Field of Invention

The invention relates to simulation and/or monitoring of the supply or lack of supply of oxygen. Embodiments of the invention are preferably used in combination with a mannequin configured to mimic the physical characteristics of an animal (particularly human) subject, namely the airway and features of the body that impact on the airway.

Background

Mannequins have been designed and are commercially available for mimicking the characteristics of a patient. A subset of these have at least an artificial airway and lungs. An example of such a device is VBM Medizintechnik GmbH's- Airway Management Simulators "Bill I" (ref. no. 30-19-000), details on which can be found at http://www.vbm- medical.com/cms/files/kb vbm an sthesie 7.0 10.09 qb.pdf.

Prior art devices have limited functionality and cannot be used for the simulation of particular procedures. For example, prior art devices have limited, if any, capability for simulating "forced respiration" (i.e., a non-breathing patient) and/or monitoring parameters thereof. This would be useful to assess the performance of those attempting to practice procedures on such patients.

It is an object of the invention to provide for improved respiratory simulation and/or monitoring.

Alternatively, it is an object of the invention to at least provide the public with a useful choice. Summary of the Invention

According to a first aspect of the invention, there is provided a system for simulating and/or monitoring the supply of oxygen to a patient, the system including:

means for monitoring the pressure inside an airway and/or lungs (preferably an artificial airway and/or lungs); and

means for deriving an oxygen content of the bloodstream for a patient that would result from the detected pressure.

Preferably, the system includes a pressure sensor for detecting said pressure. Preferably, the system includes an artificial said airway and lungs.

Preferably, the means for deriving is communicatively coupled to the sensor to receive said pressure and derive said content. Preferably, the oxygen content is a measure of oxygen saturation.

Preferably, the means for deriving is configured to derive the oxygen content based on the algorithm set forth hereinafter in the section headed Detailed Description of Preferred Embodiments.

Preferably, the means for deriving is embodied or incorporated in an otherwise conventional laptop or PC-based computer.

Preferably, the system includes means for displaying one or more simulated parameters. According to preferred embodiments, the parameters include at least the simulated oxygen saturation.

Separate or the same means for displaying may be used to display performance related parameters. For example, a chart may be displayed which shows the variation of oxygen saturation against time.

Preferably, the system includes at least a partial mannequin having one or more anatomical features of a patient. Preferably, said mannequin includes at least a front portion of a neck.

Preferably, said front portion covers at least a portion of the airway.

Preferably, the front portion and/or the airway are configured to be incised to provide an opening therethrough. Such an opening is preferably able to be provided using conventional surgical equipment and may be used, for example, for the simulation of cricothyroidotomy or cricothyrotomy procedures. Further to this end, preferably, the system further includes a selectively closeable valve for blocking off at least a portion of the airway. Preferably, said valve is positioned between an open end of said airway (said open end being distal from said lungs) and said portion of the airway configured to be incised to provide an opening therethrough.

According to a second aspect of the invention, there is provided a method of simulating and/or monitoring the supply of oxygen to a patient, the method including:

monitoring the pressure inside an airway and/or lungs (preferably an artificial airway and/or lungs); and

deriving an oxygen content of the bloodstream for a patient that would result from the detected pressure.

Other aspects of the method of the invention are analogous to aspects of the system of the invention. More particularly, the method of the invention preferably includes one or more of the steps of the algorithm set forth hereinafter in the section headed Detailed Description of Preferred Embodiments.

According to a third aspect, the invention includes computer-readable instructions which when executed on a suitably enabled computing device performs one or more features of the method of the invention. This may include or be substituted by one or more steps of the algorithm set forth hereinafter in the section headed Detailed Description of Preferred Embodiments.

According to a fourth aspect, there is provided a mannequin configured for use in the system of the first aspect and/or the method of the second aspect and/or in combination with the computer-readable instructions of the third aspect.

The mannequin preferably includes at least an airway and lungs.

At least a portion of the airway may be configured to be incised for simulating procedures such as cricothyrotomy.

Preferably, the airway includes a valve for selectively closing the airway to provide a blockage. Such a valve may be used to simulate a blockage that would require a cricothyrotomy to be performed.

While the invention is generally described in terms of human treatments, it will be appreciated that the invention also readily applies to veterinary procedures and "patient" and similar terms are to be construed in a non-limiting manner.

Further aspects of the invention, which should be considered in all its novel aspects, will become apparent to those skilled in the art upon reading of the following description which provides at least one example of a practical application of the invention.

Brief Description of the Drawings

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

Figure 1 is schematic representation of an embodiment of the system of the invention; and Figure 2 shows an example display. Detailed Description of Preferred Embodiments

Monitoring aspects of the invention may be at least partly embodied in software which when executed by a suitably enabled computing device and configured to receive one or more inputs, monitors the simulated impact of actions on a patient. More particularly, the oxygen saturation and related physics parameters of a patient are determined based on inputs received from sensor(s) associated with an artificial airway, such as that of the aforementioned "Bill I" mannequin. For example, an external pressure sensor may be coupled to the computing device via a USB interface, the pressure sensor being attached to and measuring the pressure in a latex lung model of a patient that physically simulates the inhalation and exhalation cycle. A single pressure sensor connected to a small USB interface may provide a 10-bit pressure value (0-1024). Conventional computing equipment may be used as the computing device, including but not limited to PCs.

Embodiments of the invention track oxygen supply and oxygen consumption, preferably producing a readout on physiological parameters on a simulated instrument common to those found in the medical industry.

Forced respiration is similar to inflating a balloon. The amount of gas inside an inflatable bladder can be deduced by measuring the pressure difference between the inside and outside of the bladder. If the internal pressure is equal to the external pressure, the bladder must be substantially empty. When the internal pressure is higher than the external pressure, then there must be a certain amount of gas inside the bladder. Thus the pressure inside the bladder is a measure of the amount of gas present therein.

One can view the purpose of the lungs to remove the oxygen from an input gas stream and replace it with carbon dioxide. The respiration cycle completes with an exhalation after which a fresh oxygen rich gas can be inhaled. The pressure in the lungs changes during the breathing cycle.

According to particular embodiments, the pressure change over time is monitored as this is a measure of the amount of inhaled and exhaled gas. The oxygen content of the gas may be determined. For normal air, oxygen makes up about 21% of the stream. In medical environments, typically a 100% oxygen stream is supplied to a patient. Therefore with every pressure increase, oxygen rich gas is added to the remaining oxygen poor gas in the lungs. The ratio is a function of pressure change and can be used to track what the total oxygen percentage of the lungs is at any point in time.

A preferred algorithm of the invention takes virtual oxygen from the gas present in the lungs and supplies this to the blood at a certain rate. This produces the Sp02 percentage reading that reports the oxygen saturation in the blood. Sp02 is a measurement of the amount of oxygen being carried by red blood cells in the circulatory system. Sp02 is given as a percentage, and is typically around 96% in a healthy patient. Sp02 rises and falls dependent on how well a person is respiring and how well the circulation system is functioning.

In real life medical procedures, Sp02 may be measured using a device clipped onto a patient's finger. As will be appreciated, there is a time lag between the oxygen entering the lungs having an impact that is registered on the device since oxygen must travel from the lungs to the blood and then be circulated to the position of the device. This lag can be several seconds, whereby the Sp02 readout is behind what the actual value is. According to preferred embodiments, this lag is incorporated into the algorithm. The response of a patient to supplied oxygen depends on the patient's ability to take in oxygen. A range of parameters are available that control the more detailed aspects of the algorithm.

More detail relating to the algorithm of the invention will now be described.

According to preferred embodiments, levels of oxygen storage are considered since these can be used to determine the simulated Sp02. Firstly, the amount of oxygen stored inside the lungs is considered. This oxygen is absorbed and transferred to the blood, where it is consumed by the body as part of the respiration process. Both levels of supply and demand are relevant in order to calculate the simulated oxygen saturation in the blood.

The logic below may be used to determine state changes in time slices of 0.1 sec.

PartialOxygenPressure = (LungPressure ^* LungOxygenPercentage) / 100

OxygenAbsorbed = PartialOxygenPressure ^* OxygenAbsorbsionRate ^* 0.1 OxygenlnLungs = ((LungGassQuantity * LungOxygenPercentage) / 100) -

(OxygenAbsorbed)

LungOxygenPercentage = (OxygenlnLungs/LungGassQuantity) ^* 100 OxygenSaturation/ = OxygenSaturation _(M ) + (OxygenAbsorbed ^*

OxygenSaturationRecovery) - (OxygenConsumption * 0.1) where: LungPressure is a pressure value measured by the pressure sensor associated with the mannequin.

LungGassQuantity defines how much gas is assumed to be present in the lungs. Depending on the elasticity of the lungs and capacity, it is possible to make an assumption of how much volume of gas is represented by a measured pressure. This value is approximated by multiplying the LungPressure with an arbitrary factor that varies per patient.

OxygenlnLungs tracks how much oxygen remains in the lungs. During every respiration cycle, fresh air is added to the lungs and some stale air is exhaled. The software tracks this by tracking measured pressure changes (DeltaPressure) over a time slice. Oxygen content is defined for each pressure increase after which the new oxygen content is calculated. If DeltaPressure is positive, then: OxygenlnLungSj ₊ i = OxygenlnLungSj + (DeltaPressure * OxygenPercentage/100 *

PressureToVolumeFactor)

LungOxygenPercentage tracks how much of the gas in the lungs is oxygen. Atmospheric air for example contains 21% oxygen which will reduce over time when having entered the lungs as oxygen is replaced by carbon dioxide.

PartialOxygenPressure represents the pressure in the lungs caused by oxygen gas molecules and affects how fast oxygen can be absorbed by the lungs. As the percentage of oxygen reduces due to transfer to the blood this partial pressure reduces as well. Absolute pressure remains the same because oxygen is replaced by carbon dioxide.

Oxygen Absorbsion Rate defines how fast a particular patient can absorb oxygen. This is a measure of the rate of transfer of oxygen from the lungs to the bloodstream. OxygenAbsorbed defines the amount of oxygen transferred to the bloodstream during a given time slice or period. ^" Absorption is not constant and depends on the PartialOxygenPressure that reduces as more oxygen is used up.

OxygenSaturationRecovery defines how much effect a certain amount of oxygen has on a patient's OxygenSaturation. This varies per patient and is dependent on blood quantity and other physiological parameters.

OxygenConsumption defines the rate at which oxygen is consumed by the body. A body in rest uses less oxygen than a body that is exercising. Consumption here is simply expressed as a percentage which may vary between time slices. OxygenSatu ration defines the percentage of oxygen in the bloodstream, with / ^' and (/-1) notations indicative of determinations of successive time instances. The body consumes oxygen stored in the blood. Again this is a matter of supply and demand.

The algorithm preferably includes the aforementioned delay feature that better ensures that the reading on the simulated OxygenSaturation detector is, say, reported 5 seconds later to account for the oxygen enriched blood taking some time to move from the lungs to the fingertip where typically the OxygenSaturation sensor is placed. The delay is preferably user configurable.

Simulated digital instruments and audio signals may replicate the workings of standard medical monitoring equipment while a graph plotter can be used to review performance (e.g. by plotting OxygenSaturation against time to ensure it remains at acceptable levels).

A schematic representation of the apparatus and system of the invention is provided in Figure 1. The system 1 shown in Figure 1 includes mannequin 10, sensor 16, computing device 18 and display 20. Mannequin 10 may include a conventional medical mannequin, such as the aforementioned

Bill I mannequin, which includes at least airway 12 and lungs 14 formed from inflatable bladders or balloons. As will be appreciated, additional features can be added to improve realism and/or the suitability of the mannequin 10 for additional procedures. For example, an artificial mouth and/or nose may be provided at the end of the airway 12 distal from the lungs 14.

According to a presently preferred embodiment, the neck of a Bill I mannequin was modified to improve anatomical accuracy. Further, a new surface was provided therefor from a specially designed silicon sheet. Under this a new "larynx" or surface therefor was designed to provide the correct anatomy. This was connected to customised tubing which represented the trachea and was joined to 500ml breathing bags to simulate the lungs. The replacement throat and tubing provided for improved simulation of cricothyrotomy procedures, as well as replacement thereof following such procedures. The upper airway was connected to a narrow tube and a "three-way-tap" 22 which simulated an upper airway obstruction. During a cricothyrotomy procedure, an incision is made in the artificial larynx 24 below the obstruction. To reduce operational costs, the portion configured to be incised may be sheet of material bonded to or otherwise coupled to an open portion of the airway or the portion may form a part of the airway (i.e., be essentially tubular), such that only a portion of the airway requires replacing after incision.

The "trachea" tubing had a side port connected to sample tubing. This sample tubing was connected to a pressure sensor (i.e. the sensor 16), which generates an electronic signal for output to a computing device such as a PC or laptop computer. This signal was representative of the pressure inside the lungs 14. It will be appreciated that sensor 16 could be shown as being incorporated within mannequin 10. Furthermore, one or more intermediary or additional devices may be used, as desired to store and/or transmit the data to a computer, including one remote from the mannequin 10. Any data communication described herein may be effected using any known forms of wired or wireless communications.

Software, preferably executed on computing device 14 (or elsewhere provided suitable data connections are provided) simulated fluctuating oxygen saturation levels. This software responded to a pressure signal which was generated whenever positive pressure ventilation occurred down the model trachea. This positive pressure would be a signal to the algorithm to reverse a trend of dropping oxygenation. The effect of the change was preferably determined as set out hereinbefore.

In the event of failed ventilation, a drop in oxygenation levels is simulated. Similarly, if the mannequin was successfully ventilated via, say, emergency transtracheal ventilation, the decline in oxygenation would be reversed, and the oxygen levels would return to normal. As stated previously, the key variable being measured is airway pressure, which is the proxy measure for oxygenation. Consequently, as the detected pressure increases, the oxygen pressure increases, indicating successful transtracheal ventilation. Otherwise, the oxygen pressure decreases as it is used up and replaced with carbon dioxide.

An example display 20 according to the invention is provided in Figure 2. It will be appreciated that appropriately configured hardware could be used, but preferred embodiments present the display 20 as a window on a computer display, such as that associated with computing device 18. However, separate or remote displays may additionally or alternatively be used.

Thus, the invention provides a simulator that simulates and measures oxygen supply to a non-breathing person. A wide range of procedures can be performed on this simulator since the device uses a pressure sensor attached to a mannequin. Such procedures depend on mannequin configuration and include but are not limited to:

- cricothyrotomy (forced or natural breathing)

- Mouth-to-mouth

- Breathing assistance using a bag or other equipment

Unless the context clearly requires otherwise, throughout the description and the claims, the words "comprise", "comprising", and the like, are to be construed in an inclusive sense as opposed to an exclusive or exhaustive sense, that is to say, in the sense of "including, but not limited to".

The entire disclosures of all applications, patents and publications cited above and below, if any, are herein incorporated by reference.

Reference to any prior art in this specification is not, and should not be taken as, an acknowledgement or any form of suggestion that that prior art forms part of the common general knowledge in the field of endeavour in any country in the world.

The invention may also be said broadly to consist in the parts, elements and features referred to or indicated in the specification of the application, individually or collectively, in any or all combinations of two or more of said parts, elements or features.

Wherein the foregoing description reference has been made to integers or components having known equivalents.thereof, those integers are herein incorporated as if individually set forth.

It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the invention and without diminishing its attendant advantages. It is therefore intended that such changes and modifications be included within the scope of the invention.