METHOD AND APPARATUS FOR IMPROVING FLOW AND PRESSURE ESTIMATION IN CPAP SYSTEMS

• US 20170065783A1
• Filed: 11/17/2016
• Published: 03/09/2017
• Est. Priority Date: 10/21/2005
• Status: Active Grant

• Current Assignee: Resmed Limited (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Goeldi, Benriah
• Granted Patent: US 10,632,273 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61M 16/0003 Accessories therefor, e.g. sensors, vibrators, negative pressure
• 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 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/003 with a flowmeter
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2205/3334 Measuring or controlling the flow rate
• CPC Class Codes: A61M 2205/502 User interfaces, e.g. screens or keyboards

Abstract

A CPAP apparatus in which the swing in pressure at the patient interface is adjusted by regulating the air flow from the flow generator through an air delivery conduit taking into account a pressure drop representative of the inertance of the airflow in the air delivery conduit during the increase of air flow from the flow generator.

Claims

1-9. -9. (canceled)

10. A method of estimating a pressure in a patient interface of a CPAP apparatus, the method comprising:

estimating a pressure loss in an air delivery conduit of the CPAP apparatus based on a sensed flow through the air delivery conduit and a derivative of the sensed flow through the air delivery conduit;

estimating the pressure in the patient interface by subtracting the estimated pressure loss in the air delivery conduit from a sensed pressure at a flow generator of the CPAP apparatus.

11. The method of claim 10, wherein the pressure loss (P_drop) in the air delivery conduit is estimated as

P_drop=K₁Q²+K₂Q+K_LdQ/dt;

where Q is the flow through the air delivery conduit, K₁ and K2 are empirically determined constants, K_L, is an analytically determined flow inertance, and dQ/dt is the derivative of the flow through the air delivery conduit.

12. The method of claim 11, wherein the flow inertance K_L is analytically determined as

K_L=ρ

I/A

where ρ

is the density of the air in the air delivery conduit, I is the length of the air delivery conduit, and A is the cross sectional area of the air delivery conduit.

13. The method of claim 10, further comprising converting the derivative of the flow through the air delivery conduit to a converted value before estimating the pressure loss.

14. The method of claim 13, wherein converting the derivative comprises setting the derivative to zero for negative values of the derivative.

15. The method of claim 13, wherein converting the derivative comprises clamping the derivative at a maximum positive value of the derivative.

16. The method of claim 15, wherein the maximum positive value is 2.5 L/s/s.

17. The method of claim 10, further comprising controlling the flow generator by maintaining the estimated pressure in the patient interface to be substantially equal to a desired pressure.

18. A CPAP apparatus comprising:

a flow generator,

a patient interface,

an air delivery conduit for delivering air from the flow generator to the patient interface,

a pressure sensor for sensing a pressure at the flow generator,

a flow sensor for sensing a flow through the air delivery conduit, and

a control mechanism configured to estimate the pressure in the patient interface by

estimating a pressure loss in the air delivery conduit based on the sensed flow and a derivative of the sensed flow;

subtracting the estimated pressure loss in the air delivery conduit from the sensed pressure at the flow generator.

19. The CPAP apparatus of claim 18, wherein the control mechanism is further configured to control the flow generator to maintain the estimated pressure in the patient interface to be substantially equal to a desired pressure.