DETERMINATION OF LEAK DURING CPAP TREATMENT

• US 20100101574A1
• Filed: 08/30/2007
• Published: 04/29/2010
• Est. Priority Date: 08/30/2006
• Status: Active Grant

• Current Assignee: ResMed Pty Ltd. (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Bassin, David John
• Granted Patent: US 8,256,418 B2
• Time in Patent Office: Days
• US Class Current: 128/204.210
• CPC Class Codes: A61M 16/0057 Pumps therefor
• 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 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase
• CPC Class Codes: A61M 2205/15 Detection of leaks
• CPC Class Codes: A61M 2205/16 with back-up system in case of failure
• CPC Class Codes: A61M 2205/50 with microprocessors or computers

Abstract

In a CPAP or positive pressure ventilation system, leak is determined at each instant by a lookback for a time as long as single breath to establish the start of an averaging window over which low-pass filtered values used in the determination of a parameter of a leak model are averaged. A jamming index indicates whether the leak is rapidly changing. To the extent that jamming is high, the leak estimate used progressively changes from that using sliding breath-window averaging to a more robust and faster responding low-pass filter method, and adjustment of ventilatory support based on measures employing estimated respiratory flow is slowed down or stopped.

Claims

1. A method of determining a mask leak conductance in a patient respiratory device, comprising the steps of

determining a first estimate of leak conductance which responds relatively quickly to changes in leak conductance,

determining a second estimate of leak conductance which responds more slowly to changes in leak conductance, and

determining the mask leak conductance as a function of the first and second estimates of leak conductance.

2. A method according to claim 1, further comprising the step of determining the pressure in the mask.

3. A method according to claim 2, further comprising determining an estimate of non-deliberate mask leak as a function of the mask leak conductance and the mask pressure.

4. A method according to claim 3, wherein the non-deliberate mask leak is calculated as:

Q_leak=G_J√

{square root over (P_mask)}.

wherein;

Q_leak is non-deliberate mask leak,

G_j is mask leak conductance, and

P_mask is mask pressure.

5. A method according to claim 1, further comprising the step of determining an uncompensated leak index representative of an extent to which mask leak is uncompensated.

6. A method according to claim 5, wherein the mask leak conductance is calculated as a function of the uncompensated leak index and the first and second estimates of leak conductance.

7. A method according to claim 6, wherein the mask leak conductance is calculated as:

G_j=JG₁+(1−

J)G₂

wherein;

G_j is the estimate of mask leak conductance,

G₁ is the first estimate of leak conductance,

G₂ is the second estimate of leak conductance, and

J is an jamming index of uncompensated mask leak.

8. A method of claim 7, wherein the jamming index is between zero and one.

10. A method according to claim 8, wherein the level of ventilatory support is adjusted at a rate which is a function of said index.

9. A method of providing ventilatory support to a patient, comprising the steps of:

determining a jamming index indicative of an extent to which non-deliberate leak is uncompensated;

adjusting a level of ventilatory support in accordance with said jamming index.

11. A method according to claim 9, wherein said rate of adjustment is decreased with increasing uncompensated non-deliberate leak.

12. A system of providing ventilatory support to a patient, comprising the steps of:

determining a jamming index indicative of an extent to which non-deliberate leak is uncompensated;

adjusting a level of ventilatory support in accordance with said jamming index.