Phonospirometry for non-invasive monitoring of respiration

• US 6,241,683 B1
• Filed: 02/22/1999
• Issued: 06/05/2001
• Est. Priority Date: 02/20/1998
• Status: Expired due to Term

• Current Assignee: Institut De Recherches Cliniques De Montreal, McGill University
• Original Assignee: Institut De Recherches Cliniques De Montreal, McGill University
• Inventors: Macklem, Peter T., Kelly, Suzanne M., Kolmaga, Krzystof, Que, Cheng-Li, Durand, Louis-Gilles
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US09/255,003
• Time in Patent Office: 834 Days
• Field of Search: 600/529, 600/532-4, 600/538, 600/586
• US Class Current: 600/529
• CPC Class Codes: A61B 5/091 Measuring volume of inspired or expired gases, e.g. to determine lung capacity
• CPC Class Codes: A61B 7/003 Detecting lung or respiration noise

Abstract

To compensate for the poor signal-to-noise ratio when transforming a patient tracheal sound signal into a respiration flow signal, the transformed signal is used when the sound signal is above a threshold, and interpolated values are used when the sound signal is below the threshold. A volume of breath signal is reliably obtained. Respiration start/stop is detected either by analyzing the sound signal or by physical measurement of the patient. A wearable device incorporating the sound signal processing method can provide an immediate indication or alarm when the volume of breath signal indicates a condition requiring medical attention.

Claims

1. A method for obtaining a volume of respiration signal from a sound signal representing respiration, the method comprising:

detecting respiration start/stop;

comparing an intensity of said sound signal to a threshold to determine whether said sound signal intensity is sufficiently strong with respect to background noise so as to provide a reliable measure of tracheal flow;

transforming said sound signal to a flow signal;

interpolating values for said flow signal when said sound signal intensity is below said threshold; and

integrating said flow signal and said interpolated values of said flow signal over at least one of an inspiration cycle and an expiration cycle to obtain a volume of breath signal for said at least one cycle.

2. The method as claimed in claim 1, wherein said at least one cycle is inspiration, and said interpolating comprises:

firstly interpolating said flow signal during inspiration from a point of detecting said respiration start/stop at which said flow is determined to be zero until said sound signal intensity reaches said threshold and has a value determined by said transforming; and

secondly interpolating said flow signal at an end of said inspiration cycle as said sound signal intensity drops below said threshold at an end of inspiration and a zero flow value point determined using a function continuous between said flow signal value at a point where said sound signal intensity drops below said threshold and said flow signal value at a point where said sound signal intensity rises above said threshold at a beginning of expiration.

3. The method as claimed in claim 1, wherein said volume of breath signal is obtained only for said inspiration cycle, said volume of breath signal for said expiration cycle over a large number of cycles being equal to said volume of breath signal for said inspiration cycle.

4. The method as claimed in claim 3, wherein said steps of comparing and transforming involve analysis which is the same for both inspiration and expiration.

5. The method as claimed in claim 2, wherein said firstly and said secondly interpolating comprises linear interpolating.

6. The method as claimed in claim 1, further comprising a step of averaging said volume signal over time to obtain a tidal volume signal.

7. The method as claimed in claim 3, further comprising a step of averaging said volume signal over time to obtain a tidal volume signal.

8. The method as claimed in claim 1, wherein said step of detecting respiration start/stop comprises analyzing said sound signal.

9. The method as claimed in claim 1, wherein said step of detecting respiration star/stop comprises physically measuring at least one of chest and abdomen position or motion.

10. The method as claimed in claim 1, further comprising a step of monitoring a time of said respiration start/stop to obtain a respiratory frequency signal.

11. The method as claimed in claim 1, further comprising a step of averaging said flow signal during inspiration and generating a mean inspiratory flow signal.

12. The method as claimed in claim 1, further comprising a step of calibrating a sound signal to flow signal transform function by measuring treacheal flow directly while recording said sound signal over a period of time and setting parameters of said transform function to provide flow values corresponding to said measured tracheal flow.

13. The method as claimed in claim 3, further comprising a step of calibrating a sound signal to flow signal transform function by measuring tracheal flow directly while recording said sound signal over a period of time and setting parameters of said transform function to provide flow values corresponding to said measured tracheal flow.

14. An apparatus for non-invasive monitoring of respiration comprising:

at least one microphone for obtaining a sound signal from a person, said sound signal representing respiration;

means for detecting inspiration start and stop;

means for transforming said sound signal to a flow signal, said transforming means receiving data from transfer function register means and threshold value register means;

means for generating interpolated values for said flow, signal when said sound signal is below said threshold value; and

integrator means for integrating said flow signal to produce a volume of respiration signal.

15. The apparatus as claimed in claim 14, further comprising an alarm circuit for processing said volume of respiration signal and generating an alarm signal when said volume of respiration signal has characteristics representing a condition in need of medical attention.

16. A method for obtaining at least one of a diagnosis and a prognosis of a respiratory disease comprising the steps of:

placing at least one microphone on a patient to obtain a sound signal from respiration of said patient;

processing said sound signal to obtain a volume of respiration signal;

monitoring said volume of respiration signal over time;

analyzing said volume signal over time to obtain at least one parameter indicative of said diagnosis and/or prognosis.

17. The method as claimed in claim 16, wherein said step of processing comprises:

detecting respiration start/stop;

comparing an intensity of said sound signal to a threshold to determine whether said sound signal intensity is sufficiently strong with respect to background noise so as to provide a reliable measure of tracheal flow;

transforming said sound signal to a flow signal;

interpolating values for said flow signal when said sound signal intensity is below said threshold; and

integrating said flow signal and said interpolated values of said flow signal over at least one of an inspiration cycle and an expiration cycle to obtain a volume of breath signal for said at lest one cycle.

18. The method as claimed in claim 17, wherein said at least one cycle is inspiration, and said interpolating comprises:

firstly interpolating said flow signal during inspiration from a point of detecting said respiration start/stop at which said flow is determined to be zero until said sound signal intensity reaches said threshold and has a value determined by said transforming; and

secondly interpolating said flow signal at an end of said inspiration cycle as said sound signal intensity drops below said threshold at an end of inspiration and a zero flow value point defined using a function continuous between said flow signal value at a point where said sound signal intensity drops below said threshold and said flow signal value at a point where said sound signal intensity rises above said threshold at a beginning of expiration.

19. The method as claimed in claim 18, wherein said volume of breath signal is obtained only for said inspiration cycle, said volume of breath signal for said expiration cycle over a large number of cycles being to said volume of breath signal for said inspiration cycle.

20. The method as claimed in claim 17, further comprising steps of:

attaching a wearable eye device to said patient, said device having signal processing means for carrying out said step of processing; and

analyzing said volume of breath signal and generating an alarm when said volume of respiration signal has characteristics representing a condition in need of medical attention.