Technical Field

The invention relates to a method and apparatus for calculating and displaying a respiratory rate using a hand-portable measurement apparatus.

Background to the Invention

A respiratory rate is the number of breaths taken within a set amount of time. Respiratory rate can also be known as respiration rate, pulmonary ventilation rate, ventilation rate, or breathing frequency.

Human respiration rate is measured when a person is at rest and involves counting the number of breaths taken by the person during a set amount of time, typically 60 seconds. A rise and fall of the person's chest indicates a single breath.

A normal respiratory rate is termed Eupnoea. For an adult human, the average respiratory rate is between 8 and 20 breaths per minute. An above normal respiratory rate is termed Tachypnea and a below normal respiratory rate is termed Bradypnea. A respiratory rate above or below this average may indicate a medical condition. Abrupt changes of the respiratory rate, even if within the average range, may also indicate a medical condition. The medical condition may be a fever, for example, or other illness.

Respiratory rates vary according to age: babies below 1 year of age average 30 to 40 breaths per minute, children between 1 and 3 years of age average 23 to 35 breaths per minute, children between 3 and 6 years of age average 20 and 30 breaths per minute, children between 6 and 12 years of age average 18 to 26 breaths per minute, and children between 12 and 17 years of age average 12 to 20 breaths per minute. Current methods of measuring respiration rates by nurses, or other medical practitioners, involve using a watch or other clock to measure a set period of time (usually one minute) and counting the number of breaths taken by a subject during the period of time. This can be inaccurate as the timing and/or counting may not be precise as the practitioner has to monitor both the movement of the chest of the subject and also the clock.

The standard measure of respiratory rate is breaths per minute, therefore, the number of breaths counted by the practitioner within one minute is the measured rate, i.e. no calculation needs to be performed on the number of breaths counted to reach the respiratory rate per minute.

Summary of the Invention

Embodiments of the invention relate to medical monitoring equipment and, specifically, to respiratory rate measuring systems. An apparatus and corresponding method to calculate a respiration rate of a person is described, which operates by the user observing the breathing of a patient, and activating a breath counter, for example by touching a touchscreen, or pressing a button provided on the device, upon the incidence of each breath. A timer in the device measures the period over which the inputs are made, and the computing device is then subsequently able to calculate a display a breathing rate for the patient. The apparatus is intended to be used and the method performed where monitoring or respiratory rate is required, such as a hospital or care home.

In view of the above a first aspect of the invention provides a method of measuring respiratory rate with a hand-portable apparatus having at least one manual input, comprising: counting a plurality of discrete input activations of the manual input by a user, the discrete input activations occurring when the user discerns a subject whose respiratory rate is being measured to undertake a breath; determining a measurement period over which the input activations occurred; and calculating a respiratory rate for the subject in dependence on the count of discrete input activations, and the determined length of the measurement period.

The measurement period is the period over which the input activations occur. The measurement period begins and ends with a discrete input corresponding to an inhalation, an exhalation, or both. No part of the measurement period relates to a period before a first user input or after a final user input. The method of the prior art uses a fixed period of time and a number of breaths within which are counted. In the prior art, the fixed period begins and the user must wait for an inhalation or exhalation before counting a breath. This initial period of waiting does not correspond to a whole measured breath and the duration of the initial period will depend on the point in the breathing cycle of the patient at which the fixed period begun. A final period of waiting will occur after a final breath is counted during the fixed period, but prior to the end of the fixed period. The lengths of the initial and final periods will vary and the presence of either or both decreases the accuracy of a result achieved using the prior art method. Embodiments of the invention do not take account of such an initial or final period, and hence provide a more accurate respiratory rate measurement method compared to the prior art. Further, the duration of the initial and final periods of the prior art method are not dependent upon the duration of the fixed period, therefore, the accuracy of a respiration rate calculated using the prior art method can only be increased by increasing the duration of the fixed period, thereby reducing the inaccuracies introduced by the initial and final periods. Embodiments of the present invention have no such disadvantages.

By undertaking a breath we mean when the subject either inhales, exhales, or both, provided that the input activations are consistent from breath to breath. For example, if the user undertakes a discrete input activation when the user begins to inhale, then the user should continue to undertake discrete input activations for subsequent breaths at the start of inhalation. Similarly, if the user undertakes a discrete input activation between inhalation and start of exhalation then the user should continue to undertake subsequent discrete input activations at the same point for subsequent breaths. Likewise, if the user undertakes a discrete input activation at the end of exhalation, then the user should again continue to undertake subsequent discrete input activations at the same point for subsequent breaths. Generally, the discrete input activation should be undertaken at the same point in each breath cycle i.e. the same point in each inhalation -exhalation cycle to ensure accuracy.

Where the user undertakes a discrete input activation upon both an inhalation and an exhalation, then two activations will be performed for each breath. To find the count of the actual number of breaths observed, the number of discrete input activations should be divided by two in such circumstances.

Preferably, the number of discrete inputs is pre-determined. The number of breaths counted is pre-determined to provide a sufficient amount of data to provide a required level of accuracy of the calculated respiratory rate. A greater number of breaths counted provides a more accurate result, but the result will take longer to be determined. Preferably, the number of discrete inputs is between three and ten, inclusive. It has been established that measuring the duration of three breaths provides an adequately reliable respiratory rate which is achieved quickly, relative to the method of the prior art. It has also been established that little accuracy is gained if more than ten breaths are measured.

Preferably, the measurement period begins at a first discrete input and ends at a last discrete input. This ensures that no time is accounted for during the measurement period which is not between breaths. This increases the accuracy of the calculated respiratory rate.

Preferably, the respiratory rate Vfm in terms of breaths per minute is calculated using:

Vfm = (60 ÷ measurement period) x (count - 1) where "count" is the number of discrete input activations entered by the user.

Prior art methods require measurements to be determined over a predetermined amount of time to provide an average per minute. The present method allows counting of any number of breaths to accurately calculate a respiratory rate per minute. Preferably, the manual input is a touch- screen, having a defined activation area to receive the discrete input activations of the user. The defined area allows the user to selectively provide an input into the method and also use an area of the touch-screen, other than the defined activation area, for other purposes not related to the method.

Preferably, the method further comprises displaying the calculated respiratory rate on a display of the hand-portable apparatus. The user can instantly determine whether or not further action is required relating to the subject, or whether the calculated respiratory rate should be re-measured using the method and the respiratory rate be subsequently re-calculated.

Preferably, the method further comprises determining a temporal variability of the discrete input activations during the measurement period, the determined temporal variability indicating a reliability of the measurement. Preferably, the temporal variability is determined by measuring the time between respective input activations, wherein if the respective time measurements differ by greater than a threshold amount, then it is determined that the measurement is unreliable.

A reliability measurement enables a user to decide whether or not to re-measure the measured respiratory rate. Should the reliability measurement indicate that the measurement is unreliable, the apparatus may not accept the measurement and insist of a repeat measurement.

Preferably, the user input activation is a tap on the manual input. A tap allows the user to provide an input of short duration, which enables the time of the input to be accurately established and also for another input to be registered in quick succession.

A second aspect of the invention provides a hand-portable apparatus for measuring respiratory rate, the apparatus comprising: a manual input arranged to detect a discrete input activation from the user; a display, and a processor, arranged to cause the apparatus to: count a plurality of discrete input activations of the manual input by the user, the discrete input activations occurring when the user discerns a subject whose respiratory rate is being measured to undertake a breath; determine a measurement period over which the input activations occurred; and calculate a respiratory rate for the subject in dependence on the count of discrete input activations, and the determined length of the measurement period. Preferably, the number of discrete inputs is pre-determined in length.

Preferably, the number of discrete inputs is three or more.

Preferably, the number of discrete inputs is ten or fewer.

Preferably, the measurement period begins at a first discrete input and ends at a last discrete input.

Preferably, the respiratory rate Vfm in terms of breaths per minute is calculated using:

Vfm = (60 ÷ measurement period) x (count - 1)

Preferably, the manual input is a touch- screen, having a defined activation area to receive the discrete input activations of the user.

Preferably, the calculated respiratory rate is displayed on the display of the hand- portable apparatus. Preferably, the processor is further arranged to determine a temporal variability of the discrete input activations during the measurement period, the determined temporal variability indicating a reliability of the measurement.

Preferably, the temporal variability is determined by measuring the time between respective input activations, wherein if the respective time measurements differ by greater than a threshold amount then it is determined that the measurement is unreliable. Preferably, the user input activation is a tap on the manual input.

The above features of the second aspect have similar advantages to those of the corresponding features of the first aspect.

A third aspect of the invention provides a method of measuring patient respiratory rate using a hand-portable measurement apparatus provided with a manual input arranged to detect discrete user activations, and a display for displaying calculated respiratory rate, the method comprising: observing a patient subject, and starting a measurement period by performing a first discrete activation of the manual input when it is observed that the patient undertakes a breath; continuing to observe the patient subject, and performing one or more further discrete activations of the manual input each time when it is observed that the patient undertakes a breath; and ending the measurement period by performing a last discrete activation of the manual input when it is observed that the patient undertakes a final breath to be measured; and viewing the calculated respiratory rate on the display.

The method using the hand-portable measurement apparatus allows increased accuracy of calculated respiratory rates by allowing inhalation and exhalation by the patient to be monitored closely as manual tasks of counting, timing and performing calculations are automated. The variable breath count allows for the respiratory rate of the patent to be calculated more quickly than was previously available.

Preferably, the number of discrete inputs is ten or fewer. The above features of the third aspect have similar advantages to those of the corresponding features of the first aspect.

Description of the Drawings

The invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

Figure 1 is a schematic view of a computing device;

Figure 2 is a flow chart; and Figure 3 is a Graphical User Interface (GUI) imposed onto a handheld computing device.

Description of the Embodiments

Figure 1 shows a schematic view of a computing device 100. The computing device 100 has a number of subsystems. A data bus 101 is a subsystem which transfers data between other subsystems of the device 100. Other subsystems include a processor 102, which is an electronic circuit that executes computer programs; a display adapter 103, which generates a feed of output images and provides them to a display 104; a section of Random Access Memory (RAM) 105, which is memory that can be read from and written to in arbitrary sequence; a section of Read-Only Memory (ROM) 106, which is used to store a piece of firmware, which is a control program for the device 100; a external bus interface 107 for interfacing small peripheral devices with the computing device 100; and a file system 108, which contains an operating system computer program, application computer programs that can be accessed by the operating system, and data files.

The processor 102 can send data to and receive data from a wireless network interface 109. The wireless network interface 109 can transmit and receive data wirelessly over a Wireless Local Area Network (WLAN), and uses protocols such as Wi-Fi™ and Bluetooth™ (IEEE 802.11 standards).

The processor 102 also connects to a user input device 110 which receives data from user input devices and translates the data into a form which the microprocessor can interpret. A push button 111 forms a first user input device and a touch screen 112 forms a second user input device. The touch screen 112 and the display 104 are incorporated into a display component 120 and the touch screen can detect the presence and location of a touch from an external object or user within the display area of the display 104.

The computing device 100 can be either in the form of a static unit, such as a desktop computer, which is not portable; or a portable unit, such a laptop, a tablet (as shown in Figure 3), a phone, or other portable computing device. Figure 2 shows a flowchart of a computer program which can be stored and run on a computing device such as that shown in Figure 1. The method of Figure 2 begins at step START 201. After which, counter values A, TIMER are initialised to zero at step 202.

At step 203, the method evaluates if the screen of the touch screen device has been touched. If not, the method returns to step 203. If the touch screen has been touched, the method progresses to step 204.

A timer is started at step 204 and the elapsed time of the timer corresponds to the value TIMER. The method progresses to step 205 where the location of the screen touch detected at step 203 is evaluated to see whether or not the touch was within a predetermined area of the screen.

At step 205, if the touch was outside the predetermined area, the method proceeds to step 206 where the touch is processed. Step 206 will either ignore the touch and return to step 203 if the touch did not correspond to a valid user input, alternatively step 206 will progress to step 209 if the touch corresponds to a user input to end the method. Step 209 will end the timer TIMER and the method will calculate a respiration rate at step 210, as described below, before the method ends by progressing to step 211. At step 205, if the touch was inside the predetermined area, the method proceeds to step 207 where counter A is incremented. The method then progresses to step 208 where the value of A is compared to a predetermined variable MAX_A. If A does not equal MAX_A, the method returns to step 203. If A does equal MAX_A, the method progresses to step 209 ending TIMER.

After step 209, the method progresses to step 210 where the respiratory rate per minute Vfm is calculated by dividing sixty by the value of TIMER (the elapsed time) in seconds and multiplying the result by the value of A (number of touches within the predetermined area) minus one. The calculation is represented as:

Vfm = (60 ÷ TIMER) x (A - 1) Eqn. 1 the calculated Vfm is displayed to a user of a device performing the method.

MAX_A is set to a value of the number of breaths to be recorded, plus one. For example, if five breaths are to be recorded, MAX_A equals 6. A first touch starts TIMER and A will be incremented to one. After five breaths are recorded, corresponding to five touches within the predetermined area, A equals six. The value of timer corresponds to 20 seconds. From equation 1,

Vfm = (60 ÷ 20) x (6 - 1) giving a respiratory rate per minute of 15.

In the embodiment shown in Figure 2, step 210 is executed immediately prior to the end of the method. In another embodiment, step 210 is executed after step 203 when the screen has not been touched. This embodiment provides a constant updating respiration rate calculation.

As described previously, the user should be consistent in timing from breath to breath as to when in the breathing cycle of the subject a breath is recorded. For example, if the user undertakes a discrete input activation when the subject begins to inhale, then the user should continue to undertake discrete input activations for subsequent breaths at the start of inhalation. Similarly, if the user undertakes a discrete input activation between inhalation and start of exhalation of the subject then the user should continue to undertake subsequent discrete input activations at the same point for subsequent breaths. Likewise, if the user undertakes a discrete input activation at the end of exhalation of the monitored subject, then the user should again continue to undertake subsequent discrete input activations at the same point for subsequent breaths. Generally, the discrete input activation should be undertaken at the same point in each breath of the subject i.e. the same point in each inhalation - exhalation cycle to ensure accuracy.

In yet another embodiment, a method includes the above steps and also calculates a reliability measurement of the calculated average respiratory rate. The calculation of the reliability measurement may include calculating a variance or a standard deviation using the time periods between touches within the predetermined area, or calculating a correlation of time periods between touches within the predetermined area. The calculation of the reliability measurement may also include evaluating the periods between consecutive user inputs. The regularity of the periods are determined and if the periods are irregular by more than a certain amount or percentage, the reliability of the calculated average is reduced.

In a further embodiment, the number of breaths to be measured is not predetermined. The measurement period is started by a user registering a touch within the predetermined area and the user continues to register touches corresponding to breaths of a subject for a number of breaths of the user's choosing. The user then registers a final input. The value of the timer user for calculating the respiration rate is the value of the timer when the last breath was registered.

In a yet further embodiment, a physical button is used to register a user input and is used as an input to increment the counter.

Figure 3 shows a GUI displayed by a tablet device 300 running a computer program. The tablet device 300 has a touch screen 301 for both displaying the GUI and receiving user input. A button 302 is located on the tablet device 300 below the touch screen 301.

The GUI has a receptive area 304, which is for inputting data relating to breaths taken. A close program icon 303 is located at an upper right portion of the GIU and a user input within this area will provide a command to close the application running the GUI.

Three further areas of the GUI display more information. These three areas are located above the receptive area 304 and are at an upper left portion of the GUI. A first 305 of these three information areas displays timer information, i.e. how long the current counting of breaths has been performed for. A second information area 306 displays count information, i.e. how many breaths have been counted while the timer 305 has been running. A third information display area 307 displays an averaged respiration rate per minute for the current timed measurement of breaths.

A finger 308 is shown drawn using a broken line over the receptive area 304. If the finger 308, or any other object which the touch screen 301 is receptive to, contacts the touch screen 301 within the receptive area 304, a breath will be registered and the number displayed in the count information display box 306 will increment. The averaged respiration rate displayed by the third display area 307 will be continually updated while the timer 305 is running and breaths are being counted.

In another embodiment, the GUI displays further display areas with other information shown. The other information may include a reliability measurement of the data being presented.

Various other modifications, whether by addition, deletion, or substitution may be made to the above described embodiments to provide further embodiments, any and all of which are intended to be encompassed by the appended claims.