Determination of leak and respiratory airflow

• US 6,659,101 B2
• Filed: 07/10/2001
• Issued: 12/09/2003
• Est. Priority Date: 08/14/1996
• Status: Expired due to Term

• Current Assignee: Resmed Limited (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Berthon-Jones, Michael
• Primary Examiner(s): Lewis, Aaron J.
• Assistant Examiner(s): MITCHELL, TEENA KAY
• Application Number:
  US09/902,011
• Publication Number:
  US 20020069874A1
• Time in Patent Office: 882 Days
• Field of Search: 128/200.24, 128/204.18, 128/204.21, 128/202.22, 128/204.23, 128/204.26, 128/207.14, 128/207.18, 600/484, 600/529, 600/533, 600/538
• US Class Current: 128/204.21
• CPC Class Codes: A61M 16/0003 Accessories therefor, e.g. sensors, vibrators, negative pressure
• CPC Class Codes: A61M 16/0057 Pumps therefor
• 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 2016/0021 with a proportional output signal, e.g. from a thermistor
• CPC Class Codes: A61M 2016/0027 pressure meter
• CPC Class Codes: A61M 2016/0033 electrical
• 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

Abstract

Methods and apparatus for determining leak and respiratory airflow are disclosed. A pressure sensor (34) and a differential pressure sensor (32) have connection with a pneumotach (24) to derive instantaneous mask pressure and airflow respectively. A microcontroller (38) estimates a non-linear conductance of any leak path occurring at a mask (12) as being the low pass filtered instantaneous airflow divided by the low pass filtered square root of the instantaneous pressure. The instantaneous leak flow is then the conductance multipled by the square root of the instantaneous pressure, and the respiratory airflow is calculated as being the instantaneous airflow minus the instantaneous leak flow. The time constants for the low pass filtering performed by the microcontroller (38) can be dynamically adjusted dependent upon sudden changes in the instantaneous leak flow.

Claims

1. In an apparatus with circuitry for airway treatment for a patient, a method for determining a degree of certainty that a leak has suddenly increased during airway treatment comprising the steps of:

determining a measure of respiratory airflow to the patient;

determining an extent A to which the measure has been positive for longer than expected;

determining an extent B to which the measure is large and positive;

determining the degree of certainty that a leak has suddenly increased as a function of extent A and extent B.

2. The method of claim 1 wherein said extent A is a fuzzy index.

3. The method of claim 1 wherein said extent B is a fuzzy index.

4. The method of claim 1 wherein said function of extent A and extent B is a fuzzy intersection of extent A and extent B.

5. In an apparatus with control circuitry for airway treatment for a patient, a method for determining a degree of certainty that a leak has suddenly decreased during airway treatment comprising the steps of:

determining a measure of respiratory airflow to the patient;

determining an extent A to which the measure has been negative for longer than expected;

determining an extent B to which the measure is large and negative;

determining the degree of certainty that a leak has suddenly decreased as a function of extent A and extent B.

6. The method of claim 5 wherein said extent A is a fuzzy index.

7. The method of claim 5 wherein said extent B is a fuzzy index.

8. The method of claim 5 wherein said function of extent A and extent B is a fuzzy intersection of extent A and extent B.

9. In an apparatus with control circuitry for airway treatment for a patient, a method for determining an extent to which a leak has suddenly changed during airway treatment of a patient comprising the steps of:

determining an increase-index of a degree of certainty to which the leak has suddenly increased;

determining a decrease-index of a degree of certainty to which the leak has suddenly decreased; and

determining the extent to which the leak has suddenly changed as a function of the increase-index and the decrease-index.

10. The method of claim 9 wherein said increase-index is calculated as a function of a measure of respiratory airflow.

11. The method of claim 10 wherein said function of a measure of respiratory airflow is a fuzzy membership function.

12. The method of claim 11 wherein said function of the increase-index and the decrease-index is a fuzzy union of the increase-index and the decrease-index.

13. The method of claim 9 wherein said decrease-index is calculated as a function of a measure of respiratory airflow.

14. The method of claim 13 wherein said function of a measure of respiratory airflow is a fuzzy membership function.

15. The method of claim 14 wherein said function of the increase-index and the decrease-index is a fuzzy union of the increase-index and the decrease-index.

16. An apparatus for determining a degree of certainty that a leak has suddenly increased during airway treatment of a patient comprising:

means for delivering a controlled supply of pressure support to a patient'"'"'s airway;

means for determining a flow signal representative of respiratory airflow to the patient;

a control means in communication with the means for determining, the control means having programmed instructions for controlling a determination of a degree of certainty that a leak has suddenly increased, the instructions controlling steps comprising;

determining a measure of respiratory airflow to the patient from the flow signal;

determining an extent A to which the measure has been positive for longer than expected;

determining an extent B to which the measure is large and positive;

determining the degree of certainty that a leak has suddenly increased as a function of extent A and extent B.

17. The apparatus of claim 16 wherein said extent A is a fuzzy index.

18. The apparatus of claim 16 wherein said extent B is a fuzzy index.

19. The apparatus of claim 16 wherein said function of extent A and extent B is a fuzzy intersection of extent A and extent B.

20. An apparatus for determining a degree of certainty that a leak has suddenly increased during airway treatment of a patient comprising:

means for delivering a controlled supply of pressure support to a patient'"'"'s airway;

means for determining a flow signal representative of respiratory airflow to the patient;

a control means in communication with the means for determining, the control means having programmed instructions for controlling a determination of a degree of certainty that a leak has suddenly decreased, the instructions controlling steps of;

determining a measure of respiratory airflow to the patient from the flow signal;

determining an extent A to which the measure has been negative for longer than expected;

determining an extent B to which the measure is large and negative;

determining the degree of certainty that a leak has suddenly decreased as a function of extent A and extent B.

21. The apparatus of claim 20 wherein said extent A is a fuzzy index.

22. The apparatus of claim 20 wherein said extent B is a fuzzy index.

23. The apparatus of claim 20 wherein said function of extent A and extent B is a fuzzy intersection of extent A and extent B.

24. An apparatus with coded control circuitry for airway treatment for a patient for determining an extent to which a leak has suddenly changed during airway treatment of a patient comprising:

means for delivering a controlled supply of pressure support to a patient'"'"'s airway;

means for determining a flow signal representative of respiratory airflow to the patient;

a control means in communication with the means for determining, the control means having coded instructions for controlling a determination of a degree of certainty that a leak has suddenly changed, the instructions controlling steps comprising;

determining an increase-index of a degree of certainty to which the leak has suddenly increased;

determining a decrease-index of a degree of certainty to which the leak has suddenly decreased; and

determining the extent to which the leak has suddenly changed as a function of the increase-index and the decrease-index.

25. The apparatus of claim 24 wherein said increase-index is calculated as a function of a measure of respiratory airflow.

26. The apparatus claim 25 wherein said function of a measure of respiratory airflow is a fuzzy membership function.

27. The apparatus of claim 26 wherein said function of the increase-index and the decrease-index is a fuzzy union of the increase-index and the decrease-index.

28. The apparatus of claim 24 wherein said decrease-index is calculated as a function of a measure of respiratory airflow.

29. The apparatus of claim 28 wherein said function of a measure of respiratory airflow is a fuzzy membership function.

30. The apparatus of claim 29 wherein said function of the increase-index and the decrease-index is a fuzzy union of the increase-index and the decrease-index.