WO2002041777A1

WO2002041777A1 - A device for converting a characteristic of a flowing fluid into an electronic signal and a respiratory monitor for monitoring fluid flow

Info

Publication number: WO2002041777A1
Application number: PCT/IE2001/000145
Authority: WO
Inventors: Marilyn Frances Lennon; Jan Mikael Fernstrom; Mark Marshall
Original assignee: University Of Limerick
Priority date: 2000-11-21
Filing date: 2001-11-21
Publication date: 2002-05-30
Also published as: IES20011006A2; AU2002223975A1

Abstract

A device (1) for converting the flow rate of a flowing fluid intoan electronic signal indicative of the flow rate comprises a tubular member (2) having a bore (3) extending between an upstream end (5) and a downstream end (6) through which the flowing fluid is passed. A deformable resilient membrane (8) is located in thebore (3) an is deformable in response to the rate at which the fluid is flowing. The membrane (8) is of a piezo electric materialwhich outputs an analogue voltage signal proportional to the amount of bending of the membrane (8). The voltage signal is outputted on a cable (16) an may be used in its analogue form or converted to a digital signal for relaying to a computer for in turn displaying a graphical representation of the flow rate of the fluid on a monitor. The device (1) may also be used for training a subject to breath correctly by displaying a graphical representation of the flow rate of air being inhaled and exhaled by the subject during breathing against a graphical representation of the flow rate of an ideal breathing cycle.

Description

"A device for converting a characteristic of a flowing fluid into an electronic signal and a respiratory monitor for monitoring fluid flow"

The present invention relates to a device for converting a characteristic of a flowing fluid into an electronic signal indicative of the characteristic of the flowing fluid. The invention also relates to a monitoring device for monitoring fluid flow, and to a respiratory monitor for monitoring a breathing cycle of a subject, and the invention also relates to a method for training a subject in breathing.

It is important that people breathe correctly. While all people breathe, many do not breathe correctly, and in particular, many do not fully exercise their lungs during a breathing cycle. This is particularly so in the case of people who suffer from respiratory ailments, for example, asthma, bronchitis and the like. Such subjects in many cases breathe irregularly and in general do not exercise their lungs to the full extent, thus resulting in relatively shallow breathing. This is undesirable, and indeed, exacerbates the ailment from which they suffer.

There is therefore a need for a respiratory monitor for monitoring breathing of a subject and there is also a need for a method for facilitating training a subject in breathing. Indeed, there is a need for a device and a method for monitoring a characteristic of a flowing fluid, be it air or other fluid, whether related to breathing or not.

The present invention is directed towards providing a device for converting a characteristic of a flowing fluid into an electronic signal. The invention is also directed towards providing a monitoring device for monitoring a characteristic of a flowing fluid, as well as to a respiratory monitor for monitoring respiration of a subject, and the invention is also directed towards use of the respiratory monitor and to a method for training a subject to breathe.

According to the invention there is provided a device for converting a characteristic of a flowing fluid into an electronic signal indicative of the characteristic of the flowing fluid, wherein the device comprises a body member defining a fluid accommodating passageway extending therethrough for accommodating the flowing fluid, a deformable membrane extending into the passageway and generally transversely thereof, the membrane being deformable by the flowing fluid, the amount of deformation being proportional to the characteristic of the flowing fluid, and a sensing means for detecting the amount of deformation of the membrane for converting the amount of deformation of the membrane into the electronic signal and for outputting the electronic signal indicative of the characteristic of the flowing fluid.

In one embodiment of the invention the electronic signal outputted by the sensing means is proportional to the amount by which the membrane is deformed.

In another embodiment of the invention the membrane is a resilient membrane. Preferably, the membrane is an elongated membrane extending from a first end to a second end and being secured to the body member adjacent the first end thereof, the second end being located in the passageway. Advantageously, the second end of the membrane is a free end. Ideally, the membrane is deformable by bending intermediate its first and second ends, and preferably, the membrane is deformable over its entire length in the passageway.

In one embodiment of the invention the fluid accommodating passageway is formed by a fluid accommodating bore extending through the body member. Preferably, the membrane extends transversely across the fluid accommodating bore.

In one embodiment of the invention the membrane is secured at one side of the fluid accommodating bore and extends transversely across the bore to the other side thereof. Preferably, the free end of the membrane is spaced apart from the body member.

In one embodiment of the invention the area of the membrane presented to the flowing fluid is at least 50% of the transverse cross-sectional area of the fluid accommodating bore, and preferably, the area of the membrane presented to the flowing fluid is at least 75% of the transverse cross-sectional area of the fluid accommodating bore. In one embodiment of the invention the fluid accommodating bore is of circular transverse cross-section.

In another embodiment of the invention the membrane defines a pair of spaced apart side edges extending between the respective first and second ends. Preferably, the respective side edges defined by the membrane extending between the first and second ends extend parallel to each other. Advantageously, the area of the membrane presented to the flowing fluid through the fluid accommodating bore is of rectangular shape.

In one embodiment of the invention the membrane extends into the passageway through a slot formed in the body member. Preferably, the membrane is sealably secured in the slot in the body member.

In another embodiment of the invention the sensing means comprises a piezo electric sensing means. Preferably, the piezo electric sensing means comprises a piezo electric film. Advantageously, the membrane is formed by the piezo electric film. Ideally, the membrane comprises a pair of piezo electric sheets laminated together to form the film. Preferably, the respective piezo electric sheets are of opposite polarities, and are laminated together to form the film. Advantageously, the piezo electric film is a film which is sold under the Trade Mark KYNAR.

In one embodiment of the invention the electronic signal outputted by the sensing means is an analogue signal.

In another embodiment of the invention the device comprises an analogue to digital converter for converting the analogue output signal from the sensing means to a digital signal suitable for inputting to a computer for further processing.

In one embodiment of the invention the characteristic of the flowing fluid to be converted to the electronic signal is the flow rate of flowing fluid through the passageway. In another embodiment of the invention the device is adapted for monitoring breathing of a subject, and the characteristic being monitored is the flow rate of air being inhaled and/or exhaled by the subject during an inspiratory phase and/or an expiratory phase, respectively, of a breathing cycle.

In a further embodiment of the invention a communicating means is provided for communicating the fluid accommodating passageway with the subject so that air being inhaled by the subject during the inspiratory phase and/or being exhaled during the expiratory phase of a breathing cycle passes through the passageway. Preferably, the communicating means comprises a face mask adapted to communicate with the mouth of the subject. Alternatively, the communicating means comprises a face mask adapted to communicate with the nose of the subject.

In another embodiment of the invention the communicating means comprises a face mask adapted to communicate with the mouth and the nose of the subject.

In a further embodiment of the invention the communicating means comprises a face mask adapted to alternately communicate with the nose and the mouth of the subject during inspiratory and expiratory phases, respectively, of a breathing cycle.

In a still further embodiment of the invention the passageway communicates with atmosphere for facilitating inhaling and exhaling of air by the subject through the fluid accommodating passageway of the device.

Additionally the invention provides a monitoring device for monitoring a characteristic of a flowing fluid, the monitoring device comprising the device according to the invention for converting a characteristic of the flowing fluid into an electronic signal indicative of the characteristic of the flowing fluid, and a reading means for reading the electronic signal outputted by the device.

Further the invention provides a respiratory monitor for monitoring respiration of a subject, the respiratory monitor comprising a device according to the invention, and a communicating means communicating the fluid accommodating passageway of the device with the mouth and/or nose of the subject.

In one embodiment of the invention a storing means is provided for storing a representation of a characteristic of at least one reference breathing cycle, a computing means for computing the characteristic from signals received from the device, and a display means for simultaneously displaying the computed characteristic and the reference characteristic for facilitating visual comparison of the computed characteristic with the reference characteristic.

In another embodiment of the invention the stored reference breathing cycle comprises a graphical representation of the characteristic, and the computed characteristic comprises a graphical representation of the computed characteristic.

In another embodiment of the invention the graphical representation of the reference breathing cycle comprises a graphical representation of the flow rate of inhaled and exhaled air during an inspiratory phase and an expiratory phase of the reference breathing cycle plotted against time. In a further embodiment of the invention the computed characteristic is a graphical representation of the flow rate of inhaled and exhaled air of the subject during the inspiratory phase and expiratory phase of a breathing cycle plotted against time.

Preferably, the graphical representation of the flow rate of inhaled and exhaled air during the inspiratory and expiratory phases of a breathing cycle plotted against time is plotted against real time and is displayed in real time.

In one embodiment of the invention the display means comprises a visual display monitor.

In another embodiment of the invention the computing means comprises a microprocessor. In a further embodiment of the invention the storing means comprises a non-volatile random access memory. The invention also relates to use of the respiratory monitor according to the invention for training a subject how to breathe by facilitating a visual comparison between a breathing cycle of the subject and a reference breathing cycle. Preferably, the visual comparison is facilitated by simultaneously displaying a graphical representation of the reference breathing cycle and the graphical representation of the breathing cycle of the subject. Advantageously, the respective graphical representations of the breathing cycles are graphical representations of the flow rates of inhaled and exhaled air during the respective inspiratory and expiratory phases of a breathing cycle.

Further the invention provides a method for training a subject to breathe, the method comprising the steps of monitoring a characteristic of the breathing of the subject during a breathing cycle and comparing the monitored characteristic with a corresponding characteristic of a reference ideal breathing cycle.

In one embodiment of the invention the method comprises graphically representing the characteristic of breathing of the subject during the breathing cycle and graphically representing the characteristic of the reference breathing cycle.

In another embodiment of the invention the graphical representation of the characteristic of the reference breathing cycle and the graphical representation of the characteristic of breathing of the breathing cycle of the subject are simultaneously displayed.

Advantageously, the graphical representation of the characteristic of breathing of the breathing cycle of the subject is displayed in real time.

In one embodiment of the invention the characteristic is the flow rate of inhaled and exhaled air during the respective inspiratory and expiratory phases of a breathing cycle.

The invention will be more clearly understood from the following description of some preferred embodiments thereof, which are given by way of example only, with reference to the accompanying drawings, in which: .

Fig. 1 is a perspective view of a device according to the invention for converting a characteristic of a flowing fluid into an electronic signal indicative of the characteristic,

Fig. 2 is an end elevational view of the device of Fig. 1,

Fig. 3 is another perspective view of the device of Fig. 1 ,

Fig. 4 is a perspective view of another detail of the device of Fig. 1 ,

Fig. 5 is a circuit diagram of the device of Fig. 1 ,

Fig. 6 is a partly block representation of a respiratory monitor according to the invention for monitoring breathing of a subject, and

Fig. 7 is a graphical representation of a display of the monitoring device of Fig. 6.

Referring to the drawings and initially to Figs. 1 to 5, there is illustrated a device according to the invention indicated generally by the reference numeral 1 for converting a characteristic of a flowing fluid into an electronic signal indicative of the characteristic of the flowing fluid. In this embodiment of the invention the characteristic is the flow rate of the flowing fluid. The device 1 is particularly suitable for measuring the flow rate of air, for example, air inhaled and exhaled by a subject during the inspiratory and expiratory phases of a breathing cycle.

The device 1 comprises a body member formed by an elongated tubular member 2 which defines an elongated bore 3 of circular transverse cross-section extending from an upstream end 5 to a downstream end 6 which forms a passageway for accommodating air or other fluid, the flow rate of which is to be monitored. A communicating means comprising a flexible tube (not shown in this embodiment of the invention) extends from the upstream end 5 of the tubular member 2, and terminates in a suitable adapter for communicating with the subject, for example, a mouth and/or nasal mask (not shown) so that inhaled and exhaled air during the inspiratory and expiratory phases of each breathing cycle of the subject passes through the bore 3 of the device 1. The downstream end 6 of the bore 3 is open to atmosphere. Although the end 5 of the tubular member 2 has been referred to as the upstream end, and the end 6 has been referred to as the downstream end, the use of the terms "upstream" and "downstream" is not intended to give an indication of the direction of flow of fluid through the bore 3, since the direction of flow will change depending on whether the subject is breathing in the inspiratory or expiratory phase of a breathing cycle.

A deformable membrane 8, which is deformable in response to the rate of flow of air flowing through the bore 3 extends into and transversely across the bore 3. In this embodiment of the invention the membrane 8 comprises a pair of piezo electric sheets of opposite polarity which are laminated together to form a piezo electric film. Such piezo electric films are sold under the Trade Mark KYNAR. The piezo electric film provides an output voltage which is proportional to the amount of deformation of the membrane 8. The membrane 8 is an elongated membrane extending between a first end 10 at which the membrane is anchored and secured in the tubular member 2 and a second end, namely, a free end 11 which is free to move in the upstream or downstream direction within the bore 3 as the membrane 8 is deformed by air flowing through the bore 3. The membrane 8 extends into the bore 3 through a slot 12 in the tubular member 2, and is sealably secured in the slot 12. The membrane 8 is substantially rectangular in shape defining respective parallel side edges 14 which extend between the respective first end 10 and the free end 11. In this embodiment of the invention the area of the membrane 8 which is presented to air flowing through the bore 3 when the membrane 8 is undeformed is approximately 75% of the transverse cross-sectional area of the bore 3. The membrane 8 is resilient and forms a bending element or a "bimorph", and since the membrane 8 is of a piezo electric material, the membrane 8 acts as a sensing means which outputs an analogue electronic signal, namely, a voltage proportional to the degree of bending of the membrane 8 between its first end 10 and its free end 11. The degree to which the membrane 8 bends is proportional to the rate of flow of the air through the bore 3, and thus the output voltage is proportional to the flow rate of air through the bore 3. Electrical connections (not shown) are made to the membrane 8 in a sub-housing 15 from which the membrane 8 extends into the bore 3, and a two-wire cable 16 from the connections (not shown) outputs the voltage which is proportional to the amount of bending of the membrane 8.

The electronic signal from the cable 16 is relayed to an analogue-to-digital converter 20 which converts the analogue signal from the membrane 8 to a digital signals which appears across an output terminal 21 and a ground terminal 22 of the analogue-to-digital converter 20. The analogue to digital converter 20 is powered by applying an appropriate power supply across the ground terminal 22 and a power supply terminal 23. The digital signal from the analogue to digital converter may be relayed to a computer, for example, a personal computer. The computer could be appropriately programmed to provide a graphical representation of airflow through the bore 3 on a visual display monitor of the computer. Additionally, suitable software in the computer may be provided for monitoring the air flow through the bore 3, so that if the rate of airflow falls below a predetermined level for a predetermined period of time an alarm is activated for indicating insufficient respiration by the subject.

In use, with the device 1 communicating with a subject through an appropriate mouth or nasal mask, air being inhaled and exhaled during the respective inspiratory and expiratory phases of each breathing cycle of the subject is passed through the bore 3 and the membrane 8 bends in proportion to the rate of air flow through the bore. The membrane 8 alternately bends in a generally upstream or a generally downstream direction, depending on whether the breathing cycle of the subject is at the inspiratory or expiratory phase. However, this does not affect the electronic signal outputted on the cable 16 from the membrane 8. The analogue signal on the cable 16 from the membrane 8 is converted to a digital signal in the analogue to digital converter 20 from which a corresponding digital output signal is outputted on the digital output 21 of the analogue to digital converter 20. The digital signal is then relayed to a computer for further processing. Referring now to Figs. 6 and 7, the use of the device 1 according to the invention in a respiratory monitor according to the invention indicated generally by the reference numeral 30 for monitoring breathing of a subject and also for training a subject to breathe correctly will now be described. In this embodiment of the invention the device 1 is identical to that described with reference to Figs. 1 to 5, and similar components are identified by the same reference numerals. The tubular member 2 is illustrated communicating with a subject through a communicating tube 32 which extends between the upstream end 5 of the tubular member 2 and a face mask 33 which extends over the nose and mouth of the subject. Digital signals from the analogue to digital converter 20 which represent the flow rate of air passing through the bore 3 in real time are relayed to a computing means, in this embodiment of the invention a microprocessor 34 of a computer 35. The microprocessor 34 of the computer 35 is appropriately programmed for converting the digital signals which represent the flow rate in real time into a graphical representation, which in turn is displayed on a display monitor 37. A typical graphical representation of the flow rate of air being inhaled and exhaled in real time by a subject suffering from asthma who is incorrectly breathing is illustrated by the curve A of Fig. 7. The curve A illustrates three breathing cycles of the subject. A non-volatile random access memory 38 stores in binary form a graphical representation of the flow rate of two reference breathing cycles which are ideal breathing cycles. A graphical representation of the flow rate of the two reference ideal breathing cycles are illustrated by the curve B of Fig. 7. The microprocessor 34 is programmed to simultaneously display the graphical representation B of the ideal breathing cycles along with the graphical representation A of the breathing cycles of the subject which are displayed in real time, so that the subject can compare his or her breathing cycles with ideal breathing cycles. Additionally, by virtue of the fact that the graphical representation of the breathing cycles of the subject is displayed in real time, the subject can correct his or her breathing by altering breathing so that the curve A more closely approximates to the curve B.

It is envisaged that the trace of the curve A as it is being displayed in real time will be displayed by a cursor, which may be a small dot progressively tracing the curve A. In the case of children the cursor may be an animation character, device or the like which will trace the curve A in real time.

It is also envisaged that the respective graphical representations A and B may be displayed on the monitor 37 to form a type of game, whereby the graphical representation of the reference ideal flow rate will be illustrated as a river of substantially sinusoidal shape similar to that of the curve B, and the graphical representation of the breathing cycle of the subject in real time as the breathing progresses will be illustrated by an image of a boat which would trace the curve A. The subject in order to correct his or her breathing would have to alter breathing so that the boat which would be tracing the curve A would remain within the river represented by curve B.

It is also envisaged that the device 1 as well as being suitable for monitoring respiration of a subject, may also be used for creating musical sound. For example, if the digital signals from the analogue-to-digital converter 20 were fed to a computer, such as, for example, a suitably programmed PC the signals could be converted to musical sounds and intonations. This, thus, would allow a subject to generate musical sounds and intonations, such as melodies by blowing or sucking air through the bore 3 at rates and pressures which would generate signals for in turn generating musical sounds which would be proportional to the rate of flow and/or direction of the air flowing through the bore 3.

While the device according to the invention has been described for monitoring respiration in a subject, it will of course be appreciated that the device may be used for determining other characteristics in other flowing fluids, for example, other gases or liquids.

While the membrane has been described as being provided by two laminated sheets of piezo electric film which is sold under the Registered Trade Mark KYNAR, it will be appreciated that other piezo electric film sheets may be used without departing from the scope of the invention.

It is envisaged that any suitable face mask may be provided for communicating inhaled and exhaled air by the subject through the fluid accommodating bore of the device according to the invention. In certain cases, it is envisaged that a mask may be provided which would alternately select air being inhaled through the nose of the subject and exhaled through the mouth of the subject, the nose and mouth would be selectively communicated to the fluid accommodating bore during the respective inspiratory phase and the expiratory phase, respectively of each breathing cycle. Such a mask would be particularly useful where it is desired to train a subject to inhale through his or her nose, and exhale through his or her mouth.

Claims

Claims . A device for converting a characteristic of a flowing fluid into an electronic signal indicative of the characteristic of the flowing fluid, characterised in that the device (1 ) comprises a body member (2) defining a fluid accommodating passageway (3) extending therethrough for accommodating the flowing fluid, a deformable membrane (8) extending into the passageway (3) and generally transversely thereof, the membrane (8) being deformable by the flowing fluid, the amount of deformation being proportional to the characteristic of the flowing fluid, and a sensing means (8) for detecting the amount of deformation of the membrane (8) for converting the amount of deformation of the membrane (8) into the electronic signal and for outputting the electronic signal indicative of the characteristic of the flowing fluid.

2. A device as claimed in Claim 1 characterised in that the electronic signal outputted by the sensing means (8) is proportional to the amount by which the membrane (8) is deformed.

3. A device as claimed in Claim 1 or 2 characterised in that the membrane (8) is a resilient membrane (8).

4. A device as claimed in any preceding claim characterised in that the membrane (8) is an elongated membrane (8) extending from a first end (10) to a second end (11) and being secured to the body member (2) adjacent the first end (10) thereof, the second end (11 ) being located in the passageway (3).

5. A device as claimed in Claim 4 characterised in that the second end (11) of the membrane (8) is a free end.

6. A device as claimed in Claim 3 or 4 characterised in that the membrane (8) is deformable by bending intermediate its first and second ends (10, 11).

7. A device as claimed in any of Claims 3 to 6 characterised in that the membrane (8) is deformable over its entire length in the passageway (3).

8. A device as claimed in any of Claims 4 to 7 characterised in that the fluid accommodating passageway (3) is formed by a fluid accommodating bore (3) extending through the body member (2).

9. A device as claimed in Claim 8 characterised in that the membrane (8) extends transversely across the fluid accommodating bore (3).

10. A device as claimed in Claim 8 or 9 characterised in that the membrane (8) is secured at one side of the fluid accommodating bore (3) and extends transversely across the bore (3) to the other side thereof.

11. A device as claimed in any of Claims 8 to 10 characterised in that the free end (11 ) of the membrane (8) is spaced apart from the body member (2).

12. A device as claimed in any of Claims 8 to 11 characterised in that the area of the membrane (8) presented to the flowing fluid is at least 50% of the transverse cross-sectional area of the fluid accommodating bore (3).

13. A device as claimed in any of Claims 8 to 12 characterised in that the area of the membrane (8) presented to the flowing fluid is at least 75% of the transverse cross-sectional area of the fluid accommodating bore (3).

14. A device as claimed in any of Claims 8 to 13 characterised in that the fluid accommodating bore (3) is of circular transverse cross-section.

15. A device as claimed in any of Claims 8 to 14 characterised in that the membrane (8) defines a pair of spaced apart side edges (14) extending between the respective first and second ends (10, 11 ).

16. A device as claimed in Claim 15 characterised in that the respective side edges (14) defined by the membrane (8) extending between the first and second ends (10, 11) extend parallel to each other.

17. A device as claimed in any of Claims 8 to 16 characterised in that the area of the membrane (8) presented to the flowing fluid through the fluid accommodating bore (3) is of rectangular shape.

18. A device as claimed in any preceding claim characterised in that the membrane (8) extends into the passageway (3) through a slot (12) formed in the body member (2).

19. A device as claimed in Claim 18 characterised in that the membrane (8) is sealably secured in the slot (12) in the body member (2).

20. A device as claimed in any preceding claim characterised in that the sensing means (8) comprises a piezo electric sensing means (8).

21. A device as claimed in Claim 20 characterised in that the piezo electric sensing means (8) comprises a piezo electric film (8).

22. A device as claimed in Claim 21 characterised in that the membrane (8) is formed by the piezo electric film (8).

23. A device as claimed in Claim 21 or 22 characterised in that the membrane (8) comprises a pair of piezo electric sheets laminated together to form the film (8).

24. A device as claimed in Claim 23 characterised in that the respective piezo electric sheets are of opposite polarities, and are laminated together to form the film (8).

25. A device as claimed in any of Claims 21 to 24 characterised in that the piezo electric film (8) is a film which is sold under the Trade Mark KYNAR.

26. A device as claimed in any preceding claim characterised in that the electronic signal outputted by the sensing means (8) is an analogue signal.

27. A device as claimed in Claim 26 characterised in that the device comprises an analogue to digital converter (20) for converting the analogue output signal from the sensing means (8) to a digital signal suitable for inputting to a computer (35) for further processing.

28. A device as claimed in any preceding claim characterised in that the characteristic of the flowing fluid to be converted to the electronic signal is the flow rate of flowing fluid through the passageway (3).

29. A device as claimed in any preceding claim characterised in that the device is adapted for monitoring breathing of a subject, and the characteristic being monitored is the flow rate of air being inhaled and/or exhaled by the subject during an inspiratory phase and/or an expiratory phase, respectively, of a breathing cycle.

30. A device as claimed in Claim 29 characterised in that a communicating means (32, 33) is provided for communicating the fluid accommodating passageway (3) with the subject so that air being inhaled by the subject during the inspiratory phase and/or being exhaled during the expiratory phase of a breathing cycle passes through the passageway (3).

31. A device as claimed in Claim 30 characterised in that the communicating means (32) comprises a face mask (33) adapted to communicate with the mouth of the subject.

32. A device as claimed in Claim 30 or 31 characterised in that the communicating means (32, 33) comprises a face mask (33) adapted to communicate with the nose of the subject.

33. A device as claimed in any of Claims 30 to 32 characterised in that the communicating means (32, 33) comprises a face mask (33) adapted to communicate with the mouth and the nose of the subject.

34. A device as claimed in any of Claims 30 to 33 characterised in that the communicating means (32, 33) comprises a face mask (33) adapted to alternately communicate with the nose and the mouth of the subject during inspiratory and expiratory phases, respectively, of a breathing cycle.

35. A device as claimed in any of Claims 30 to 34 characterised in that the passageway (3) communicates with atmosphere for facilitating inhaling and exhaling of air by the subject through the fluid accommodating passageway (3) of the device.

36. A monitoring device for monitoring a characteristic of a flowing fluid, the monitoring device comprising the device (1) as claimed in any preceding claim for converting a characteristic of the flowing fluid into an electronic signal indicative of the characteristic of the flowing fluid, and a reading means for reading the electronic signal outputted by the device (1).

37. A respiratory monitor for monitoring respiration of a subject, the respiratory monitor comprising a device (1 ) as claimed in any of Claims 1 to 35, and a communicating means (32, 33) communicating the fluid accommodating passageway (3) of the device (1 ) with the mouth and/or nose of the subject.

38. A respiratory monitor as claimed in Claim 37 characterised in that a storing means (38) is provided for storing a representation of a characteristic of at least one reference breathing cycle, a computing means (34) for computing the characteristic from signals received from the device (1), and a display means (37) for simultaneously displaying the computed characteristic and the reference characteristic for facilitating visual comparison of the computed characteristic with the reference characteristic.

39. A respiratory monitor as claimed in Claim 38 characterised in that the stored reference breathing cycle comprises a graphical representation of the characteristic, and the computed characteristic comprises a graphical representation of the computed characteristic.

40. A respiratory monitor as claimed in Claim 39 characterised in that the graphical representation of the reference breathing cycle comprises a graphical representation of the flow rate of inhaled and exhaled air during an inspiratory phase and an expiratory phase of the reference breathing cycle plotted against time.

41. A respiratory monitor as claimed in Claim 39 and 40 characterised in that the computed characteristic is a graphical representation of the flow rate of inhaled and exhaled air of the subject during the inspiratory phase and expiratory phase of a breathing cycle plotted against time.

42. A respiratory monitor as claimed in Claim 41 characterised in that the graphical representation of the flow rate of inhaled and exhaled air during the inspiratory and expiratory phases of a breathing cycle plotted against time is plotted against real time and is displayed in real time.

43. A respiratory monitor as claimed in any of Claims 38 to 42 characterised in that the display means comprises a visual display monitor (37).

44. A respiratory monitor as claimed in any of Claims 38 to 43 characterised in that the computing means (34) comprises a microprocessor (34).

45. A respiratory monitor as claimed in any of Claims 38 to 44 characterised in that the storing means (38) comprises a non-volatile random access memory.

46. Use of the respiratory monitor as claimed in any of Claims 37 to 45 for training a subject how to breathe by facilitating a visual comparison between a breathing cycle of the subject and a reference breathing cycle.

47. Use as claimed in Claim 46 of the respiratory monitor as claimed in any of Claims 37 to 45 characterised in that the visual comparison is facilitated by simultaneously displaying a graphical representation of the reference breathing cycle and the graphical representation of the breathing cycle of the subject.

48. Use as claimed in Claim 46 or 47 of the respiratory monitor as claimed in any of Claims 37 to 45 characterised in that the respective graphical representations of the breathing cycles are graphical representations of the flow rates of inhaled and exhaled air during the respective inspiratory and expiratory phases of a breathing cycle.

49. A method for training a subject to breathe, the method comprising the steps of monitoring a characteristic of the breathing of the subject during a breathing cycle and comparing the monitored characteristic with a corresponding characteristic of a reference ideal breathing cycle.

50. A method as claimed in Claim 49 characterised in that the method comprises graphically representing the characteristic of breathing of the subject during the breathing cycle and graphically representing the characteristic of the reference breathing cycle.

51. A method as claimed in Claim 50 characterised in that the graphical representation of the characteristic of the reference breathing cycle and the graphical representation of the characteristic of breathing of the breathing cycle of the subject are simultaneously displayed.

52. A method as claimed in Claims 50 and 51 characterised in that the graphical representation of the characteristic of breathing of the breathing cycle of the subject is displayed in real time.

53. A method as claimed in any of Claims 49 to 52 characterised in that the characteristic is the flow rate of inhaled and exhaled air during the respective inspiratory and expiratory phases of a breathing cycle.