Methods and devices for the detection of hypopnoea

• US 9,364,180 B2
• Filed: 02/11/2015
• Issued: 06/14/2016
• Est. Priority Date: 06/05/2009
• Status: Active Grant

• Current Assignee: ResMed Pty Ltd. (ResMed Incorporated)
• Original Assignee: Resmed Limited (ResMed Incorporated)
• Inventors: Armitstead, Jeffrey Peter
• Primary Examiner(s): WOODWARD, VALERIE LYNN
• Application Number:
  US14/619,499
• Publication Number:
  US 20150150500A1
• Time in Patent Office: 489 Days
• US Class Current: 1/1
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/4818 Sleep apnoea
• CPC Class Codes: A61B 5/725 using specific filters therefor, e.g. Kalman or adaptive filters A61B5/316 take precedence
• CPC Class Codes: A61B 5/7278 Artificial waveform generation or derivation, e.g. synthesising signals from measured signals A61B5/327 takes precedence
• CPC Class Codes: A61B 5/7282 Event detection, e.g. detecting unique waveforms indicative of a medical condition A61B5/4094, A61B5/4818, A61B5/349, A61B5/0823 take precedence
• CPC Class Codes: A61M 16/0003 Accessories therefor, e.g. sensors, vibrators, negative pressure
• 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 16/0666 Nasal cannulas or tubing devices for improving normal breathing through the nose A61F5/08; nose filters A62B23/06; outside holding devices A61M25/02
• CPC Class Codes: A61M 16/0875 Connecting tubes
• CPC Class Codes: A61M 2016/003 with a flowmeter
• CPC Class Codes: A61M 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2205/3334 Measuring or controlling the flow rate
• CPC Class Codes: A61M 2205/505 Touch-screens; Virtual keyboard or keypads; Virtual buttons; Soft keys; Mouse touches
• CPC Class Codes: A61M 2230/005 Parameter used as control input for the apparatus
• CPC Class Codes: A61M 2230/205 partial oxygen pressure (P-O2)
• CPC Class Codes: A61M 2230/40 Respiratory characteristics

Abstract

Automated methods provide hypopnea detection for determining a hypopnea event and/or a severity of a hypopnea event. In some embodiments, a calculated short-term variance of a measured respiratory flow signal are compared to first and second proportions of a calculated long-term variance of the measured flow signal. A detection of the hypopnea may be indicated if the first measure falls below and does not exceed a range of the first and second proportions during a first time period. In some embodiments, a hypopnea severity measure is determined by automated measuring of an area bounded by first and second crossings of a short-term measure of ventilation and a proportion of a long-term measure. The detection methodologies may be implemented for data analysis by a specific purpose computer, a detection device that measures a respiratory airflow or a respiratory treatment apparatus that provides a respiratory treatment regime based on the detected hypopneas.

Claims

1. An apparatus to detect a hypopnea from a measured flow of breathable gas, the apparatus comprising:

a controller having at least one processor to access data representing a measured flow of breathable gas, the controller being further configured to;

determine a long-term measure of ventilation from the measured flow;

determine a short-term measure of ventilation from the measured flow;

determine a threshold as a proportion of the long-term measure of ventilation;

measure an area bounded by first and second crossings of the short-term measure of ventilation and the threshold; and

detect the hypopnea with the measured area.

2. The apparatus of claim 1 wherein the controller is configured to measure the area by integrating a difference between the threshold and the short-term measure of ventilation during a time period from when the short-term measure falls below the threshold to when the short-term measure exceeds the threshold.

3. The apparatus of claim 1 wherein the controller is configured to measure the area by adding a plurality of sample differences during a time period from when the short-term measure falls below the threshold to when the short-term measure exceeds the threshold, wherein each sample difference is a difference between a sample of the threshold and a sample of the short-term measure of ventilation.

4. The apparatus of claim 1 wherein the controller is further configured to impede a further detection of a hypopnea during a refractory period initiated by detection of the second crossing.

5. The apparatus of claim 1 wherein the controller is further configured to trigger the measuring of the area upon detecting the first crossing by comparing the short-term measure of ventilation and the threshold for inequality.

6. The apparatus of claim 5 wherein the detection of the hypopnea is contingent upon a time from the first crossing to the second crossing exceeding about ten seconds.

7. The apparatus of claim 1 wherein the short-term measure of ventilation comprises an output of low pass filtering half of an absolute value of a measure of flow of breathable gas with a first time constant.

8. The apparatus of claim 7 wherein the long-term measure of ventilation comprises an output of low pass filtering half of an absolute value of a measure of flow of breathable gas with a second time constant, the second time constant being larger than the first time constant.

9. The apparatus of claim 8 wherein the proportion comprises approximately seventy percent.

10. The apparatus of claim 1 wherein the controller is further configured to indicate a severity of the hypopnea with the measure of area.

11. The apparatus of claim 1 wherein the detecting comprises comparing the measured area with a threshold chosen to be approximately indicative of a desaturation of blood oxygen of at least four percent.

12. The apparatus of claim 1 wherein the controller is further configured to detect a measure of flow limitation from the data and wherein the detection of the hypopnea is further based on the measure of flow limitation being indicative of obstruction.

13. The apparatus of claim 1 further comprising a flow sensor and wherein the controller is further configured to determine the measured flow of breathable gas with the flow sensor.

14. The apparatus of claim 13 further comprising:

a flow generator configured to produce a breathable gas for a patient at a pressure above atmospheric pressure;

wherein the controller is further configured to control the flow generator to produce the breathable gas according to a pressure therapy regime based on the detected hypopnea.

15. An apparatus to detect a hypopnea from a measured flow of breathable gas, the apparatus comprising:

a controller having at least one processor to access data representing a measured flow of breathable gas, the controller being further configured to;

determine a long-term measure of ventilation from the data;

determine a short-term measure of ventilation from the data;

determine a threshold as a proportion of the long-term measure of ventilation;

calculate an extent of a hypopnea as a function of the short-term measure of ventilation and the threshold; and

indicate a severity of the hypopnea with the calculated extent.

16. The apparatus of claim 15 wherein the controller is configured to indicate the severity by outputting a value of the calculated extent to an output device.

17. The apparatus of claim 16 wherein the controller calculates the extent by calculating an area bounded by first and second crossings of the short-term measure of ventilation and the threshold.

18. The apparatus of claim 17 wherein the controller is further configured to compare the calculated area with a threshold chosen to be approximately indicative of a desaturation of blood oxygen of at least four percent.

19. The apparatus of claim 15 further comprising a flow sensor and wherein the controller is further configured to determine the measured flow of breathable gas with the flow sensor.

20. The apparatus of claim 19 further comprising:

a flow generator configured to produce a breathable gas for a patient at a pressure above atmospheric pressure;

wherein the controller is further configured to control the flow generator to produce the breathable gas according to a pressure therapy regime based on the detected hypopnea.

21. The apparatus of claim 20 wherein the controller is further configured to detect a measure of flow limitation from the data and wherein the indicating the detection of the hypopnea is further based on the measure of flow limitation being indicative of obstruction.