is operable to adjust the heating element in response to the determined water level. In implementations, the sensed acoustic signal is a reflected acoustic signal from a sound of the sound generator reflected by the reservoir.

[0019] Another disclosed example is a method of determining a water level in a reservoir of a humidifier in a respiratory therapy system. The respiratory therapy system includes a flow generator providing air flow to a patient interface. An acoustic signal is generated from a sound generator. The acoustic signal from the generated acoustic signal that have travelled through the reservoir is sensed via an acoustic sensor. The water level in the reservoir is determined based on the sensed acoustic signal via a controller.

[0020] In implementations, displaying the water level in the reservoir is displayed on a display. In implementations, the method further includes triggering an alarm if the water level of the reservoir is below a pre-determined value. In implementations, the method further includes comparing the determined water level with an expected water level value. In implementations, the expected water level value is determined from at least one of: one or more past determined water levels, one or more past rate of change in determined water levels, a humidity setting of the respiratory therapy device, a therapy setting of the respiratory therapy device, the type of patient interface, or ambient conditions in the vicinity of the respiratory therapy device. In implementations, the method further includes providing an alert of a mechanical fault of the respiratory therapy device when the water level deviates from the expected water level. In implementations, the method further includes providing an alert of a leak event relating to a patient using the respiratory therapy device when the water level deviates from the expected water level. In implementations, the sensed acoustic signal is processed with cepstrum analysis, and wherein a cepstrum amplitude is compared with a baseline amplitude corresponding with a water level value. In implementations, the acoustic signal is processed with spectrum analysis, and where a frequency spectrum is compared with a baseline frequency spectrum corresponding with a water level value. In implementations, the sound generator is a motor of the flow generator. In implementations, the method further includes filtering out other sounds detected by the acoustic sensor. In implementations, the method further includes detecting inspiration and expiration sounds from a patient breathing air from the patient interface; and sampling the sensed acoustic signals generated by the sound generator between the inspiration and expiration sounds from the patient. In implementations, the method further includes filtering out breathing noises from a patient breathing air from the patient interface detected by the acoustic sensor. In implementations, the flow generator includes a motor. The speed of the motor is input to the controller to filter out motor noise detected by the acoustic sensor. In implementations, the reservoir is physically located between the sound generator and the acoustic sensor, and where an acoustic pathway is defined between the sound generator and the acoustic sensor. In implementations, the sound generator is a speaker positioned on or within the reservoir. In implementations, the speaker emits a waveform including one or more of a frequency modulated continuous wave (FMCW), frequency hopping range gating (FHRG), continuous wave (CW), pulsed continuous wave, narrow band, or ultra wide band (UWB). In implementations, the method further includes activating a water source to supply water to the reservoir in response to the determined water level being below a pre-determined low level. In implementations, the method further includes causing a notification to be communicated via an electronic display. The notification indicates the determined water level in the reservoir and/or a recommendation to add water to the water reservoir. In implementations, the electronic display is an electronic display of the respiratory therapy device or an electronic device operable to communicate with the controller of the respiratory therapy device. In implementations, the method further includes adjusting a heating element of the reservoir heating the water in the reservoir in response to the determined water level. In implementations, the sensed acoustic signal is a reflected acoustic signal from a sound of the sound generator reflected by the reservoir.

[0021] Another disclosed example is a computer program product comprising instructions which, when executed by a computer, cause the computer to carry out a method of generating an acoustic signal from a sound generator. The method also includes sensing the acoustic signal from the generated acoustic signal that has travelled through the reservoir via an acoustic sensor. The method also includes determining the water level in the reservoir based on the sensed acoustic signal.

[0022] In implementations, the method includes displaying the water level in the reservoir on a display. In implementations, the method further includes triggering an alarm if the water level of the reservoir is below a pre-determined value. In implementations, the method further includes comparing the determined water level with an expected water level value. In implementations, the expected water level value is determined from at least one of: one or more past determined water levels, one or more past rate of change in determined water levels, a humidity setting of the respiratory therapy device, a therapy setting of the respiratory therapy device, the type of patient interface, or ambient conditions in the vicinity of the respiratory therapy device. In implementations, the method further includes providing an alert of a mechanical fault of the respiratory therapy device when the water level deviates from the expected water level. In implementations, the method further includes providing an alert of a leak event relating to a patient using the respiratory therapy device when the water level deviates from the expected water level. In implementations, the sensed acoustic signal is processed with cepstrum analysis, and where a cepstrum amplitude is compared with a baseline amplitude corresponding with a water level value. In implementations, the acoustic signal is processed with spectrum analysis, and where a frequency spectrum is compared with a baseline frequency spectrum corresponding with a water level value. In implementations, the sound generator is a motor of the flow generator. In implementations, the method includes filtering out other sounds detected by the acoustic sensor. In implementations, the method further includes detecting inspiration and expiration sounds from a patient breathing air from the patient interface. The method also includes sampling the sensed acoustic signals generated by the sound generator between the inspiration and expiration sounds from the patient. In implementations, the method further includes filtering out breathing noises from a patient breathing air from the patient interface detected by the acoustic sensor. In implementations, the flow generator includes a motor, and the speed of the motor is input to the controller to filter out motor noise detected by the acoustic sensor. In implementations, the reservoir is physically located between the sound generator and the acoustic sensor, and where an acoustic pathway is defined between the sound generator and the acoustic sensor. In implementations, the sound generator is a speaker positioned on or within the reservoir. In implementations, the speaker emits a waveform including one or more of a frequency modulated continuous wave (FMCW), frequency hopping range gating (FHRG), continuous wave (CW), pulsed continuous wave, narrow band, or ultra wide band (UWB). In implementations, the method further includes activating a water source to supply water to the reservoir in response to the determined water level being below a pre-determined low level. In implementations, the method further includes causing a notification to be communicated via an electronic display, the notification indicating the determined water level in the reservoir and/or a recommendation to add water to the water reservoir. In implementations, the electronic display is an electronic display of the respiratory therapy device or an electronic device operable to communicate with the controller of the respiratory therapy device. In implementations, the method further includes adjusting a heating element of the reservoir heating the water in the reservoir in response to the determined water level. In implementations, the sensed acoustic signal is a reflected acoustic signal from a sound of the sound generator reflected by the reservoir.

[0023] The methods, systems, devices and apparatus described herein can provide improved functioning in a processor, such as of a processor of a specific purpose computer, respiratory monitor and/or a respiratory therapy apparatus. Moreover, the described methods, systems, devices and apparatus can provide improvements in the technological field of automated management, monitoring and/or treatment of respiratory conditions, including, for example, sleep disordered breathing.

[0024] Of course, portions of the aspects may form sub-aspects of the present technology. Also, various ones of the sub-aspects and/or aspects may be combined in various manners and also constitute additional aspects or sub-aspects of the present technology.

[0025] Other features of the technology will be apparent from consideration of the information contained in the following detailed description, abstract, drawings and claims.

4 BRIEF DESCRIPTION OF THE DRAWINGS

[0026] The present technology is illustrated by way of example, and not by way of limitation, in the figures of the accompanying drawings, in which like reference numerals refer to similar elements including:

[0027] FIG. 1A shows a system including a patient 1000 wearing a patient interface 3000, in the form of nasal pillows, receiving a supply of air at positive pressure from a respiratory pressure therapy (RPT) device 4000. In this example, the respiratory pressure therapy device may include a PAP device, a non-invasive ventilation (NIV) device, or an adaptive support ventilation (ASV) device. Of course, other devices may also perform the functions of the RPT device 4000 described herein. Air from the RPT device 4000 is humidified in a humidifier 5000, and passes along an air circuit 4170 to the patient 1000. A bed partner 1100 is also shown. The patient 1000 is sleeping in a supine sleeping position.

[0028] FIG. IB shows a system including a patient 1000 wearing a patient interface 3000, in the form of a nasal mask, receiving a supply of air at positive pressure from an RPT device 4000. Air from the RPT device is humidified in a humidifier 5000, and passes along an air circuit 4170 to the patient 1000.

[0029] FIG. 1C shows a system including a patient 1000 wearing a patient interface 3000, in the form of a full-face mask, receiving a supply of air at positive pressure from an RPT device 4000. Air from the RPT device is humidified in a humidifier 5000, and passes along an air circuit 4170 to the patient 1000. The patient is sleeping in a side sleeping position.

[0030] FIG. 2 shows an overview of a human respiratory system including the nasal and oral cavities, the larynx, vocal folds, oesophagus, trachea, bronchus, lung, alveolar sacs, heart and diaphragm.

[0031] FIG. 3 shows a patient interface in the form of a nasal mask in accordance with one form of the present technology.

[0032] FIG. 4A shows an RPT device in accordance with one form of the present technology. [0033] FIG. 4B is a schematic diagram of the pneumatic path of an RPT device in accordance with one form of the present technology. The directions of upstream and downstream are indicated with reference to the flow generator (otherwise referred to as a blower) and the patient interface. The blower is defined to be upstream of the patient interface and the patient interface is defined to be downstream of the blower, regardless of the actual flow direction at any particular moment. Items which are located within the pneumatic path between the blower and the patient interface are downstream of the blower and upstream of the patient interface. [0034] FIG. 4C is a schematic diagram of the electrical components of an RPT device in accordance with one form of the present technology.

[0035] FIG. 4D is a schematic diagram of the algorithms implemented in an RPT device in accordance with one form of the present technology.

[0036] FIG. 4E is a flow chart illustrating a method carried out by the therapy engine module of Fig. 4D in accordance with one form of the present technology. [0037] FIG. 5A shows an isometric view of a humidifier in accordance with one form of the present technology.

[0038] FIG. 5B shows an isometric view of a humidifier in accordance with one form of the present technology, showing a humidifier reservoir 5110 removed from the humidifier reservoir dock 5130.

[0039] FIG. 6 is a schematic view of a respiratory therapy system including the humidifier, sound generator, and acoustic sensor in accordance with one aspect of the present technology. [0040] FIG. 7A is a graph showing the noise spectrum of acoustic signals for different water levels of a humidifier reservoir;

[0041] FIG. 7B is a graph showing the results of cepstrum analysis of acoustic signals for different water levels of a humidifier reservoir; and

[0042] FIG. 8 is a flow chart illustrating a method of determining the water level in the reservoir of an RPT system in accordance with one aspect of the present technology.

5 DETAILED DESCRIPTION OF EXAMPLES OF THE TECHNOLOGY

[0043] Before the present technology is described in further detail, it is to be understood that the technology is not limited to the particular examples described herein, which may vary. It is also to be understood that the terminology used in this disclosure is for the purpose of describing only the particular examples discussed herein, and is not intended to be limiting. [0044] The following description is provided in relation to various examples which may share one or more common characteristics and/or features. It is to be understood that one or more features of any one example may be combinable with one or more features of another example or other examples. In addition, any single feature or combination of features in any of the examples may constitute a further example.

[0045] The present disclosure relates to a system

5.1 THERAPY

[0046] In one form, the present technology comprises a method for treating a respiratory disorder comprising the step of applying positive pressure to the entrance of the airways of a patient 1000 in FIGs. 1 A-1C. In certain examples of the present technology, a supply of air at positive pressure is provided to the nasal passages of the patient via one or both nares. In certain examples of the present technology, mouth breathing is limited, restricted or prevented. 5.2 TREATMENT SYSTEMS

[0047] In one form, the present technology comprises an apparatus or device for treating a respiratory disorder. The apparatus or device may comprise a respiratory pressure therapy (RPT) device 4000 for supplying pressurised air to the patient 1000 via an air circuit 4170 to a patient interface 3000 or 3800.

5.3 PATIENT INTERFACE

[0048] A non-invasive patient interface 3000 in accordance with one aspect of the present technology comprises the following functional aspects: a seal-forming structure 3100, a plenum chamber 3200, a positioning and stabilising structure 3300, a vent 3400, one form of connection port 3600 for connection to air circuit 4170, and a forehead support 3700. In some forms a functional aspect may be provided by one or more physical components. In some forms, one physical component may provide one or more functional aspects. In use the seal forming structure 3100 is arranged to surround an entrance to the airways of the patient so as to facilitate the supply of air at positive pressure to the airways.

[0049] An unsealed patient interface 3800, in the form of a nasal cannula, includes nasal prongs 3810a, 3810b which can deliver air to respective nares of the patient 1000. Such nasal prongs do not generally form a seal with the inner or outer skin surface of the nares. The air to the nasal prongs may be delivered by one or more air supply lumens 3820a, 3820b that are coupled with the nasal cannula 3800. The lumens 3820a, 3820b lead from the nasal cannula 3800 lead to an RPT device that generates the flow of air at high flow rates. The “vent” at the unsealed patient interface 3800, through which excess airflow escapes to ambient, is the passage between the end of the prongs 3810a and 3810b of the cannula 3800 via the patient’s nares to atmosphere.

[0050] In one form of the present technology, a seal-forming structure 3100 provides a target seal-forming surface region, and may additionally provide a cushioning function. The target seal -forming region is a region on the seal-forming structure 3100 where sealing may occur. The region where sealing actually occurs- the actual sealing surface- may change within a given treatment session, from day to day, and from patient to patient, depending on a range of factors including for example, where the patient interface was placed on the face, tension in the positioning and stabilising structure and the shape of a patient’s face.

[0051] The plenum chamber 3200 has a perimeter that is shaped to be complementary to the surface contour of the face of an average person in the region where a seal will form in use. In use, a marginal edge of the plenum chamber 3200 is positioned in close proximity to an adjacent surface of the face. Actual contact with the face is provided by the seal-forming structure 3100. The seal-forming structure 3100 may extend in use about the entire perimeter of the plenum chamber 3200. In some forms, the plenum chamber 3200 and the seal-forming structure 3100 are formed from a single homogeneous piece of material. Alternatively, an acoustic generator may be formed as a part of, or through a shell of, the plenum chamber 3200. [0052] The seal-forming structure 3100 of the patient interface 3000 of the present technology may be held in sealing position in use by the positioning and stabilising structure 3300.

[0053] In one form, the patient interface 3000 includes a vent 3400 constructed and arranged to allow for the washout of exhaled gases, e.g. carbon dioxide. In certain forms the vent 3400 is configured to allow a continuous vent flow from an interior of the plenum chamber 3200 to ambient whilst the pressure within the plenum chamber is positive with respect to ambient. The vent 3400 is configured such that the vent flow rate has a magnitude sufficient to reduce rebreathing of exhaled C02 by the patient while maintaining the therapeutic pressure in the plenum chamber in use. One form of vent 3400 in accordance with the present technology comprises a plurality of holes, for example, about 20 to about 80 holes, or about 40 to about 60 holes, or about 45 to about 55 holes. The vent 3400 may be located in the plenum chamber 3200. Alternatively, the vent 3400 is located in a decoupling structure, e.g., a swivel.

[0054] Connection port 3600 allows for connection to the air circuit 4170, and may optionally include an integrated acoustic generator.

5.4 RPT DEVICE

[0055] An RPT device 4000 in accordance with one aspect of the present technology comprises mechanical, pneumatic, and/or electrical components and is configured to execute one or more algorithms 4300, such as any of the methods, in whole or in part, described herein. The RPT device 4000 may be configured to generate a flow of air for delivery to a patient’s airways, such as to treat one or more of the respiratory conditions described elsewhere in the present document.

[0056] In one form, the RPT device 4000 is constructed and arranged to be capable of delivering a flow of air in a range of -20 L/min to +150 L/min while maintaining a positive pressure of at least 6 cmH ₂ O, or at least lOcmH ₂ O, or at least 20 cmH ₂ O.

[0057] The RPT device 4000 may have an external housing 4010, formed in two parts, an upper portion 4012 and a lower portion 4014. Furthermore, the external housing 4010 may include one or more panel(s) 4015. The RPT device 4000 comprises a chassis 4016 that supports one or more internal components of the RPT device 4000. The RPT device 4000 may include a handle 4018.

[0058] The pneumatic path of the RPT device 4000 may comprise one or more air path items, e.g., an inlet air filter 4112, an inlet muffler 4122, a flow generator 4140 capable of supplying air at positive pressure (e.g., a blower 4142), an outlet muffler 4124 and one or more transducers 4270, such as pressure sensors 4272 and flow rate sensors 4274.

[0059] One or more of the air path items may be located within a removable unitary structure which will be referred to as a pneumatic block 4020. The pneumatic block 4020 may be located within the external housing 4010. In one form a pneumatic block 4020 is supported by, or formed as part of the chassis 4016.

[0060] The RPT device 4000 may have an electrical power supply 4210, one or more input devices 4220, a central controller 4230, a therapy device controller 4240, a flow generator 4140, one or more protection circuits 4250, memory 4260, transducers 4270, data communication interface 4280 and one or more output devices 4290. Electrical components 4200 may be mounted on a single Printed Circuit Board Assembly (PCBA) 4202. In an alternative form, the RPT device 4000 may include more than one PCBA 4202.

[0061] An RPT device may comprise one or more of the following components in an integral unit. In an alternative form, one or more of the following components may be located as respective separate units.

[0062] An RPT device in accordance with one form of the present technology may include an air filter 4110, or a plurality of air filters 4110.

[0063] In one form, an inlet air filter 4112 is located at the beginning of the pneumatic path upstream of the flow generator 4140.

[0064] In one form, an outlet air filter 4114, for example an antibacterial filter, is located between an outlet of the pneumatic block 4020 and a patient interface 3000 or 3800.

[0065] An RPT device in accordance with one form of the present technology may include a muffler 4120, or a plurality of mufflers 4120.

[0066] In one form of the present technology, an inlet muffler 4122 is located in the pneumatic path upstream of the flow generator 4140.

[0067] In one form of the present technology, an outlet muffler 4124 is located in the pneumatic path between the flow generator 4140 and a patient interface 3000 or 3800.

[0068] In one form of the present technology, the flow generator 4140 for producing a flow, or a supply, of air at positive pressure is a controllable blower 4142. For example, the blower 4142 may include a brushless DC motor 4144 with one or more impellers. The impellers may be located in a volute. The blower 4142 may be capable of delivering a supply of air, for example at a rate of up to about 120 litres/minute, at a positive pressure in a range from about 4 cmThO to about 20 cmThO, or in other forms up to about 30 cmThO. The blower may be as described in any one of the following patents or patent applications the contents of which are incorporated herein by reference in their entirety: U.S. Patent No. 7,866,944; U.S. Patent No. 8,638,014; U.S. Patent No. 8,636,479; and PCT Patent Application Publication No. WO 2013/020167.

[0069] The flow generator 4140 is under the control of the therapy device controller 4240. In other forms, the flow generator 4140 may be a piston-driven pump, a pressure regulator connected to a high pressure source (e.g. compressed air reservoir), or a bellows.

[0070] Transducers may be internal of the RPT device 4000, or external of the RPT device 4000. External transducers may be located for example on or form part of the air circuit, e.g., the patient interface. External transducers may be in the form of non-contact sensors such as a Doppler radar movement sensor that transmit or transfer data to the RPT device 4000.

[0071] In one form of the present technology, one or more transducers 4270 are located upstream and/or downstream of the flow generator 4140. The one or more transducers 4270 may be constructed and arranged to generate signals representing properties of the flow of air such as a flow rate, a pressure or a temperature at that point in the pneumatic path.

[0072] In one form of the present technology, one or more transducers 4270 may be located proximate to the patient interface 3000 or 3800. In one form, a signal from a transducer 4270 may be filtered, such as by low-pass, high-pass or band-pass filtering.

[0073] A flow rate sensor 4274 in accordance with the present technology may be based on a differential pressure transducer, for example, an SDP600 Series differential pressure transducer from SENSIRION. In one form, a signal representing a flow rate from the flow rate sensor 4274 is received by the central controller 4230. Examples of flow rate sensors (such as, for example, the flow rate sensor 4274) are described in U.S. Patent No. US 10,328,219 B2, which is hereby incorporated by reference herein in its entirety.

[0074] A pressure sensor 4272 in accordance with the present technology is located in fluid communication with the pneumatic path. An example of a suitable pressure sensor is a transducer from the HONEYWELL ASDX series. An alternative suitable pressure sensor is a transducer from the NPA Series from GENERAL ELECTRIC. In one form, a signal from the pressure sensor 4272 is received by the central controller 4230.

[0075] In one form of the present technology a motor speed transducer 4276 is used to determine a rotational velocity of the motor 4144 and/or the blower 4142. A motor speed signal from the motor speed transducer 4276 may be provided to the therapy device controller 4240. The motor speed transducer 4276 may, for example, be a speed sensor, such as a Hall effect sensor.

[0076] In one form of the present technology, an anti-spill back valve 4160 is located between the humidifier 5000 and the pneumatic block 4020. The anti-spill back valve is constructed and arranged to reduce the risk that water will flow upstream from the humidifier 5000, for example to the motor 4144.

[0077] A power supply 4210 may be located internal or external of the external housing 4010 of the RPT device 4000. In one form of the present technology, power supply 4210 provides electrical power to the RPT device 4000 only. In another form of the present technology, power supply 4210 provides electrical power to both RPT device 4000 and humidifier 5000.

[0078] In one form of the present technology, an RPT device 4000 includes one or more input devices 4220 in the form of buttons, switches or dials to allow a person to interact with the device. The buttons, switches or dials may be physical devices, or software devices accessible via a touch screen. The buttons, switches or dials may, in one form, be physically connected to the external housing 4010, or may, in another form, be in wireless communication with a receiver that is in electrical connection to the central controller 4230.

[0079] In one form, the input device 4220 may be constructed and arranged to allow a person to select a value and/or a menu option.

[0080] Internal sensors such as the flow rate sensor 4274, a pressure sensor 4272, and a motor speed transducer 4276 may be coupled to the central controller 4230 in FIG. 4C. An optional internal audio/acoustic sensor 4278 may be embedded in the interface 3000 in FIG. 1 to detect specific patient air sounds or other sounds relating to the components of the RPT device 4000. An optional external audio sensor 4279 such as a microphone may be located on the exterior of the RPT device 4000, the interface 3000, or the humidifier 5000 to collect additional audio data. Additional sensors such as a heart rate sensor, an ECG sensor (providing cardiac fiducial parameters, of which peaks could be processed to estimate heart rate, detect arrhythmias and so forth), a pulse oximeter (Sp02) sensor (providing heart rate, oxygen saturation, and potential an estimate of blood pressure from pulse transit time), a blood pressure sensor, a room- temperature sensor, a contact or non-contact body temperature sensor, a room humidity sensor, a proximity sensor, a gesture sensor, a touch sensor, a gas sensor, an air quality sensor, a particulate sensor, an accelerometer, a gyroscope, a tilt sensor, other acoustic sensors such as passive or active SONAR (as described in, for example, WO 2018/050913 and WO 2020/104465, each of which is hereby incorporated by reference herein in its entirety), an ultrasonic sensor, a radio frequency sensor, an accelerometer, a light intensity sensor, a LIDAR sensor, an infrared sensor (passive, transmissive, or reflective), carbon dioxide sensor, a carbon monoxide sensor, or a chemical sensor, may be connected to the central controller 4230 via an external port. Data from such additional sensors may also be collected by the central controller 4230. Data from the sensors 4272, 4274, 4276, 4278, and 4279 may be collected by central controller 4230 on a periodic basis. Such data generally relates to the operational state of the RPT device 4000 and the humidifier 5000.

[0081] In one form of the present technology, the central controller 4230 is one or a plurality of processors suitable to control an RPT device 4000. Suitable processors may include an x86 INTEL processor, a processor based on ARM® Cortex®-M processor from ARM Holdings such as an STM32 series microcontroller from ST MICROELECTRONICS. In certain alternative forms of the present technology, a 32-bit RISC CPU, such as an STR9 series microcontroller from ST MICROELECTRONICS or a 16-bit RISC CPU such as a processor from the MSP430 family of microcontrollers, manufactured by TEXAS INSTRUMENTS may also be suitable.

[0082] In one form of the present technology, the central controller 4230 is a dedicated electronic circuit. In one form, the central controller 4230 is an application-specific integrated circuit. In another form, the central controller 4230 comprises discrete electronic components. [0083] The central controller 4230 may be configured to receive input signal(s) from one or more transducers 4270, one or more input devices 4220, and the humidifier 5000. The central controller 4230 may be configured to provide output signal(s) to one or more of an output device 4290, a therapy device controller 4240, a data communication interface 4280, and the humidifier 5000.

[0084] The controller 4230 may collect the data at different rates. For example, during normal use, the data may be collected at a low-resolution rate. As will be explained, a triggering event may cause the controller 4230 to start collecting the data at a different collection rate, such as at a higher resolution rate for collecting more data and/or additional types of data in a comparative time period than the low-resolution rate for more detailed analysis of the patient 1000. In this example, the central controller 4230 encodes such data from the sensors in a proprietary data format. The data may also be coded in a standardized data format.

[0085] In some forms of the present technology, the central controller 4230 is configured to implement the one or more methodologies described herein, such as the one or more algorithms 4300 expressed as computer programs stored in a non-transitory computer readable storage medium, such as memory 4260. In some forms of the present technology, the central controller 4230 may be integrated with an RPT device 4000. However, in some forms of the present technology, some methodologies may be performed by a remotely located device. For example, the remotely located device may determine control settings for a ventilator or detect respiratory related events by analysis of stored data such as from any of the sensors described herein. As explained above, all data and operations for external sources or the central controller 4230 are generally proprietary to the manufacturer of the RPT device 4000. Thus, the data from the sensors and any other additional operational data is not generally accessible by any other device.

[0086] The RPT device 4000 may include a clock 4232 that is connected to the central controller 4230.

[0087] In one form of the present technology, therapy device controller 4240 is a therapy control module 4330 that forms part of the algorithms 4300 executed by the central controller 4230 as shown in FIG. 4D. In one form of the present technology, therapy device controller 4240 is a dedicated motor control integrated circuit. For example, in one form a MC33035 brushless DC motor controller, manufactured by ON SEMI is used.

[0088] The one or more protection circuits 4250 in accordance with the present technology may comprise an electrical protection circuit, a temperature and/or pressure safety circuit. [0089] In accordance with one form of the present technology the RPT device 4000 includes memory 4260, e.g., non-volatile memory. In some forms, memory 4260 may include battery powered static RAM. In some forms, memory 4260 may include volatile RAM. The memory 4260 may be located on the PCBA 4202. The memory 4260 may be in the form of EEPROM, or NAND flash. Additionally, or alternatively, RPT device 4000 includes a removable form of memory 4260, for example a memory card made in accordance with the Secure Digital (SD) standard. In one form of the present technology, the memory 4260 acts as a non-transitory computer readable storage medium on which is stored computer program instructions expressing the one or more methodologies described herein, such as the one or more algorithms 4300.

[0090] In one form of the present technology, a data communication interface 4280 is provided, and is connected to the central controller 4230. Data communication interface 4280 may be connectable to a remote external communication network 4282 and/or a local external communication network 4284. The remote external communication network 4282 may be connectable to a remote external device 4286. The local external communication network 4284 may be connectable to a local external device 4288. [0091] In one form, data communication interface 4280 is part of the central controller 4230. In another form, data communication interface 4280 is separate from the central controller 4230, and may comprise an integrated circuit or a processor. In one form, remote external communication network 4282 is the Internet. The data communication interface 4280 may use wired communication (e.g. via Ethernet, or optical fibre) or a wireless protocol (e.g. CDMA, GSM, LTE) to connect to the Internet. In one form, local external communication network 4284 utilises one or more communication standards, such as Bluetooth, or a consumer infrared protocol.

[0092] In one form, remote external device 4286 is one or more computers, for example a cluster of networked computers. In one form, remote external device 4286 may be virtual computers, rather than physical computers. In either case, such a remote external device 4286 may be accessible to an appropriately authorised person such as a clinician. The local external device 4288 may be a personal computer, mobile phone, tablet or remote control.

[0093] An output device 4290 in accordance with the present technology may take the form of one or more of a visual, audio and haptic unit. A visual display may be a Liquid Crystal Display (LCD) or Light Emitting Diode (LED) display.

[0094] A display driver 4292 receives as an input the characters, symbols, or images intended for display on the display 4294, and converts them to commands that cause the display 4294 to display those characters, symbols, or images.

[0095] A display 4294 is configured to visually display characters, symbols, or images in response to commands received from the display driver 4292. For example, the display 4294 may be an eight-segment display, in which case the display driver 4292 converts each character or symbol, such as the figure “0”, to eight logical signals indicating whether the eight respective segments are to be activated to display a particular character or symbol.

[0096] As mentioned above, in some forms of the present technology, the central controller 4230 may be configured to implement one or more algorithms 4300 in FIG. 4D expressed as computer programs stored in a non-transitory computer readable storage medium, such as memory 4260. The algorithms 4300 are generally grouped into groups referred to as modules. [0097] A pre-processing module 4310 in accordance with one form of the present technology receives as an input a signal from a transducer 4270, for example flow rate sensor 4274, or pressure sensor 4272, or audio/acoustic sensors 4278 and 4279, and performs one or more process steps to calculate one or more output values that will be used as an input to another module, for example a therapy engine module 4320. The pre-processing module 4310 may include routines such as an interface pressure estimation routine 4312, a vent flow rate estimation routine 4314, a leak flow rate estimation routine 4316, and a respiratory flow rate estimation routine 4318. The therapy engine module 4320 may include different routines for determining various parameters such as a phase determination routine 4321, a waveform determination routine 4322, a ventilation determination routine 4323, a flow limitation determination routine 4324, an apnea/hypopnea determination routine 4325, a snore determination routine 4326, an airway patency determination routine 4327, a target ventilation determination routine 4328, and a therapy parameter determination routine 4329. A fault condition detection module 4340 provides detection of faults in the operation of the RPT device 4000.

5.5 AIR CIRCUIT

[0098] An air circuit 4170 in accordance with an aspect of the present technology is a conduit or a tube constructed and arranged to allow, in use, a flow of air to travel between two components such as RPT device 4000 and the patient interface 3000 or 3800.

[0099] In particular, the air circuit 4170 may be in fluid connection with the outlet of the pneumatic block 4020 and the patient interface. The air circuit may be referred to as an air delivery tube. In some cases there may be separate limbs of the circuit for inhalation and exhalation. In other cases a single limb is used.

[0100] In some forms, the air circuit 4170 may comprise one or more heating elements configured to heat air in the air circuit, for example to maintain or raise the temperature of the air. The heating element may be in a form of a heated wire circuit, and may comprise one or more transducers, such as temperature sensors. In one form, the heated wire circuit may be helically wound around the axis of the air circuit 4170. The heating element may be in communication with a controller such as a central controller 4230. One example of an air circuit 4170 comprising a heated wire circuit is described in United States Patent 8,733,349, which is incorporated herewithin in its entirety by reference.

[0101] In one form of the present technology, supplementary gas, e.g. oxygen, 4180 is delivered to one or more points in the pneumatic path, such as upstream of the pneumatic block 4020, to the air circuit 4170, and/or to the patient interface 3000 or 3800.

5.6 HUMIDIFIER

[0102] In one form of the present technology there is provided a humidifier 5000 (e.g. as shown in Fig. 5A) to change the absolute humidity of air or gas for delivery to a patient relative to ambient air. Typically, the humidifier 5000 is used to increase the absolute humidity and increase the temperature of the flow of air (relative to ambient air) before delivery to the patient’s airways.

[0103] The humidifier 5000 may comprise a humidifier reservoir 5110, a humidifier inlet 5002 to receive a flow of air, and a humidifier outlet 5004 to deliver a humidified flow of air. In some forms, as shown in Fig. 5A and Fig. 5B, an inlet and an outlet of the humidifier reservoir 5110 may be the humidifier inlet 5002 and the humidifier outlet 5004 respectively. The humidifier 5000 may further comprise a humidifier base 5006, which may be adapted to receive the humidifier reservoir 5110 and comprise a heating element 5240.

[0104] According to one arrangement, the humidifier 5000 may comprise a water tank or reservoir 5110 configured to hold, or retain, a volume of liquid (e.g. water) to be evaporated for humidification of the flow of air. The water reservoir 5110 may be configured to hold a predetermined maximum volume of water in order to provide adequate humidification for at least the duration of a respiratory therapy session, such as one sleep session. Typically, the reservoir 5110 is configured to hold several hundred millilitres of water, e.g. 300 millilitres (ml), 325 ml, 350 ml or 400 ml. In other forms, the humidifier 5000 may be configured to receive a supply of water from an external water source such as a water supply system of a building. The RPT device 4000 may control a valve to automatically add water to the reservoir 5110 when the level of water is low.

[0105] According to one aspect, the water reservoir 5110 is configured to add humidity to a flow of air from the RPT device 4000 as the flow of air travels therethrough. In one form, the water reservoir 5110 may be configured to encourage the flow of air to travel in a tortuous path through the reservoir 5110 while in contact with the volume of water therein.

[0106] According to one form, the reservoir 5110 may be removable from the humidifier 5000, for example in a lateral direction as shown in Fig. 5A and Fig. 5B. The reservoir 5110 may be removed for being filled with water prior to operating the RPT device 4000. Alternatively, a source of water may be fluidly connected to the reservoir 5110 to add water to the reservoir when needed.

[0107] The reservoir 5110 may also be configured to discourage egress of liquid therefrom, such as when the reservoir 5110 is displaced and/or rotated from its normal, working orientation, such as through any apertures and/or in between its sub-components. As the flow of air to be humidified by the humidifier 5000 is typically pressurised, the reservoir 5110 may also be configured to prevent losses in pneumatic pressure through leak and/or flow impedance. [0108] According to one arrangement, the reservoir 5110 comprises a conductive portion 5120 configured to allow efficient transfer of heat from the heating element 5240 to the volume of liquid in the reservoir 5110. In one form, the conductive portion 5120 may be arranged as a plate, although other shapes may also be suitable. All or a part of the conductive portion 5120 may be made of a thermally conductive material such as aluminium (e.g. approximately 2 mm thick, such as 1 mm, 1.5 mm, 2.5 mm or 3 mm), another heat conducting metal or some plastics. In some cases, suitable heat conductivity may be achieved with less conductive materials of suitable geometry.

[0109] In one form, the humidifier 5000 may comprise a humidifier reservoir dock 5130 (as shown in Fig. 5B) configured to receive the humidifier reservoir 5110. In some arrangements, the humidifier reservoir dock 5130 may comprise a locking feature such as a locking lever 5135 configured to retain the reservoir 5110 in the humidifier reservoir dock 5130.

[0110] The humidifier reservoir 5110 may comprise a water level indicator 5150 as shown in Fig. 5A-5B. In some forms, the water level indicator 5150 may provide one or more indications to a user such as the patient 1000 or a care giver regarding a quantity of the volume of water in the humidifier reservoir 5110. The one or more indications provided by the water level indicator 5150 may include an indication of a maximum, predetermined volume of water, any portions thereof, such as 25%, 50%, or 75% or volumes such as 200 ml, 300 ml, or 400ml. [0111] The humidifier 5000 may comprise one or more humidifier transducers (sensors) 5210 instead of, or in addition to, transducers 4270 described above. Humidifier transducers 5210 may include one or more of an air pressure sensor 5212, an air flow rate transducer 5214, a temperature sensor 5216, or a humidity sensor 5218. A humidifier transducer 5210 may produce one or more output signals which may be communicated to a controller such as the central controller 4230 and/or the humidifier controller 5250. In some forms, a humidifier transducer may be located externally to the humidifier 5000 (such as in the air circuit 4170) while communicating the output signal to the controller 5250.

5.7 TRAN SDU CER(S)

[0112] An RPT system may comprise one or more transducers (sensors) 4270 configured to measure one or more of any number of parameters in relation to an RPT system, its patient, and/or its environment. A transducer may be configured to produce an output signal representative of the one or more parameters that the transducer is configured to measure. [0113] The output signal may be one or more of an electrical signal, a magnetic signal, a mechanical signal, a visual signal, an optical signal, a sound signal, or any number of others which are known in the art. [0114] A transducer may be integrated with another component of an RPT system, where one exemplary arrangement would be the transducer being internal of an RPT device. A transducer may be substantially a ‘standalone’ component of an RPT system, an exemplary arrangement of which would be the transducer being external to the RPT device.

[0115] A transducer may be configured to communicate its output signal to one or more components of an RPT system, such as an RPT device, a local external device, or a remote external device. External transducers may be for example located on a patient interface, or in an external computing device, such as a smartphone. External transducers may be located for example on or form part of the air circuit, e.g., the patient interface.

[0116] The one or more transducers 4270 may be constructed and arranged to generate signals representing properties of air such as a flow rate, a pressure or a temperature. The air may be a flow of air from the RPT device to a patient, a flow of air from the patient to the atmosphere, ambient air or any others. The signals may be representative of properties of the flow of air at a particular point, such as the flow of air in the pneumatic path between the RPT device and the patient. In one form of the present technology, one or more transducers 4270 are located in a pneumatic path of the RPT device, such as downstream of the humidifier 5000.

[0117] In accordance with one aspect of the present technology, the one or more transducers 4270 comprises a pressure sensor located in fluid communication with the pneumatic path. An example of a suitable pressure sensor is a transducer from the HONEYWELL ASDX series. An alternative suitable pressure sensor is a transducer from the NPA Series from GENERAL ELECTRIC. In one implementation, the pressure sensor is located in the air circuit 4170 adjacent the outlet 5004 of the humidifier 5000.

[0118] The acoustic sensor (microphone) 4278 may be configured to generate a sound signal representing the variation of pressure within the air circuit 4170. In this example, the microphone 4278 may be configured to detect acoustic signals from a sound source through the reservoir 5110 to determine the water level. The sound signal from the microphone 4278 may be received by the central controller 4230 for acoustic processing and analysis as configured by one or more of the algorithms 4300 described below. The microphone 4278 may be directly exposed to the airpath for greater sensitivity to sound, or may be encapsulated behind a thin layer of flexible membrane material. This membrane may function to protect the microphone 4278 from heat and/or humidity. 5.8 ACOUSTIC ANALYSIS

[0119] According to one or more aspects of the present technology, acoustic analysis may be used to determine operating parameters of the RPT based system shown in FIG. 4B. As will be clear in the context of the remainder of the document, the terms ‘acoustic’, ‘sound’, or ‘noise’ in the present document are generally intended to include airborne vibrations, regardless of whether they may be audible or inaudible. As such, the terms ‘acoustic’, ‘sound’, or ‘noise’ in the present document are intended to include airborne vibrations in the ultrasonic, or subsonic ranges, unless specifically stated otherwise.

[0120] Some implementations of the disclosed acoustic analysis technologies may implement deconvolution analysis such as cepstrum analysis or auto-cepstrum analysis. Other acoustic analysis techniques such as spectral analysis or auto-correlation may be used. Cepstrum analysis may include real or complex power cepstrum, and may alternatively be autocepstrum. [0121] A cepstrum may be considered the inverse Fourier Transform of the log spectrum of the forward Fourier Transform of the decibel spectrum, etc. The operation essentially can convert a convolution of an impulse response function (IRF) and a sound source into an addition operation so that the sound source may then be more easily accounted for or removed so as to isolate data of the IRF for analysis. Techniques of cepstrum analysis are described in detail in a scientific paper entitled “The Cepstrum: A Guide to Processing: (Childers et al, Proceedings of the IEEE, Vol. 65, No. 10, Oct 1977) and Randall RB, Frequency Analysis, Copenhagen: Bruel & Kjaer, p. 344 (1977, revised ed. 1987). The application of cepstrum analysis to respiratory therapy system component identification is described in detail in PCT Publication No. W02010/091462, titled “Acoustic Detection for Respiratory Treatment Apparatus”, the entire contents of which are hereby incorporated by reference.

[0122] Cepstrum analysis may be understood in terms of the property of convolution. The convolution of / and g can be written as /* g. This operation may be the integral of the product of the two functions (/ and g) after one is reversed and shifted. As such, it is a type of integral transform as follows:

[0123] While the symbol t is used above, it need not represent the time domain. But in that context, the convolution formula can be described as a weighted average of the functional) at the moment t where the weighting is given by simply shifted by amount t. As t changes, the weighting function emphasizes different parts of the input function. [0124] A mathematical model that can relate output to the input for a time-invariant linear acoustic system, such as the pneumatic path of a respiratory therapy system, can be based on convolution. For example, a sound generator such as the motor 4144 of the blower 4120 may generate sound that is sensed by the microphone 4278 in FIG. 4B. The sound signal generated by the microphone 4278 in the air circuit 4170 in response to the sound may be considered as an input sound signal “convolved” with the system Impulse Response Function (IRF) as a function of time (t). where y{t) is the output sound signal generated by the microphone 4278; .s i (!) is the input sound signal such as sound generated in or by the motor 4144 of a respiratory therapy device 4000, and hl(t) is the system IRF from the sound source to the microphone 4278. The system IRF hl(t) may be thought of as the system response to a unit impulse input.

[0125] Conversion of Equation (2) into the frequency domain by means of the Fourier Transform of the sound signal y{t) (e.g., a discrete Fourier Transform (“DFT”) or a fast Fourier transform (“FFT”)) and considering the Convolution Theorem, the following equation is produced: where Y(f) is the Fourier Transform (spectrum) of y(t); Sl(f) is the Fourier Transform of .s i (t); and H\(f) is the Fourier Transform of h\ (t) In other words, a convolution in the time domain becomes a multiplication in the frequency domain.

[0126] A logarithm operation may be applied to Equation (3) so that the multiplication is converted into an addition:

[0127] Equation (4) may then be converted back into the time domain, by an Inverse Fourier Transform (IFT) (e.g., an inverse DFT or inverse FFT), which results in a complex-valued “Cepstrum” - the inverse Fourier Transform of the logarithm of the spectrum Y(f) :

The abscissa is a real-valued variable known as quefrency, with units measured in seconds. Effects that are convolutive in the time domain thus become additive in the logarithm of the spectrum, and remain so in the cepstrum or quefrency domain. In particular, the output cepstrum consists of two additive components: the cepstrum of the input signal si(f), and the cepstrum of the system

[0128] Consideration of the data from a cepstrum analysis, such as examining the data values in the quefrency domain, may provide information about the RT system. For example, by comparing cepstrum data of a system from a prior or known baseline of cepstrum data for the system, the comparison, such as a difference, can be used to recognize differences or similarities in the system that may then be used to implement automated control for varying functions or purposes.

[0129] In this example, acoustic analysis may be used to automatically determine the water level in the reservoir 5110 of the humidifier 5000 in FIGs. 5A-5B. The water level in the reservoir 5110 may be measured acoustically in numerous ways using different sound sources/signals using a range of signal processing techniques as will be explained.

[0130] Sound propagates at differing speeds through different mediums and an acoustic reflection will occur at any interface where there is a change in acoustic impedance (such as between water and air). This fact is leveraged to enable estimation of either relative or absolute changes in the water level within the reservoir 5110 of the humidifier 5000 in FIGs. 5A-5B. [0131] FIG. 6 is a block diagram of an acoustic water level determination system 6000 that may be applied to the RPT 4000 and the humidifier 5000 in FIG. 4B. The water level determination system 6000 includes a sound generator 6010, a filter 6012 that models the water level in the reservoir 5110, and an acoustic sensor 6014. In this example the acoustic sensor 6014 may be the microphone 4278 in FIG. 4C. The acoustic sensor 6014 is coupled to an analysis engine 6020. The analysis engine 6020 may be part of the algorithm 4300 executed by the controller 4230.

[0132] In this example, the acoustic sensor 6014 is at one end of an air conduit 6030. The other end of the conduit 6040 is connected to a mask 6032 worn by the patient. Sound input signals (e.g. an impulse) enters the acoustic sensor 6014. The acoustic sensor 6014 may therefore pick up multiple sounds. As explained above, certain sounds may be used for determination of water level in the reservoir 5110. Other sounds such as breathing sounds of the patient 1000 may be used for other purposes such as health analysis or component identification. The sounds also travel along the airpath in the conduit 6030 to a mask 6032 and is reflected back along the conduit 6020 by features in the airpath (which includes the conduit and the mask) to enter the acoustic sensor 6014 once more. Other sounds may be reflected by other components such as the reservoir 5110. [0133] In one example method, the sound generator 6010 may be the motor 4144 in FIG. 4B. The sound from other components of the RPT 4000 such as sound generated by the motor windings of the motor 4144, the pump or the power supply may be used as the sound generator 6010. Thus, the sound generated by the flow generator blower such as by the motor 4144 in FIG. 4B may be analyzed after passing through or being reflected by the humidification reservoir 5110 to determine the water level in the reservoir 5110. The reservoir 5110 acts as the acoustic filter 6012 on the sound signal. The acoustic properties of the equivalent filter 6012 change as the water level in the reservoir 5110 changes.

[0134] In this example, the audio signal of the operation of the motor 4144 filtered by the water in the reservoir 5110 may be sensed by the microphone 4278 within the air circuit 4170. Alternatively, other acoustic sensors such as the external audio sensor 4279 may be used as the acoustic sensor 6014 to detect the audio signal for these purposes. In this example, the reservoir 5110 may be interposed between the sound generation source 6010 and the acoustic sensor 6014.

[0135] The water level may be estimated by the analysis engine 6020 using spectral analysis or cepstral analysis of a detected acoustic signal in conjunction with other measurements such as pressure or temperature that may influence sounds from the sound generator 6010. For example, the air temperature will influence the speed of the propagated sound waves affecting the time of flight of the sound to and from the reservoir 5110. Hence, a temperature measurement may be taken into account to calibrate the correct region of interest for analysis. Similarly, the speed of the flow generator motor 4144 will influence the frequency content of the generated sound and thus by including motor speed either as an input to a prediction model or by compensating for this during signal preprocessing such as supressing undesirable frequencies associated with the motor speed and its harmonics. As explained above, cepstrum analysis may be used to classify the analyzed sound in relation to a baseline. The cepstrum analysis may also be used to filter out other sounds such as breathing sounds from the patient and other noise sources.

[0136] Another example of acoustic signals for determining water level includes using an audio speaker as the sound generator 6010 in proximity to the reservoir 5110. Thus the sound generator may be positioned on or within the reservoir 5110. Sound from an audio speaker is detected by the acoustic sensor 6014 after being filtered by the water in the reservoir 5110 if the reservoir 5110 is arranged between the acoustic sensor 6014 and the speaker. Alternatively, a reflected or otherwise affected/altered sound from the reservoir 5110 originating from the audio sensor may be used for the analysis. For example, if the sound generator is located near the acoustic sensor 6014, the water level may be estimated based on analysis of the detected reflected sound from the acoustic sensor determined in contrast with the original sound signal. [0137] An audio speaker may generate a sound impulse or white noise. This may be particularly useful for respiratory therapy systems with very quiet blowers that do not generate much noise. For example, when using a ResMed™ RPT device at speeds generally less than 6 krpm, the blower is very quiet. Under this condition, using the sound of the blower as a sound source to produce the input signal might be insufficient for determining the water level in the reservoir 5110. This may be overcome by including an additional sound source in the airpath. This may be activated during time periods of measurement such as when the mask is initially attached to the conduit. While an additional sound source might be a speaker, other sound emitters might be utilized. For example, a simple acoustic generator might be configured to vibrate in response to the flow of air from the RPT device such as a reed that may be selectively activated and deactivated (e.g., mechanically applied and removed from the airpath of the system). This may then serve to selectively create the sound impulse. Alternatively, an actuated valve of the RPT device may serve as the additional sound source.

[0138] Additionally, a sound source such as a speaker may be used to fill in gaps in the sound spectrum created by the mechanical components of the RPT device 4000. For example, a speaker may be used to produce a signal designed to have a particular spectrum such that the addition of the blower noise and the speaker sound produce a white spectrum. This may improve detection accuracy of the system as well as improve the perceived quality of the sound that the therapy device user experiences.

[0139] Using a speaker as the sound generator 6010 allows the use of a pre-determined sound having a specially designed waveform such as frequency modulated continuous wave (FMCW), frequency hopping range gating (FHRG), continuous wave (CW), pulsed continuous wave, narrow band, ultra wide band (UWB), or other wave forms such as a white noise sensing signal. The waveform may additionally or alternatively include a coded sound such as amplitude-shift keying (ASK), frequency-shift keying (FSK), or phase-shift keying (PSK), etc. The speaker may also be or comprise a transducer such as a buzzer. These sounds may be audible or preferably inaudible to the human ear. These signals may be demodulated to infer the time of flight of the acoustic wave from the sound generator 6010 to the acoustic sensor 6014, which will change as the water level decreases in the reservoir 5110.

[0140] The use of a speaker for the sound generator 6010 allows measurement of the water level in the reservoir 5110 without the motor 4144 operating. Further, a speaker may allow emission of a pure white noise in contrast to the motor 4144 that does not generate pure white noise. Pure white noise allows simpler signal processing because of the constant power spectrum density.

[0141] FIG. 7 A is a graph 700 of the noise spectrum of acoustic signals received by the acoustic sensor 4278 that are filtered by the water volume in the reservoir 5110 over a pre-determined sample time such as one minute. The graph 700 plots the Fourier transform of the detected signals that are associated with the magnitude of the relative energy of detected noise spectrum against frequency. The converted sound signal received when the water level in the reservoir 5110 is full is represented by a trace 710. The trace 712 represents the converted signal received when the reservoir 5110 is empty. Different levels of water in the reservoir 5110 produce converted signals represented by traces 714, 716, 718 between the traces 710 and 712. Thus, the trace 714 represents a 25% water level, the trace 716 represents a 50% water level, and the trace 718 represents a 75% water level. The amplitudes at certain frequencies for a detected signal spectrum may be used to determine the level of water in the reservoir 5110. A library of baseline amplitudes may be stored for different levels, and a comparison of the determined amplitudes may be used to approximate the water level. Different sets of baseline amplitude values may be stored for each different sized reservoir, and the corresponding set of baseline values may be used for the comparison depending on the size of the reservoir 5110. [0142] FIG. 7B shows a graph 750 of the results of the cepstrum analysis performed on the acoustic signals received with the reservoir 5110 is full or empty. Cepstrum analysis is performed on the received signals of traces 710, 712, 714, 716 and 718 in FIG. 7A. The graph 750 plots the cepstrum amplitude against distance between the acoustic sensor 6014 and the reservoir 5110. A cesptrum signal may be considered in the quefrency domain, however, the abscissa may be approximately represented as distance by considering the velocity of sound in the propagating medium in conjunction with the time of flight of the reflected waves. This allows the analysis of reflections that occur at specific distances from the acoustic sensor 6014. Thus, a trace 760 represents the cepstrum amplitude when the water level in the reservoir 5110 is full, and a trace 762 represents the cepstrum amplitude when the reservoir 5110 is empty. The other traces 764, 766, and 768 represent the cepstrum amplitudes relating to other levels of water in the reservoir 5110.

[0143] In the graph 750, the distance of the reservoir 5110 from the acoustic sensor 6014 is plotted on the x-axis. As shown in FIG. 7B, the cepstrum amplitude will change at the distance of the tub due to the water level changing (lowering). As water is emptied from the reservoir 5110, a gradual change in the amplitudes of the trace 760 will occur as the time of flight of the reflected sound increases, shifting the energy of the signal around the approximate distance to the reservoir 5110 to the right of the graph 750 over time. The trace represents the relative energy and phase of a multitude of reflections through the reservoir 5110. The routine translates the abscissa of the trace from quefrency into distance using the speed of sound and the measured flight time of the reflections. Thus, the trace 762 representing the empty reservoir 5110, is measurably different than the trace 760 representing the full reservoir 5110 in a consistent fashion that includes a gradual shift from full to empty. A library of baseline cepstrum amplitude signatures may be stored for different levels, and a comparison of the determined cepstrum amplitudes may be used to approximate the water level. Different sets of baseline cepstrum amplitude signature values may be stored for each different sized reservoir, and the corresponding set of baseline values may be used for the comparison depending on the size of the reservoir 5110.

[0144] Similar to a muffler, as the volume of water in the reservoir 5110 is increased, the sound is dampened further. Thus, as the water level decreases, the volume of the reservoir 5110 containing air increases and will cause the sound amplitude to be altered. The reservoir 5110 acts as the filter 6012 in FIG. 6 on the sound blown through it and as the reservoir 5110 empties, the filter characteristics change with the water level.

[0145] If the motor 4144 is used as the sound generator 6110, changing speeds of the motor 4144 will result in a change in the sound from the operation of the motor 4144. Such changes require compensation of the sensed acoustic signal. The speed can change the acoustic output, but the motor speeds appear in the spectrum so the analysis engine 6020 in FIG. 6 may compensate for the change in speed. A series of peaks associated with the motor speed and the associated harmonics or overtones may appear in the cepstrum signals.

[0146] The speed of the motor (rpm) may be input from the motor speed sensor 4276 in FIG. 4C. Alternatively, the air pressure supplied by the RPT 4000 may be measured from the pressure sensor 4272 or the flow rate sensor 4272 to determine the rpm. The rpm may be an input to the analysis so it is normalized and the different speeds of the motor 4144 do not negatively impact the determination. This may involve inputting this parameter directly into a machine learning prediction model which will “learn” to account for changes due to rpm or, for example, by suppressing these artifacts using filtering in a pre-processing stage of the analysis.

[0147] Another source of interference may be breathing sounds from the patient that are transmitted through the air flow circuit 4170. The sampling of the sound from the sound generator 6010 could be limited to pauses between inspiration and expiration. The flow signal from the flow generator 4140 could be used as a trigger for when the controller 4230 samples the output of the acoustic sensor 6014. In order to minimize the varying effect of the breathing cycle on the acoustic characteristics of the airpath, and hence the variability of the acoustic signature between windows, the windows may be timed to coincide (synchronised) with a particular point in the breathing cycle, such as the peak of inspiratory flow rate or the pause at the end of expiration. In a similar manner, the window may be synchronised with a particular shaft rotation speed of motor 4144 in order to either reduce or highlight the influence of rotating machinery on the signature. In some embodiments, the acoustic analysis may include diagnosis or prognosis of machine conditions, such as bearing faults.

[0148] The controller 4230 may also include an algorithm to filter out breathing noises so the noise associated with breathing is not negatively impacting the analysis. In some embodiments, the acoustic signals are sensed at the beginning of inhalation (or end of exhalation) and/or end of inhalation (or beginning of exhalation) in a breathing cycle since there is essentially no flow of air due to breathing, in order to avoid the noises associated with breathing.

[0149] Although it is preferred that the acoustic sensor 6014 is downstream from the reservoir 5110, the acoustic sensor 6014 may be located in the reservoir 5110 or other locations. In some examples, the cepstrum analysis may be performed on reflected sound through the reservoir 5110 compared with the sound source. The separation of the reflected signal in relation to the detected original acoustic signal is performed and the reflected sound is analyzed to determine the water level in the reservoir.

[0150] In an example where the sound generator is not located downstream of the reservoir 5110, the water level can be determined by a reflection of a sound through the reservoir 5110. For example, if the sound of the patient breathing is received by the acoustic sensor 6014 for other purposes such as mask identification, the sound and its reflection may be used for water level determination in the reservoir. In this example, the system impulse response function (IRF) (the output signal produced by an input impulse) therefore acoustic sensor 6014 contains an input signal component and a reflection component. A key feature in this example is the time taken by sound to travel from one end of the reservoir 5110 to the opposite end. This interval is manifested in the system impulse response function (IRF) because the acoustic sensor 6014 receives the input signal coming from the sound generator 6012, and then some time later receives the input signal reflected and filtered by the reservoir 5110. This means that the component of the system IRF associated with the reflection from reservoir 5110 (the reflection component) is delayed in relation to the component of the system IRF associated with the input signal (the input signal component), which arrives at the microphone after a relatively brief delay. For practical purposes, this brief delay may be ignored and zero time approximated to be when the microphone first responds to the input signal. The delay is equal to 2 Lie (wherein L is the length of the conduit, and c is the speed of sound in the reservoir 5110).

[0151] Another feature of the acoustic system in FIG. 6 is that because the airpath is loss- prone, provided the path through the reservoir 5110 is long enough, the input signal component decays to a negligible amount by the time the reflection component of the system IRF has begun. If this is the case, then the input signal component may be separated from the reflection component of the system IRF.

[0152] The cepstrum of the system IRF associated with equations (2), (4), and (5) previously described has generally the same the properties as the system That is, the cepstrum comprises a reflection component concentrated around a quefrency of 2 L/c as well as an input signal component concentrated around quefrency zero. In the present technology, the cepstrum analysis may be configured to separate the reflection component of the output cepstrum from other system artifacts (including but not limited to the input signal component e.g., by examination of the position and amplitude of the output cepstrum data.

[0153] This separation may be accomplished if the input signal is either transient (e.g. an impulse), or stationary random, which means the input signal component of the cepstrum will be concentrated around a quefrency of zero. For example, the input signal may be the sound produced by an RPT device running at a constant speed during the time period of the microphone’s measurement. This sound may be described as “cyclostationary.” That is, it is stationary random, and periodic in its statistics. This means that the input signal and the reflection component of the system IRF may be “smeared” across all measured times of the output signal y{t) because at any point in time, the output signal y (t) is a function of all previous values of the input signal and system IRF (see equation (2)). However, the cepstrum analysis described above may be implemented to separate the reflection component of the output cepstrum U(t) from this convolutive mixture.

[0154] For example, the reflection component of a particular water level in a reservoir being tested (the “signature”) may be separated from the cepstrum of the output signal generated by the acoustic sensor. This signature may be compared to that of previous or predetermined signatures of known water levels stored as a data template. One way of doing this is to calculate the cross-correlation between the signature of the reservoir and previously stored signatures for all known water levels. There is a high probability that the cross-correlation with the highest peak corresponds to the water level of the reservoir, and the location of the peak should be proportional to the distance to the reservoir.

[0155] However, more points of correlation may also increase the accuracy of the analysis of the present technology as to the precise water level. Thus, additional data points may be utilized. Optionally, a least squares algorithm with the test data and known data sets may be implemented in the identification of water level. Still further, in some embodiments additional feature extraction and recognition techniques may be utilized, which may be based on artificial intelligence / machine learning structures and strategies such as a neural network or a support vector machine. Other sources of information may also be included as inputs to such structures and strategies to improve the accuracy of identification of the water level. Examples are the alteration of the noise, temperature, humidity, motor speed, pressure, flow rate, patient interface type, conduit type/size, reservoir type/size, time since the therapy session began and humidification settings.

[0156] Even in such “breathing-synchronised” implementations, other sources of airpath variability between windows may affect the relative delay of each acoustic signature in the quefrency domain. Depending on how the acoustic signatures are combined, this may cause the combined acoustic signature to be smeared or blurred, affecting its distinctiveness.

[0157] In some implementations, therefore, a method of combination may be chosen that is robust to small variations in delay (relative shifts along the quefrency axis) between the multiple acoustic signatures. In one such implementation, the newly computed acoustic signatures are combined one by one into a cumulative acoustic signature. Each newly computed signature may be correlated with the cumulative acoustic signature to estimate its delay relative to the cumulative acoustic signature, and that estimated relative delay may be compensated for when including the newly computed signature in the cumulative acoustic signature.

[0158] Other techniques may produce a combined signature that is robust to small variations in delay, e.g. a wavelet transform-based combination.

[0159] Fig. 8 is a flow chart illustrating a method 800 of identifying the water level of the reservoir 5110 of a respiratory therapy system in accordance with one aspect of the present technology. The method 800 samples the acoustic output of the acoustic sensor 6014 (810). The sampling preferably occurs during a period of time where there are minimal other sounds to interfere with the signal. The method 800 then computes the output cepstrum from the output signal y(t ) during a breathing-synchronised window as described above in relation to equation (5) (812). The cepstrum analysis optionally flattens the log spectrum Log{Y(f)} before computing the output cepstrum U(t) as described above.

[0160] The acoustic signature from the cepstrum analysis is combined with a cumulative acoustic signature in a manner robust to small shifts in the quefrency domain, as described above (814). In a first pass through the loop, the method 800 simply designates the acoustic signature as the cumulative acoustic signature. The method 800 checks whether sufficient acoustic signatures have been combined to make up the cumulative acoustic signature (816). [0161] If not (“N”), the method 800 proceeds to step 818, which awaits the next breathing- synchronised window before returning to step 810 to compute a new cepstrum. If so (“Y”), the method 800 compares the cumulative signature with a predefined or predetermined library of previously measured acoustic signatures obtained from expected acoustic signature of different water levels (820). The method 800 then matches the acoustic signature and outputs the nearest water level (822). The method 800 then determines whether the water level is low (824). If the water level is not low, the method 800 loops back to continue sampling data from the next synchronized window (818). If the water level is low, the method 800 issues an alert (826).

[0162] In some embodiments, greater blower speeds than the speeds illustrated above may be implemented during water level determination. For example, some conduits use materials with properties that may reduce noise. In such a system, the acoustic losses of the system may fluctuate. If the losses increase as detected by the measured signal (e.g., amplitude decrease), the decibels of the sound or noise source may be increased to overcome the effects of sound loss. This may be achieved by increasing the speed of the blower during a test measurement. Additionally, other elements included in the airpath may increase the acoustic losses. These elements may include noise baffles and valves. The loss attributable to these components may also be overcome by increasing the noise source level or amplitude. Typically, a suitable sound level for the input signal may be about 20 dBa or greater.

[0163] The frequency range of the microphone 4270 may be selected according to the geometric resolution required for the component identification. Resolving information about small dimensions will typically require high frequency content in the generated sound signal. A typical air circuit for respiratory therapy might exhibit tube resonances with a fundamental frequency of less than 100 Hz, but with higher harmonics appearing in the spectrum as integer multiples of the fundamental frequency up to more than 10 kHz. The frequency range of the microphone 4270 may be selected to be large enough to allow sensing of enough of the resonant harmonics that the periods associated with the harmonic spacing are present in the inverse Fourier Transform of the log spectrum. In one implementation, therefore, the microphone 4270 has an upper frequency limit of at least 10 kHz.

[0164] In some embodiments, autocorrelation (i.e., the inverse Fourier Transform of the power spectrum) may be implemented rather than cepstrum analysis.

[0165] The operation of the example RPT device 4000 may be improved by the example sensor system. In this example, the controller 4230 may perform an acoustic signal analysis to determine the water level in the reservoir 5110 on start up of the RPT device 4000. By determining the water level in the humidifier reservoir 5110, numerous actions could be taken to help improve the patient experience automatically. For example, the controller 4230 may adjust the settings of the water heater element 4250 in real-time to compensate for a low water level. If the water level is low, the temperature of the heating element 4250 may be decreased with the aim to maintain some humidity/water in the reservoir 5110 until the end of a given sleep session. Using the water level data, the user may be informed that the water level is running low between sleep sessions and then the user may be alerted to add the needed water. The controller 4230 may be programmed to provide feedback to the user on their humidification settings and prompt a change in humidification settings to preserve water in the reservoir 5110 during sleep session. Alternatively, the controller 4230 may communicate with an external device that may provide a recommendation to a user to get a larger reservoir. [0166] Thus, the controller 4230 may provide a warning when the acoustic signal drops below a pre-determined threshold indicating the reservoir 5110 is low on water. The controller 4230 may display a warning on a display such as the display 4294 in FIG. 4C or other displays such as an external LED. Other warning indicators such as an audio alarm may be triggered by the controller 4230 in addition, or separately, from the visual indicator. As explained above, the controller 4230 may also be configured to control a valve to a water supply to add water to the reservoir 5110 if low water is determined.

[0167] The system also allows the provision of a warning to a user that the reservoir 5110 is overfilled using this method. The monitoring of a condition where the reservoir 5110 is overfilled addresses potential issues such as the higher likelihood of water being pushed into the air circuit 4170 and cause gurgling. This also solves the problem of the reservoir 5110 being too full causing the air coming into the reservoir 5110 to impact the therapy/pressure from the RPT device 4000. An alert of an overfill allows a user to empty the excess water from the reservoir 5110.

[0168] The controller 4230 may also include a routine that identifies water leaking from the reservoir 5110 if measurements over time of the level of the water change more rapidly than typical use of the humidifier 5000. The controller 4230 may provide an alert to replace the faulty reservoir 5110.

[0169] The data related to the fill levels of the reservoir over sessions of the using the RPT device 4000 may be used to assist in optimizing respiratory therapy for the user. The water level in the humidifier reservoir 5110 may be descriptive of or may be used to infer issues with the respiratory device such as RPT device 4000, comprising a humidifier reservoir, such as humidifier 5000, the user interface, such as user interface 300, and/or the conduit, such as air conduit 4170. For example, a decrease in the water level of the humidifier reservoir 5110 across one or more therapy sessions may deviate from an expected decrease or pattern of decrease in water levels compared to previously monitored decreases in the water level. The baseline of a predetermined/expected decrease in water level may be determined in view of a humidity setting on the RPT device 4000, on a learned typical decrease in water level for a particular user (based on data specific to the user or a population with similar demographic traits to the user), a particular therapy, a particular user interface, and/or ambient conditions in a room (e.g., humidity, temperature, etc).

[0170] If the decrease in the level of water is less than what is expected, this may be indicative of an issue with the humidifier 5000, e.g., a fault with the heating plate or blockage from the reservoir 5110. As explained above, the user and/or manufacturer may be notified to provide repair or replacement.

[0171] If the decrease in the level of water in the reservoir 5110 is greater than what is expected, this could be indicative of (greater than expected/tolerated) unintentional leak, e.g., mask leak or mouth leak. As such, as well as an alert to notify the user of low water levels, an alert to indicate that there may be an issue with the respiratory system or setup, optionally requiring further investigation / troubleshooting, could be sent to the user (optionally via a display on the RPT 4000) or a third party such as a healthcare provider or a vendor.

5.9 GLOSSARY

[0172] For the purposes of the present technology disclosure, in certain forms of the present technology, one or more of the following definitions may apply. In other forms of the present technology, alternative definitions may apply.

General

[0173] Air: In certain forms of the present technology, air may be taken to mean atmospheric air, and in other forms of the present technology air may be taken to mean some other combination of breathable gases, e.g. atmospheric air enriched with oxygen. [0174] Ambient: In certain forms of the present technology, the term ambient will be taken to mean (i) external of the respiratory therapy system or patient, and (ii) immediately surrounding the respiratory therapy system or patient.

[0175] For example, ambient humidity with respect to a humidifier may be the humidity of air immediately surrounding the humidifier, e.g. the humidity in the room where a patient is sleeping. Such ambient humidity may be different to the humidity outside the room where a patient is sleeping.

[0176] Automatic Positive Airway Pressure (APAP) therapy: CPAP therapy in which the treatment pressure is automatically adjustable, e.g. from breath to breath, between minimum and maximum limits, depending on the presence or absence of indications of SDB events. [0177] Continuous Positive Airway Pressure (CPAP) therapy: Respiratory pressure therapy in which the treatment pressure is approximately constant through a respiratory cycle of a patient. In some forms, the pressure at the entrance to the airways will be slightly higher during exhalation, and slightly lower during inhalation. In some forms, the pressure will vary between different respiratory cycles of the patient, for example, being increased in response to detection of indications of partial upper airway obstruction, and decreased in the absence of indications of partial upper airway obstruction.

[0178] Flow rate: The volume (or mass) of air delivered per unit time. Flow rate may refer to an instantaneous quantity. In some cases, a reference to flow rate will be a reference to a scalar quantity, namely a quantity having magnitude only. In other cases, a reference to flow rate will be a reference to a vector quantity, namely a quantity having both magnitude and direction. Flow rate may be given the symbol Q. ‘Flow rate’ is sometimes shortened to simply ‘flow’ or ‘airflow’.

[0179] Leak: The word leak will be taken to be an unintended flow of air. In one example, leak may occur as the result of an incomplete seal between a mask and a patient's face. In another example leak may occur in a swivel elbow to the ambient.

[0180] Patient: A person, whether or not they are suffering from a respiratory condition. [0181] Pressure: Force per unit area. Pressure may be expressed in a range of units, including cmH20, g-f/cm2 and hectopascal. 1 cmH20 is equal to 1 g-f/cm2 and is approximately 0.98 hectopascal. In this specification, unless otherwise stated, pressure is given in units of cmH20. [0182] Respiratory Pressure Therapy (RPT): The application of a supply of air to an entrance to the airways at a treatment pressure that is typically positive with respect to atmosphere. [0183] Seal: May be a noun form ("a seal") which refers to a structure, or a verb form (“to seal”) which refers to the effect. Two elements may be constructed and/or arranged to ‘seal’ or to effect ‘sealing’ therebetween without requiring a separate ‘seal’ element per se.

Patient interface

[0184] Plenum chamber: a mask plenum chamber will be taken to mean a portion of a patient interface having walls at least partially enclosing a volume of space, the volume having air therein pressurised above atmospheric pressure in use. A shell may form part of the walls of a mask plenum chamber.

[0185] Shell: A shell will be taken to mean a curved, relatively thin structure having bending, tensile and compressive stiffness. For example, a curved structural wall of a mask may be a shell. In some forms, a shell may be faceted. In some forms a shell may be airtight. In some forms a shell may not be airtight.

[0186] Vent: (noun): A structure that allows a flow of air from an interior of the mask, or conduit, to ambient air for clinically effective washout of exhaled gases. For example, a clinically effective washout may involve a flow rate of about 10 litres per minute to about 100 litres per minute, depending on the mask design and treatment pressure.

5.10 OTHER REMARKS

[0187] A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in Patent Office patent files or records, but otherwise reserves all copyright rights whatsoever.

[0188] Unless the context clearly dictates otherwise and where a range of values is provided, it is understood that each intervening value, to the tenth of the unit of the lower limit, between the upper and lower limit of that range, and any other stated or intervening value in that stated range is encompassed within the technology. The upper and lower limits of these intervening ranges, which may be independently included in the intervening ranges, are also encompassed within the technology, subject to any specifically excluded limit in the stated range. Where the stated range includes one or both of the limits, ranges excluding either or both of those included limits are also included in the technology.

[0189] Furthermore, where a value or values are stated herein as being implemented as part of the technology, it is understood that such values may be approximated, unless otherwise stated, and such values may be utilized to any suitable significant digit to the extent that a practical technical implementation may permit or require it. [0190] Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this technology belongs. Although any methods and materials similar or equivalent to those described herein can also be used in the practice or testing of the present technology, a limited number of the exemplary methods and materials are described herein.

[0191] When a particular material is identified as being used to construct a component, obvious alternative materials with similar properties may be used as a substitute. Furthermore, unless specified to the contrary, any and all components herein described are understood to be capable of being manufactured and, as such, may be manufactured together or separately.

[0192] It must be noted that as used herein and in the appended claims, the singular forms “a”, “an”, and “the” include their plural equivalents, unless the context clearly dictates otherwise. [0193] The term “about” is used herein to refer to quantities that vary by as much as 30%, preferably by as much as 20%, and more preferably by as much as 10% to a reference quantity. The use of the word “about” to qualify a number is merely an express indication that the number is not to be construed as a precise value.

[0194] All publications mentioned herein are incorporated herein by reference in their entirety to disclose and describe the methods and/or materials which are the subject of those publications. The publications discussed herein are provided solely for their disclosure prior to the filing date of the present application. Nothing herein is to be construed as an admission that the present technology is not entitled to antedate such publication by virtue of prior technology. Further, the dates of publication provided may be different from the actual publication dates, which may need to be independently confirmed.

[0195] The terms “comprises” and “comprising” should be interpreted as referring to elements, components, or steps in a non-exclusive manner, indicating that the referenced elements, components, or steps may be present, or utilized, or combined with other elements, components, or steps that are not expressly referenced. Thus, throughout this specification, unless the context requires otherwise, the words “comprise”, “comprises” and “comprising” will be understood to imply the inclusion of a stated step or element or group of steps or elements but not the exclusion of any other step or element or group of steps or elements. Any one of the terms: “including” or “which includes” or “that includes” as used herein is also an open term that also means including at least the elements/features that follow the term, but not excluding others. Thus, “including” is synonymous with and means “comprising”.

[0196] The various methods or processes outlined herein may be coded as software that is executable on one or more processors that employ any one of a variety of operating systems or platforms. Additionally, such software may be written using any of a number of suitable programming languages and/or programming or scripting tools, and also may be compiled as executable machine language code or intermediate code that is executed on a framework or virtual machine.

[0197] In this respect, various inventive concepts may be embodied as a processor readable medium or computer readable storage medium (or multiple such storage media) (e.g., a computer memory, one or more floppy discs, compact discs, optical discs, magnetic tapes, flash memories, circuit configurations in Field Programmable Gate Arrays or other semiconductor devices, or other non-transitory medium or tangible computer storage medium) encoded with one or more programs or processor control instructions that, when executed on one or more computers or other processors, perform methods that implement the various embodiments of the technology discussed above. The computer readable medium or media can be transportable, such that the program or programs stored thereon can be loaded onto one or more different computers or other processors to implement various aspects of the present technology as discussed above.

[0198] The terms “program” or “software” are used herein in a generic sense to refer to any type of computer code or set of computer-executable instructions that can be employed to program a computer or other processor to implement various aspects of embodiments as discussed above. Additionally, it should be appreciated that according to one aspect, one or more computer programs that when executed perform methods of the present technology need not reside on a single computer or processor, but may be distributed in a modular fashion amongst a number of different computers or processors to implement various aspects of the present technology. For example, some versions of the present technology may include a server with access to any of the computer readable or processor-readable mediums as described herein. The server may be configured to receive requests for downloading the processor- control instructions or processor-executable instructions of the medium to an electronic device, such as a smart mobile phone or smart speaker, over a network such as a communications network, an internet or the Internet. Thus, the electronic device may also include such a medium to execute the instructions of the medium. Similarly, the present technology may be implemented as a method of a server having access to any of the mediums described herein. The method(s) may include receiving, at the server, a request for downloading the processor- executable instructions of the medium to an electronic device over the network; and transmitting the instructions of the medium to the electronic device in response to the request. Optionally, the server may have access to the medium to execute the instructions of the medium.

[0199] Computer-executable instructions may be in many forms, such as program modules, executed by one or more computers or other devices. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Typically, the functionality of the program modules may be combined or distributed as desired in various embodiments.

[0200] Also, data structures may be stored in computer-readable media in any suitable form. For simplicity of illustration, data structures may be shown to have fields that are related through location in the data structure. Such relationships may likewise be achieved by assigning storage for the fields with locations in a computer-readable medium that convey relationship between the fields. However, any suitable mechanism may be used to establish a relationship between information in fields of a data structure, including through the use of pointers, tags or other mechanisms that establish relationship between data elements.

[0201] Although the technology herein has been described with reference to particular examples, it is to be understood that these examples are merely illustrative of the principles and applications of the technology. For example, although the acoustic generator(s) and acoustic monitoring techniques are described herein in particular examples concerning the use, and component s) of, RPT device(s), it will be understood that such acoustic generator(s) and acoustic monitoring techniques may be similarly implemented with the component(s) of any respiratory therapy (RT) device such as a high flow therapy (HFT) device that provides a controlled flow of air at therapeutic flow levels through a patient interface. Thus, the HFT device is similar to a pressure-controlled RPT device but configured with a controller adapted for flow control. In such examples, the acoustic generator(s) may be configured for measuring a gas characteristic associated with the high flow therapy generated by the HFT device and may be integrated to sample the gas flow of a patient circuit, a conduit coupler thereof, and/or a patient interface of the HFT device. Thus, the HFT device may optionally include an acoustic receiver, as well as the processing techniques for acoustic analysis as described herein, for receiving the acoustic/sound signal generated by the acoustic generator implemented HFT device.

[0202] In some instances herein, the terminology and symbols may imply specific details that are not required to practice the technology. For example, although the terms "first" and "second" may be used, unless otherwise specified, they are not intended to indicate any order but may be utilised to distinguish between distinct elements. Furthermore, although process steps in the methodologies may be described or illustrated in an order, such an ordering is not required. Those skilled in the art will recognize that such ordering may be modified and/or aspects thereof may be conducted concurrently or even synchronously.

[0203] It is therefore to be understood that numerous modifications may be made to the illustrative examples and that other arrangements may be devised without departing from the spirit and scope of the technology.