Characterisation of mask systems

• US 20040074495A1
• Filed: 11/06/2003
• Published: 04/22/2004
• Est. Priority Date: 12/29/2000
• Status: Active Grant

• Current Assignee: ResMed Pty Ltd. (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Wickham, Peter John Deacon, Wickham, Nicola Frances
• Granted Patent: US 7,987,847 B2
• Time in Patent Office: Days
• US Class Current: 128/204.18
• CPC Class Codes: A61M 16/00 Devices for influencing the respiratory system of patients by gas treatment, e.g. mouth-to-mouth respiration; Tracheal tubes stimulating the respiratory movement by mechanical, pneumatic or electrical means, iron lungs combined with gas breathing means A61H31/00
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/0066 Blowers or centrifugal pumps
• CPC Class Codes: A61M 16/0069 the speed thereof being controlled by respiratory parameters, e.g. by inhalation
• CPC Class Codes: A61M 16/024 including calculation means, e.g. using a processor
• CPC Class Codes: A61M 16/06 Respiratory or anaesthetic masks
• CPC Class Codes: A61M 16/0858 Pressure sampling ports
• CPC Class Codes: A61M 16/1055 bacterial
• CPC Class Codes: A61M 16/106 in a path
• CPC Class Codes: A61M 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2205/15 Detection of leaks
• CPC Class Codes: A61M 2205/3331 Pressure; Flow
• CPC Class Codes: A61M 2205/505 Touch-screens; Virtual keyboard or keypads; Virtual buttons; Soft keys; Mouse touches
• CPC Class Codes: A61M 2205/70 with testing or calibration facilities
• CPC Class Codes: A61M 2230/46 Resistance or compliance of the lungs

Abstract

A method and a CPAP apparatus (10) for characterizing a plurality of different mask systems (14), e.g., masks and hoses, are provided. The CPAP apparatus (10) can be calibrated for different mask systems (14) and hoses (16) by including sensors (13,15) configured to measure flow and pressure at a flow generator (12) of the CPAP apparatus (10). When the flow generator (12) is fitted to a new mask system (14), or any changes are made to an existing mask system (14), mask or patient interface (34) and/or hose (16), a method of calibrating the flow generator (12) for the new mask system (14), mask (34) and/or hose (16) is provided. The method includes determining air flow characteristics of the hose (16) using flow measurements made during a first test period when the flow through the mask system (14) is open, measuring or estimating pressure in the mask system (14) during a second test period when the flow through the mask system (14) is blocked and determining air flow characteristics of the diffuser (36) of the mask system (14) using the air flow characteristics of the air delivery hose (16) determined during the first test period and the pressure measurements made during the second test period.

Claims

1. A method of determining air flow characteristics of a mask system connected to CPAP apparatus comprising a flow generator, the mask system including an air delivery hose and a patient interface including a diffuser, the flow generator including a controllable air blower, a flow sensor and a pressure sensor, the method comprising:

determining air flow characteristics of the air delivery hose using flow measurements made during a first test period when the flow through the patient interface is open;

measuring pressure in the patient interface during a second test period when the flow through the patient interface is blocked; and

determining air flow characteristics of the diffuser using the air flow characteristics of the air delivery hose determined during the first test period and the pressure measurements made during the second test period.

2. A method according to claim 1, further comprising processing the air flow characteristics of the air delivery hose and the air flow characteristics of the diffuser.

3. A method according to any one of claims 1 or 2, wherein the determining of the air flow characteristics of the air delivery hose is calculated as a function of a quadratic expression with two hose constants.

4. A method according to claim 3, wherein the two hose constants comprise:

HoseA=(yX²−

xY²)and HoseB=(xY−

yX)/(xX²−

x²X),

wherein x is a lower air flow for the air delivery hose, X is an upper air flow for the air delivery hose, y is a pressure drop in the air delivery hose at the lower air flow and Y is a pressure drop in the air delivery hose at the upper air flow.

5. A method according to claim 4, wherein the two hose constants (Hose A, Hose B) are used to calculate a true lower test pressure (TrueDiffTP1) and a true upper test pressure (TrueDiffTP2) for the diffuser,

wherein the true lower test pressure is defined as TrueDiffTP1=DiffTP 1−

HoseA*x−

HoseB*HoseA(x)², where DiffTP1 is the diffuser flow at a lower pressure for the diffuser, and

wherein the true higher test pressure is defined as TrueDiffTP2=DiffTP2−

HoseA*X−

HoseB*HoseA(X)², where DiffTP2 is the diffuser flow at a higher pressure for the diffuser.

6. A method according to any one of claims 1-5, wherein the determining of the air flow characteristics of the mask system is calculated as a function of a quadratic expression with two diffuser constants (Diff A, Diff B).

7. A method according to claim 6, wherein the two diffuser constants comprise:

DiffA=(zV²−

vZ²)/(vV²−

Vv₂) and DiffB=(vZ−

zV)/(vV²−

v²−

Vv²),

wherein v is a lower pressure for the diffuser, V is an upper pressure for the diffuser, z is a true lower pressure for the diffuser and Z is a true upper pressure for the diffuser.

8. A method according to any one of claims 1-7, further comprising blocking the patient interface with a flow blocking member having a shape that is complementary to a shape of the patient interface.

9. A method according to claim 8, wherein the shape of the flow blocking member is representative of at least one of a human nose and a human face.

10. A method according to any one of claims 8-9, further comprising affixing the flow blocking member to the patient interface.

30. A machine readable medium containing machine executable instructions for carrying out the method according to any one of claims 1-16.

38. A CPAP apparatus for performing the method according to any one of claims 1-16 and 34-37.

11. A method of determining air flow characteristics of an air delivery hose connected to a flow generator in a CPAP apparatus, the flow generator including a controllable air blower, a flow sensor and a pressure sensor, the method comprising:

measuring an air flow rate through the controllable air blower during a test period; and

determining air flow characteristics of the air delivery hose using the flow rate measurements made during the test period.

12. A method of determining air flow characteristics of a mask system connected to a controllable source of breathable gas, the mask system including an air delivery hose and a patient interface, the method comprising:

measuring an air flow rate at the controllable source of breathable gas during a controlled pressure test period when the mask system is open;

measuring a pressure at the controllable source of breathable gas during a controlled flow test period when the mask system is blocked; and

determining air flow characteristics of the mask system based on the measured pressure and the measured air flow rate made during the controlled pressure test period and the controlled flow test period, respectively.

13. A method in accordance with claim 12, further comprising controlling the source of breathable gas to deliver air at a first substantially constant pressure and subsequently at a second substantially constant pressure during the controlled pressure test period.

14. A method in accordance with claim 13, wherein the first substantially constant pressure is lower than the second substantially constant pressure.

15. A method in accordance with any one of claims 12-14, further comprising controlling the source of breathable gas to deliver air at a first substantially constant flow rate and subsequently at a second substantially constant flow rate during the controlled flow test period.

16. A method in accordance with claim 15, wherein the first substantially constant flow rate is lower than the second substantially constant flow rate.

17. A CPAP apparatus useful in treatment of a patient, the CPAP apparatus comprising:

a housing;

a respiratory mask system in communication with the housing, the respiratory mask system comprising an air delivery hose and a patient interface including a diffuser;

a flow generator configured to deliver a supply of breathable gas to the patient and being associated with the housing, the flow generator being controllable to supply a controllable source of breathable gas to the patient interface through the air delivery hose during a test period, wherein a plurality of flow measurements of the controllable source of breathable gas are made during the test period; and

a processor configured to determine a plurality of air flow characteristics of the respiratory mask system at least based on the plurality of flow measurements made during the test period.

18. A CPAP apparatus according to claim 17, wherein the flow sensor is configured to measure at least one air flow through the patient interface during the test period when the flow through the patient interface is open.

19. A CPAP apparatus according to any one of claims 17 and 18, wherein the pressure sensor is configured to measure at least one pressure in the patient interface during the test period when the flow through the patient interface is blocked.

20. A CPAP apparatus according to any one of claims 17-19, wherein the processor is configured to determine air flow characteristics of the diffuser using the air flow characteristics of the air delivery hose determined during a first portion of the test period and the pressure measurements made during a second portion of the test period.

21. A CPAP apparatus according to any one of claims 17-20, wherein the processor is configured to calculate the air flow characteristics of the air delivery hose as a function of a quadratic expression with two hose constants.

22. A CPAP apparatus according to claim 21, wherein the two hose constants comprise:

HoseA=(yX²−

xY²/(xX²−

Xx²) and HoseB=(xY−

yX)/(xX²−

X²X),

wherein x is a lower air flow for the air delivery hose, X is an upper air flow for the air delivery hose, y is a pressure drop in the air delivery hose at the lower air flow and Y is a pressure drop in the air delivery hose at the upper air flow.

23. A CPAP apparatus according to claim 22, wherein the two hose constants (Hose A, Hose B) are used to calculate a true lower test pressure (TrueDiffTP1) and a true upper test pressure (TrueDiffTP2) for the diffuser,

wherein the true lower test pressure is defined as TrueDiffTP 2=DiffTP1−

HoseA*x−

HoseB*HoseA(x)², where DiffTP1 is the diffuser flow at a lower pressure for the diffuser, and

wherein the true higher test pressure is defined as TrueDiffTP2=DiffTP2−

HoseA*X−

HoseB*HoseA(X)², where DiffTP2 is the diffuser flow at a higher pressure for the diffuser.

24. A CPAP apparatus according to any one of claims 17-23, wherein the determining of the air flow characteristics of the mask system is calculated as a function of a quadratic expression with two diffuser constants (Diff A, Diff B).

25. A CPAP apparatus according to claim 24, wherein the two diffuser constants comprise:

DiffA=(zV²−

vZ²)/(vV²−

Vv²) and DiffB=(vZ−

zV)/(vV²−

v²V),

wherein v is a lower pressure for the diffuser, V is an upper pressure for the diffuser, z is a true lower pressure for the diffuser and Z is a true upper pressure for the diffuser.

26. A CPAP apparatus according to any one of claims 17-25, further comprising a flow blocking member configured to block the patient interface, the flow blocking member (50) having a shape that is complementary to a shape of the patient interface.

27. A CPAP apparatus according to claim 26, wherein the shape of the flow blocking member is representative of at least one of a human nose and a human face.

28. A CPAP apparatus according to claim 26 or 27, wherein the flow blocking member is affixed to the patient interface.

29. A CPAP apparatus according to any one of claims 17-28, wherein the patient interface is configured to allow air to pass therethrough and the diffuser is configured to diffuse exhaled air therethrough during an exhalation phase of a respiratory cycle of the patient.

31. A CPAP apparatus useful in treatment of a patient, the CPAP apparatus comprising:

a housing;

a respiratory mask system in communication with the housing, the respiratory mask system comprising an air delivery hose and a patient interface including a diffuser orifice;

a flow generator configured to deliver a supply of breathable gas to the patient and being associated with the housing, the flow generator being controllable to supply a controllable source of breathable gas to the patient interface through the air delivery hose during a test period, wherein a plurality of flow measurements of the controllable source of breathable gas are made during the test period;

means for determining air flow characteristics of the air delivery hose using flow measurements made during a first portion of the test period when the flow through the patient interface is open;

means for measuring pressure in the patient interface during a second portion of the test period when the flow through the patient interface is blocked; and

means for determining air flow characteristics of the orifice using the air flow characteristics of the air delivery hose determined during the first portion of the test period and the pressure measurements made during a second portion of the test period.

32. A CPAP apparatus for use with a respiratory mask system comprising an air delivery hose and a patient interface including a diffuser, the CPAP apparatus comprising:

a housing;

a flow generator configured to deliver a supply of breathable gas to the patient and being associated with the housing, the flow generator being controllable to supply a controllable source of breathable gas to the patient interface through the air delivery hose during a test period, wherein a plurality of flow measurements of the controllable source of breathable gas are made during the test period; and

a processor configured to determine a plurality of air flow characteristics of the respiratory mask system at least based on the plurality of flow measurements made during the test period.

33. A respiratory mask system for use with a CPAP apparatus of claim 32.

34. A method of calibrating a flow generator in a CPAP apparatus for use with a mask system including a diffuser and an air delivery hose connecting the flow generator and the mask system, the method comprising:

providing the flow generator with two different air flows, representative of a pressure drop in the air delivery hose when flow through the mask system is open;

providing the mask system with two different pressures, representative of a flow of the diffuser and other leaks out of the mask system;

blocking flow through the mask system while providing the mask system with the two different pressures.

35. A method of determining air flow characteristics of a mask system connected to CPAP apparatus comprising a flow generator, the mask system including an air delivery hose and a patient interface including a diffuser, the CPAP apparatus including a controllable air blower, a flow sensor and a pressure sensor, the method comprising:

providing air flow characteristics of the air delivery hose;

measuring pressure in the patient interface when the flow through the patient interface is blocked; and

determining air flow characteristics of the diffuser using the pressure measurements when the patient interface is blocked and the air flow characteristics of the air delivery hose that are provided or determined.

36. A method according to claim 35, wherein the air flow characteristics of the air delivery hose are predetermined.

37. A method according to claim 35, wherein the air flow characteristics of the air delivery hose are measured when flow through the patient interface is open.