Method and apparatus for determining conditions of biological tissues

• US 20060037615A1
• Filed: 04/15/2005
• Published: 02/23/2006
• Est. Priority Date: 04/20/2000
• Status: Active Grant

• Current Assignee: Respiri (Israel) Ltd.
• Original Assignee: PulmoSonix Pty., Ltd. (Spenda Ltd.)
• Inventors: Samuhel, Frank, Camilleri, Peter, Ramsden, Clive Andrew, Wilson, Jacqueline Anne, Berger, Philip John, Wilkinson, Malcolm Howard
• Granted Patent: US 7,708,697 B2
• Time in Patent Office: Days
• US Class Current: 128/204.230
• CPC Class Codes: A61B 5/08 Detecting, measuring or recording devices for evaluating the respiratory organs A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/085 Measuring impedance of respiratory organs or lung elasticity
• CPC Class Codes: A61B 5/4818 Sleep apnoea
• CPC Class Codes: A61B 5/7257 using Fourier transforms
• CPC Class Codes: A61B 8/08 Detecting organic movements or changes, e.g. tumours, cysts, swellings A61B8/02 - A61B8/06 take precedence
• CPC Class Codes: A61M 16/0006 with means for creating vibrations in patients' airways
• CPC Class Codes: A61M 16/0051 with alarm devices
• CPC Class Codes: A61M 16/026 specially adapted for predicting, e.g. for determining an information representative of a flow limitation during a ventilation cycle by using a root square technique or a regression analysis
• 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 2016/0039 in the inspiratory circuit
• CPC Class Codes: A61M 2205/3375 Acoustical, e.g. ultrasonic, measuring means
• CPC Class Codes: A61M 2230/04 Heartbeat characteristics, e.g. ECG, blood pressure modulation
• CPC Class Codes: A61M 2230/205 partial oxygen pressure (P-O2)
• CPC Class Codes: A61M 2230/65 Impedance, e.g. conductivity, capacity

Abstract

Airway monitoring apparatus 30 includes a driver 6 for applying sound in the audible frequency range to the airway of a subject and a detector 7 for monitoring the response of the airway, e.g. by detecting transmitted sound signal components and/or reflected sound signal components. Variations in the detected sound signal, e.g. energy, due to attenuation of the signal, give an indication of the state of the airway, e.g. airway patency, and can be used to monitor sleep-disordered breathing events, such as apnea and hypopnea, and to provide a breathing event index, e.g. AHI. The apparatus may provide servo-control for a respiratory assist device, such as a positive airway pressure device, so as to provide an appropriate pressure level setting. It may allow for home use of such devices and for home titration. It may also assist in discriminating central and obstructive breathing events, and in providing a measure of airway resistance.

Claims

1. Apparatus for monitoring airway patency, the apparatus including:

a sound generator for applying a sound signal in the audible frequency spectrum to an airway;

a detector for detecting the sound signal after it has travelled through at least a portion of the airway; and

an analyser for monitoring airway patency based on variations in the detected sound signal.

2. Apparatus according to claim 1, wherein the airway may include one or more of:

the buccal cavity, the nasal cavity, the pharyngeal region, the laryngeal region and the tracheal region.

3. The apparatus of claim 1, wherein the detector detects sound transmitted through said airway portion.

4. The apparatus of claim 1, wherein the detector detects sound reflected back from said airway portion.

5. The apparatus of claim 1, wherein the sound signal is applied through one or more of the following:

(a) one of the nares;

(b) both of the nares;

(c) the mouth;

(d) the mouth and the nares.

6. The apparatus of claim 1, wherein the sound signal is applied through one of:

(a) a face mask;

(b) a nose mask

(c) a mouth mask

(d) a nasal plug

(e) a nasal cannula.

7. The apparatus of claim 1, wherein the sound signal is applied:

(a) to one nares and detected from the other nares;

(b) to both nares and detected from both

(c) orally and detected orally

(d) to the nose and/or mouth and detected in the other or both.

8. The apparatus of claim 1, wherein a sound detector is positioned in one or more of:

the chest, back, abdomen or the region of the suprasternal notch.

9. The apparatus of claim 1, wherein the applied sound signal is based on pseudo-random noise.

10. The apparatus of claim 9, wherein the sound generator generates sound signals based on a repeating noise signal sequence, the length of the repeated sequence being such that the repetition is substantially unperceived by the subject whose airway is being monitored.

11. The apparatus of claim 1, wherein the sound generator generates sound signals based on a repeating noise signal sequence, and wherein the repeated sequence is divided into a plurality of signal packets to allow for processing of the detected signal at a rate higher than the repeated sequence length.

12. The apparatus of claim 1, wherein the analyser includes a correlator for performing a cross-correlation of the detected sound signal with a reference signal.

13. The apparatus of claim 1, wherein the analyser determines an impulse response.

14. The apparatus of claim 1, wherein the analyser determines a frequency response.

15. The apparatus of claim 1, wherein the analyser determines a response to a combination of the airway and the monitoring apparatus.

16. The apparatus of claim 1, wherein the analyser determines a peak value in a signal response to determine patency.

17. Apparatus according to claim 16, wherein the apparatus determines the position of a peak in an impulse response and monitors the strength of the impulse response at that point over time in order to determine patency.

18. Apparatus according to claim 16, wherein the apparatus tracks a peak in an impulse response over time, and monitors the strength of the peak in order to determine patency.

19. The apparatus of claim 1, wherein the analyser determines patency based on a variation in the profile of a response signal determined from said detected signal.

20. The apparatus of claim 19, wherein the analyser compares characteristics of the response signal in at least two regions to determine patency.

21. The apparatus of claim 1, wherein the analyser compares response characteristics of regions proximal and distal to an obstruction or partial obstruction to determine patency.

22. Apparatus according to claim 1, wherein the apparatus monitors an energy shift in the detected response signal.

23. Apparatus according to claim 3, wherein the applied sound signal comprises frequencies according to one or more of the following:

(a) frequencies greater than about 100 Hz

(b) frequencies greater than about 400 Hz

(c) frequencies greater than about 500 Hz

(d) frequencies less than about 2 kHz

(e) frequencies less than about 1500 kHz

(f) frequencies less than about 1 kHz

(g) frequencies between about 500 Hz and about 1500 Hz

(h) frequencies between about 500 Hz and about 800 Hz.

24. Apparatus according to claim 1, wherein the applied sound signal has a frequency bandwidth according to one or more of the following:

(a) a bandwidth that substantially prevents the perception of an unpleasant tonal quality in the applied sound signal

(b) a bandwidth of about 150 Hz or greater

(c) a bandwidth about 250 Hz or greater

(d) a bandwidth of about 300 Hz or greater

(e) a bandwidth of between about 200 and about 1000 Hz.

25. Apparatus according to claim 3, wherein said sound signal has a central frequency between about 600 Hz and about 800 Hz and a bandwidth of between about 300 Hz and about 1000 Hz.

26. Apparatus according to claim 4, wherein said sound signal has a frequency bandwidth from about 100 Hz to about 10 kHz.

27. Apparatus according to claim 1, the applied sound signal is based on one or more of:

(a) a frequency characteristic of the patient airway; and

(b) a resonant frequency of the airway that is substantially stable during open and closed mouth events.

28. Apparatus according to claim 1, including a tuner control for determining frequency characteristics for the applied sound signal that provide an optimum response signal.

29. Apparatus according to claim 1, including means for monitoring the signal level of the detected signal and for rejecting signal data above a threshold value.

30. Apparatus according to claim 29, wherein when signal data is rejected, the apparatus outputs patency data based on previous patency data.

31. Apparatus according to claim 29, wherein the detected sound signal is divided into a plurality of data packets, each packet being used to determine a patency value, and wherein when a packet includes sampled data above a threshold value, the data from the packet is rejected.

32. Apparatus according to claim 29, wherein the detected sound signal is divided into a plurality of packets, each packet being used to determine a patency value and each including a number of data samples of the detected sound signal, and wherein when a detected data sample of a packet is above a threshold value, the detected data sample is adjusted to a lower value.

33. Apparatus according to claim 32, wherein a patency value based on an adjusted data packet is adjusted to compensate for said adjusted data samples.

34. Apparatus according to claim 1, including means for determining the fast Fourier transform of the detected sound signal and for attenuating frequency components that exceed a threshold value.

35. Apparatus according to claim 1, wherein the analyser determines the location of an obstruction based on the detected sound signal.

36. Apparatus according to claim 35, wherein the analyser determines an obstruction position based on a comparison of at least two portions of the response signal.

37. Apparatus according to claim 1, including a sensor for determining airflow in the airway.

38. Apparatus according to claim 37, wherein the analyser discriminates between a central breathing event and an obstructive breathing event based on patency and airflow measurements.

39. Apparatus according to claim 1, wherein the analyser discriminates between an apneic event and a hypopneic event based on the degree of patency of the airway.

40. Apparatus according to claim 1, wherein the analyser determines one or more of the following:

(a) an obstruction when patency is low;

(b) a partial obstruction when patency is reduced;

(c) an obstruction when patency is low and airflow has ceased;

(d) a partial obstruction when patency and airflow are reduced;

(e) a cessation or reduction of an obstruction when patency rises;

(f) a central apnea when patency is high and airflow has ceased;

(g) an obstructive apnea when patency is low and airflow is reduced;

(h) a central hypopnea when patency remains constant and airflow has ceased;

(i) an obstructive hypopnea when patency and airflow are reduced.

41. Apparatus according to claim 1, wherein the analyser issues an alarm when patency is below a threshold value.

42. Apparatus for the monitoring of sleep-disordered breathing, including patency apparatus according to claim 1, wherein sleep-disordered breathing is determined based on detected patency.

43. Apparatus for providing a sleep-disordered breathing index, including patency apparatus according to claim 1, including an index calculator for counting the number of breathing event that occur in a set time period based on at least the detected patency of the airway.

44. Respiratory assist apparatus including patency apparatus according to claim 1, wherein a respiratory assist function is controlled based on detected patency.

45. Positive airway pressure apparatus including patency apparatus according to claim 1, wherein the determined patency of the airway is used to control the level of positive airway pressure applied to the patient.

46. Apparatus for determining airway resistance including patency apparatus according to claim 1, wherein airway resistance is determined based on airway patency.

47. A method of monitoring airway patency, including the steps of:

applying a sound signal in the audible frequency spectrum to an airway;

detecting the sound signal after it has travelled through the airway; and

analysing the sound signal to monitor patency of the airway based on variations in the detected sound signal.

48. Sleep-disordered breathing monitoring apparatus, including a sound generator for applying a sound signal in the audible frequency spectrum to the airway of the subject, a detector for detecting a response to the applied sound signal, and an analyser for determining the occurrence of a sleep-disordered breathing event based on the detected response.

49. A method of diagnosing sleep disordered breathing, including the steps of:

applying a sound signal in the audible frequency spectrum to an airway;

detecting a response to the sound signal;

determining one or more physiological parameters; and

analysing variations in the response and said one or more physiological parameters to determine sleep-disordered breathing events.

50. Respiratory assist apparatus, the apparatus including a sound generator for applying a sound signal in the audible frequency spectrum to the airway of the subject, a detector for detecting a response to the applied sound signal, and an analyser for determining the need for a respiratory assist action based on the detected response.

51. A method of titrating a positive airway pressure respiratory assist device, the method including the steps of:

applying positive pressure to an airway;

applying a sound signal in the audible frequency spectrum to the airway;

detecting a response to the sound signal;

determining one or more physiological parameters; and

analysing variations in the detected response and said one or more physiological parameters and varying the amount of positive pressure applied to the airway to provide a suitable level of positive pressure to the patient.

52. Apparatus for determining a sleep-disordered breathing index, the apparatus including a sound generator for applying a sound signal in the audible frequency spectrum to the airway of a subject, a detector for detecting a response to the applied sound signal, and an analyser for determining the occurrence of a sleep-disordered breathing event based on the detected response and for determining a sleep-disordered breathing index based on the frequency of the determined events.

53. Apparatus for determining airway resistance, the apparatus including:

a sound generator for applying a sound signal in the audible frequency spectrum to an airway;

a detector for detecting a response to the applied sound signal; and

an analyser for determining airway resistance based on the detected response.

54. Apparatus for monitoring airway patency, the apparatus including:

a sound generator for applying a sound signal in the audible frequency spectrum to an airway, the sound signal being based on pseudo-random noise;

a detector for detecting the sound signal after it has travelled through at least a portion of the airway;

a cross-correlator for determining an impulse response based on the detected signal and a reference signal related to the applied sound signal; and

an analyser for monitoring a patency state for the airway based on a variation in the impulse response caused by an interaction of the applied sound signal with a portion of the airway whose patency is compromised.

55. Apparatus for monitoring airway patency, the apparatus including:

a sound generator for applying a sound signal in the audible frequency spectrum to at least a portion of an airway, the airway portion having an end proximal to the sound generator and an end distal from the sound generator;

a detector for detecting a resulting sound signal at said distal end of said airway portion; and

an analyser for determining patency for the airway portion based on the detected signal.

56. Apparatus for monitoring airway patency, the apparatus including:

a sound generator for applying a sound signal in the audible frequency spectrum to at least a portion of an airway, the airway portion having an end proximal to the sound generator and an end distal from the sound generator;

a detector for detecting a resulting sound signal at said proximal end of said airway portion, said sound signal including components of said applied sound signal that are reflected back to said proximal end of said airway; and

an analyser for determining patency for the airway portion based on the detected signal.

57. Apparatus for monitoring a state of an airway, the apparatus including:

a sound generator for applying a sound signal in the audible frequency spectrum to an airway;

a detector for detecting the sound signal after it has travelled through at least a portion of the airway; and

an analyser for monitoring the state of the airway based on variations in the detected sound signal.

58. A method of determining characteristics of biological tissue in situ, including:

introducing a sound to the tissue at first position;

detecting the sound at another position spaced from the first position after it has travelled through the tissue;

calculating the velocity and attenuation of sound that has travelled through the tissue from the first position to another position; and

correlating the velocity and attenuation of the detected sound to characteristics of the biological tissue.

59. A method according to claim 58 for determining a state of the upper airways in a respiratory tract in a patient in situ, said method including:

introducing a sound at first position in the upper airways;

detecting the sound after it has travelled through the upper airways at another position spaced from the first position;

calculating the velocity and attenuation of the sound travelled through the upper airways from the first position to another position; and

correlating the velocity and attenuation of the sound to the state of the upper airways.

60. An apparatus for determining characteristics of biological tissues, the apparatus including:

a sound generating device which generates a sound;

a recording device which records the sound after it has travelled from one position of the biological tissue, through the tissue and to another position of the tissue; and

an analysis device which determines characteristics of the sound that has travelled through the tissue.