Administration of CPAP treatment pressure in presence of apnea

• US 6,502,572 B1
• Filed: 03/21/2000
• Issued: 01/07/2003
• Est. Priority Date: 11/07/1997
• Status: Expired due to Term

• Current Assignee: Resmed Limited (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Berthon-Jones, Michael, Farrugia, Steven Paul
• Primary Examiner(s): Lewis, Aaron J.
• Assistant Examiner(s): Patel, Mital
• Application Number:
  US09/531,915
• Time in Patent Office: 1,022 Days
• Field of Search: 128/204.18, 128/204.21, 128/204.23
• US Class Current: 128/204.23
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/4818 Sleep apnoea
• CPC Class Codes: A61B 5/4836 Diagnosis combined with treatment in closed-loop systems or methods A61B5/0036 takes precedence
• 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 16/0003 Accessories therefor, e.g. sensors, vibrators, negative pressure
• CPC Class Codes: A61M 16/0051 with alarm devices
• 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 16/0875 Connecting tubes
• CPC Class Codes: A61M 2016/0036 in the breathing tube and used in both inspiratory and expiratory phase

Abstract

CPAP treatment apparatus is disclosed having a controllable flow generator (34, 38, 40) operable to produce breathable gas at a treatment pressure elevated above atmosphere to a patient by a delivery tube (32) coupled to a mask (30) having connection with a patient'"'"'s airway. A sensor (44, 50, 56, 58) generates a signal representative of patient respiratory flow, that is provided to a controller (54, 62, 64). The controller (54, 62, 64) is operable to determine the occurrence of an apnea from a reduction in respiratory airflow below a threshold, and if an apnea has occurred, to determine the duration of the apnea and to cause the flow generator (34, 38) to increase the treatment pressure. In one preferred form the increase in pressure is zero if the treatment pressure before the apnea exceeds a pressure threshold. Below the pressure threshold the increase in pressure is an increasing function of the duration of the apnea multiplied by the difference between the pressure threshold and the current treatment pressure.

Claims

1. A method for the administration of CPAP therapy comprising the steps of:

supplying breathable gas to a patient'"'"'s airway at a treatment pressure;

determining a measure of respiratory airflow;

determining an occurrence of apnea from a reduction in the measure of respiratory airflow and, in response to the occurrence of apnea, (i) determining a duration of the occurrence of apnea; and

(ii) increasing the treatment pressure by an amount which is an increasing function of the duration of the apnea,

wherein said increasing function is zero for zero apnea duration, and exponentially approaches an upper limit as apnea duration increases indefinitely.

2. The method of claim 1 wherein said amount of increase is also a decreasing function of the treatment pressure immediately before the occurrence of apnea.

3. The method of claim 2 wherein said decreasing function is a difference between a pressure threshold and a current treatment pressure.

4. The method of claim 3 further comprising the step of decreasing the treatment pressure following a time interval during which there was no apnea.

5. The method of claim 4 wherein the amount of increase in treatment pressure is zero if the treatment pressure before the occurrence of apnea exceeded a pressure threshold.

6. The method of claim 5 wherein the pressure threshold is 10 cmH₂O.

7. The method of claim 6 wherein during a continued absence of apneas the treatment pressure is gradually reduced towards an initial treatment pressure.

8. The method of claim 7 wherein the occurrence of an apnea is determined by the steps of:

calculating RMS respiratory airflow over a short time interval;

calculating RMS respiratory airflow over a longer time interval; and

determining onset of an apnea if the RMS respiratory airflow over said short time interval is less than a predetermined fraction of the RMS respiratory airflow over said longer time interval.

9. The method of claim 1 further comprising a step of determining whether the patient'"'"'s airway is patent during an occurrence of apnea and, if the airway is patent, not increasing the treatment pressure.

10. CPAP treatment apparatus comprising:

a controllable flow generator operable to provide breathable gas at a pressure elevated above atmospheric;

a gas delivery tube coupled to said flow generator;

a patient mask coupled to said gas delivery tube to receive breathable gas from said flow generator and to provide said gas, at a desired treatment pressure, to a patient'"'"'s airway;

a processor operable to receive input and to control a magnitude of the treatment pressure provided by said flow generator; and

a pressure transducer to sense patient respiratory airflow and to generate input for said processor;

said processor programmed to perform the steps of;

determining a treatment pressure;

determining a measure of respiratory airflow;

determining an occurrence of apnea from a reduction in the measure of respiratory airflow and, in response to the occurrence of apnea, (i) determining a duration of the occurrence of apnea; and

(ii) increasing the treatment pressure by an amount which is an increasing function of the duration of the apnea,

wherein said increasing function is zero for zero apnea duration, and exponentially approaches an upper limit as apnea duration increases indefinitely.

11. The apparatus of claim 10 wherein the amount of increase is also a decreasing function of the treatment pressure immediately before the occurrence of apnea.

12. The apparatus of claim 11 wherein said decreasing function is a difference between a pressure threshold and a current treatment pressure.

13. The apparatus of claim 12 wherein said processor is further programmed to perform the step of decreasing the treatment pressure following a time interval during which there was no apnea.

14. The apparatus of claim 13 wherein the amount of increase in treatment pressure is zero if the treatment pressure before the occurrence of apnea exceeded a pressure threshold.

15. The apparatus of claim 14 wherein the pressure threshold is 10 cmH₂O.

16. The apparatus of claim 15 wherein said processor is further programmed to gradually reduce the treatment pressure towards an initial treatment pressure during a continued absence of apneas.

17. The apparatus of claim 16 wherein the occurrence of an apnea is determined by the steps of:

calculating RMS respiratory airflow over a short time interval;

calculating RMS respiratory airflow over a longer time interval; and

determining onset of an apnea if the RMS respiratory airflow over said short time interval is less than a predetermined fraction of the RMS respiratory airflow over said longer time interval.

18. The apparatus of claim 10 wherein said processor is further programmed to perform a step of determining whether the patient'"'"'s airway is patent during an occurrence of apnea and, if the airway is patent, not increasing the treatment pressure.

19. CPAP treatment apparatus comprising:

a flow means to provide breathable gas at a treatment pressure elevated above atmospheric to a patient'"'"'s airway;

a controller means to receive an input signal and to control a magnitude of the treatment pressure provided by said flow generator; and

sensor means to detect patient respiratory airflow and to generate an input signal to said controller;

said controller means programmed to perform the steps of;

determining a treatment pressure;

determining a measure of respiratory airflow;

determining an occurrence of apnea from a reduction in the measure of respiratory airflow and, in response to the occurrence of apnea, (i) determining a duration of the occurrence of apnea; and

(ii) increasing the treatment pressure by an amount which is an increasing function of the duration of the apnea,

wherein said increasing function is zero for zero apnea duration, and exponentially approaches an upper limit as apnea duration increases indefinitely.

20. The apparatus of claim 19 wherein the amount of increase is also a decreasing function of the treatment pressure immediately before the occurrence of apnea.

21. The apparatus of claim 20 wherein said decreasing function is a difference between a pressure threshold and a current treatment pressure.

22. The apparatus of claim 21 wherein said control means is further programmed to perform the step of decreasing the treatment pressure following a time interval during which there was no apnea.

23. The apparatus of claim 22 wherein the amount of increase in treatment pressure is zero if the treatment pressure before the occurrence of apnea exceeded a pressure threshold.

24. The apparatus of claim 23 wherein the pressure threshold is 10 cmH₂O.

25. The apparatus of claim 24 wherein said controller means is further programmed to gradually reduce the treatment pressure towards an initial treatment pressure during a continued absence of apneas.

26. The apparatus of claim 25 wherein the occurrence of an apnea is determined by the steps of:

calculating RMS respiratory airflow over a short time interval;

calculating RMS respiratory airflow over a longer time interval; and

determining onset of an apnea if the RMS respiratory airflow over said short time interval is less than a predetermined fraction of the RMS respiratory airflow over said longer time interval.

27. The apparatus of claim 19 wherein said controller is further programmed to perform a step of determining whether the patient'"'"'s airway is patent during an occurrence of apnea and, if the airway is patent, not increasing the treatment pressure.