METHODS AND APPARATUS FOR CALIBRATING RESPIRATORY EFFORT FROM PHOTOPLETHYSMOGRAPH SIGNALS

• US 20110270114A1
• Filed: 04/30/2010
• Published: 11/03/2011
• Est. Priority Date: 10/03/2008
• Status: Active Grant

• Current Assignee: Nellcor Puritan Bennett Ireland
• Original Assignee: Nellcor Puritan Bennett Ireland
• Inventors: Addison, Paul Stanley, Watson, James N.
• Granted Patent: US 9,155,493 B2
• Time in Patent Office: Days
• US Class Current: 600/533
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/087 Measuring breath flow
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/4818 Sleep apnoea
• CPC Class Codes: A61B 5/726 using Wavelet transforms

Abstract

Breathing effort of a patient, as determined (for example) from a photoplethysmograph (“PPG”) signal from the patient, can be calibrated in relation to air pressure in the patient'"'"'s respiratory system. This calibration can be done by subjecting the patient to varying amounts of breathing resistance; and for each such amount, concurrently measuring (1) air pressure in the respiratory system (e.g., in the oral/nasal cavity) and (2) breathing effort (from the PPG signal). Use can be made of this calibration, e.g., during a sleep study of the patient. During such a study, breathing effort, again determined from the PPG signal and occurring, for example, during an apneic event of the patient, can be used to infer air pressure in the respiratory system by using the above calibration.

Claims

1. A method of calibrating respiratory effort of a patient comprising:

using a pressure sensor to measure air pressure in the patient'"'"'s oral/nasal cavity during breathing with each of a plurality of successive different amounts of resistance to breathing to produce an oral/nasal pressure signal value for each respective amount of breathing resistance;

using respiratory effort monitoring apparatus to acquire a respiratory effort signal from the patient during breathing with each respective amount of breathing resistance; and

using respiratory effort signal processing circuitry to determine from the respiratory effort signal for each respective amount of breathing resistance a respective breathing effort signal value.

2. The method defined in claim 1 further comprising:

using storage circuitry to store a correlation between each oral/nasal pressure signal value and the breathing effort signal value concurrent with that respective oral/nasal pressure signal value.

3. The method defined in claim 2 wherein each oral/nasal pressure signal value is produced while the patient is awake.

4. The method defined in claim 3 further comprising:

using respiratory effort monitoring apparatus to acquire a respiratory effort signal from the patient while asleep;

using respiratory effort signal processing circuitry to determine from the respiratory effort signal from the sleeping patient at least one breathing effort signal value for the sleeping patient; and

using the correlation to convert the breathing effort signal value for the sleeping patient to a respiratory system air pressure signal value for the sleeping patient.

5. The method defined in claim 4 further comprising:

outputting the respiratory system air pressure signal value for the sleeping patient in human-readable form.

6. The method defined in claim 1 wherein the using respiratory effort signal processing circuitry comprises:

producing scalogram signals representing a scalogram of the respiratory effort signal;

analyzing the scalogram signals to identify breathing band signals in the scalogram signals; and

determining a breathing band amplitude signal value as an indication of breathing effort.

7. The method defined in claim 1 further comprising:

using breathing resistance apparatus to subject the patient to the successive different amounts of resistance to breathing.

8. The method defined in claim 7 wherein the using breathing resistance apparatus comprises:

applying the breathing resistance apparatus to the patient so that the patient can only breathe through an air flow passageway through the breathing resistance apparatus.

9. The method defined in claim 8 wherein the using breathing resistance apparatus further comprises:

varying size of the air flow passageway through the breathing resistance apparatus to subject the patient to the successive different amounts of resistance to breathing.

10. The method defined in claim 1 wherein the using a pressure sensor comprises:

placing the pressure sensor in the patient'"'"'s mouth.

11. The method defined in claim 1 wherein the using respiratory effort monitoring apparatus comprises:

using photoplethysmograph (“

PPG”

) monitoring apparatus.

12. Apparatus for monitoring sleep apnea of a patient comprising:

means for subjecting the patient, while awake, to a plurality of different amounts of resistance to breathing;

means for measuring air pressure in the patient'"'"'s oral/nasal cavity to determine an air pressure value for each amount of resistance to breathing;

means for using a respiratory effort signal from the patient to measure the patient'"'"'s breathing effort to determine a breathing effort value for each air pressure value and thereby a relationship between breathing effort and air pressure;

means for continuing to use the respiratory effort signal from the patient, while asleep, to determine apneic breathing effort values during apneic events; and

means for using the relationship to determine an air pressure that corresponds to each apneic breathing effort value.

13. The apparatus defined in claim 12 wherein the means for using a respiratory effort signal comprises:

means for producing scalogram signals representing a scalogram of the respiratory effort signal.

14. The apparatus defined in claim 13 wherein the means for using a respiratory effort signal further comprises:

means for analyzing the scalogram signals

to identify breathing band signals in the scalogram signals.

15. The apparatus defined in claim 14 wherein the means for using a respiratory effort signal still further comprises:

means for determining amplitude of the breathing band signals as an indication of breathing effort.

16. The apparatus defined in claim 12 further comprising:

means for outputting a human-readable indication of the air pressure that corresponds to each apneic breathing effort value.

17. The apparatus defined in claim 12 wherein the means for subjecting comprises:

means for requiring the patient to breathe only through an air flow passageway through controllable breathing resistance apparatus.

18. The apparatus defined in claim 17 wherein size of the air flow passageway is variable to vary the amount of breathing resistance the breathing resistance apparatus subjects the patient to.

19. The apparatus defined in claim 12 wherein the means for measuring comprises:

a pressure sensor adapted for placement in the patient'"'"'s mouth.

20. The apparatus defined in claim 12 wherein the means for using a respiratory effort signal comprises:

means for using a photoplethysmograph (“

PPG”

) signal.