Detection and monitoring device

• US 4,306,567 A
• Filed: 01/25/1980
• Issued: 12/22/1981
• Est. Priority Date: 12/22/1977
• Status: Expired due to Term

• Current Assignee: Clinical Development Corporation
• Original Assignee: Plasmedics Incorporated
• Inventors: Krasner, Jerome L.
• Primary Examiner(s): Michell, Robert W.
• Assistant Examiner(s): Jaworski, Francis J.
• Application Number:
  US06/115,403
• Time in Patent Office: 697 Days
• Field of Search: 128/670-671, 128/691-694, 128/661-663, 128/715, 128/721-724
• US Class Current: 600/484
• CPC Class Codes: A61B 5/0816 Measuring devices for examining respiratory frequency measuring frequency of electric signals G01R23/00
• CPC Class Codes: A61B 5/113 occurring during breathing
• CPC Class Codes: A61B 7/003 Detecting lung or respiration noise

Abstract

One or more physiological rhythmic functions can be monitored by detecting pressure waves within a predetermined, relatively narrow, frequency band associated with each of said functions, generating a corresponding signal representative of said pressure waves associated with each of said functions and demodulating the signal to detect any amplitude modulation frequency related to the rhythmic rate of each of said functions.

Claims

1. A system for monitoring over relatively long periods of time, the rate of at least one physiological rhythmic function of a subject, said system comprising, in combination:

detection means for detecting acoustical energy generated by said subject within a predetermined, relatively narrow acoustical frequency band, characteristic of and unique with respect to said function, said detection means being attachable to said subject allowing the subject to move and generate motion artifacts;

generating means for generating an electrical signal representative of the acoustical energy within said frequency band and detected from the subject;

demodulating means for demodulating said electrical signal so as to produce a demodulated electrical signal and so as to detect any periodic amplitude modulation frequency of said electrical signal;

means for distinguishing between the portions of the demodulated electrical signal representative of acoustical energy detected from the subject and attributed to said function and at least some of those portions of the demodulated electrical signal representative of acoustical energy detected and attributed to said motion artifacts; and

means for generating a function rate signal as a function of the portions of the demodulated electrical signal representative of the acoustical energy detected from the subject and attributed to said physiological function;

wherein the portions of the demodulated electrical signal representative of acoustical energy detected from the subject and attributed to said physiological function encompasses a band of frequencies which includes the frequency at which the optimum signal-to-noise ratio occurs in order to distinguish between those portions of the demodulated electrical signal generated by acoustical energy detected from the subject and attributed to said function at typical, normal amplitude levels and spurious electrical signals generated by acoustical energy within said band and attributed to said motion artifacts.

2. A system in accordance with claim 1, wherein said physiological function is the cardiac rate of said subject and said frequency band includes frequencies between about 30 Hz and about 90 Hz.

3. A system in accordance with claim 2, wherein said generating means includes bandpass filter means having a center frequency at about 45 Hz so as to provide said optimum signal-to-noise ratio.

4. A system in accordance with claim 1, wherein said means for distinguishing includes means for generating a pulse train in response to said demodulated signal, the repetition rate of said pulse train being representative of said periodic amplitude modulated frequency.

5. A system in accordance with claim 4, wherein said demodulating means includes means for rectifying said electrical signal so as to produce a rectified signal and means for generating said demodulated electrical signal representative of the envelope of the rectified signal, and said means for generating said pulse train includes detection means for providing an output signal so long as the amplitude of said demodulated signal exceeds some predetermined amplitude above spurious noise.

6. A system according to claim 5, wherein said detection means provides an output signal so long as the amplitude of said demodulated signal is below some second predetermined amplitude below noise associated with said motion artifacts and above the first-mentioned predetermined amplitude.

7. A system according to claim 5, wherein the pulse width of each pulse of said pulse train associated with the physiological function is within a predetermined time range, and said system further includes means for determining the repetition rate of those pulses within said time range.

8. A system according to claim 7, wherein said means for determining the repetition rate includes means for providing said function rate signal as an analog signal, the amplitude of said analog signal being a function of said repetition rate of those pulses within said time range.

9. A system according to claim 8, further including indication means for indicating when the amplitude of said analog signal drops below a first predetermined value or rises above a second predetermined value.

10. A system according to claim 9, wherein said rate of said physiological function is the cardiac rate of said subject, and the amplitude of said analog signal below said first predetermined value corresponds to a bradycardia condition and an amplitude of said analog signal above said second predetermined value corresponds to a tachycardia condition.

20. A system according to claim 4, wherein the acoustical energy generated by said subject and attributed to the respiration function is generated by the nonlaminar flow of air through the trachea of said subject.

11. A system for monitoring over a relatively long period of time the respiration rate of a subject, said system comprising, in combination:

detection means for detecting acoustical energy generated by said subject within a predetermined, relatively narrow acoustical frequency band characteristic of and unique with respect to the respiration function of the subject, said detection means being attachable to said subject allowing the subject to move and generate motion artifacts;

generating means for generating an electrical signal representative of the acoustical energy detected from the subject within the frequency band;

demodulation means for demodulating said electrical signal so as to produce a demodulated electrical signal and so as to detect any periodic amplitude modulation frequency of the electrical signal;

means for distinguishing between those portions of the demodulated electrical signal representative of acoustical energy detected from the subject and attributed to respiration and at least some of those portions of the demodulated electrical signal representative of acoustical energy detected and attributed to said motion artifacts; and

means for generating a respiration rate signal as a function of the portions of the demodulated signal representative of acoustical energy detected from the subject and attributed to respiration;

wherein the portions of the demodulated electrical signal representative of acoustical energy detected from the subject and attributed to respiration encompasses a band of frequencies which includes the frequency at which optimum signal-to-noise ratio occurs so as to easily distinguish between those portions of the demodulated electrical signal representative of acoustical energy detected from the subject and attributed to respiration at typical, normal amplitude levels and spurious electrical signals generated by acoustical energy within said band and attributed to said motion artifacts.

12. A system in accordance with claim 11, wherein said frequency band includes frequencies between about 300 Hz and about 600 Hz.

13. A system in accordance with claim 12, wherein said generating means includes bandpass filter means having a center frequency selected to provide said optimum signal-to-noise ratio.

14. A system in accordance with claim 13, wherein said center frequency is about 400 Hz.

15. A system according to claim 11, wherein said means for distinguishing between those portions of said demodulated signal includes means for generating a pulse train, the repetition rate of which is representative of said periodic amplitude modulated frequency and means for determining the repetition rate of those pulses having widths within a predetermined range of time durations.

16. A system according to claim 15, wherein said means for determining said repetition rate includes means for providing said respiration rate signal as an analog signal the amplitude of said analog signal being a function of said repetition rate of those pulses having widths within said range.

17. A system according to claim 16, further including indication means for indicating when the amplitude of said analog signal drops below a predetermined value.

18. A system according to claim 16, wherein said predetermined value corresponds to the cessation of breathing for a predetermined period of time.

19. A system according to claim 15, wherein said predetermined range of time durations is between about 300 and about 600 milliseconds.

21. A system for simultaneously monitoring over a relatively long period of time the respiration rate and heart rate of a subject, said system comprising, in combination:

an acoustical detector for detecting acoustical energy generated by said subject within a first predetermined, relatively narrow acoustical frequency band characteristic and unique with respect to the respiration function of the subject and within a second predetermined relatively narrow acoustical frequency band characteristic and unique with respect to the cardio-vascular function of the subject;

first generating means for generating a first electrical signal representative of the acoustical energy detected from the subject within said first frequency band;

second generating means for generating a second electrical signal representative of the acoustical energy detected from the subject within said second frequency band;

first demodulation means for demodulating said first electrical signal so as to produce a first demodulated electrical signal and so as to detect any periodic amplitude modulation frequency of the first electrical signal as a function of the respiration rate of the respiration rate of the subject;

second demodulation means for demodulating said second electrical signal so as to produce a second demodulated electrical signal and so as to detect any periodic amplitude modulation frequency of the second electrical signal as a function of the heart rate of the subject; and

means coupled to each of the outputs of said first and second demodulator means for respectively monitoring each of said first and second demodulated signals independently of the presence of acoustical energy arising from vocal expression.

22. A system according to claim 21, further including means for selectively disabling the output of said second demodulator upon a vocal expression above a predetermined threshold.

23. A system according to claim 22, wherein said means for selectively disabling the output of said second demodulator means includes detection means for detecting signals associated with vocal expression when present with the signal associated with the cardio-vascular function and means for gating said signal associated with the cardio-vascular function so as to reject those portions of said signal associated with the cardio-vascular function which inlcudes signals associated with said vocal expression.

24. In combination with a respiratory device of the type including a tube insertable through the trachea of a subject, an improved device for monitoring the respiration rate of said subject over relatively long periods of time, said device comprising, in combination:

detection means, coupled to said tube, for detecting acoustical energy generated by said subject through said tube within a predetermined relatively narrow bandwidth characteristic of and unique with respect to the respiration function of the subject;

generating means for generating an electrical signal representative of the acoustical energy detected from the subject within the frequency bandwidth;

demodulation means for demodulating said electrical signal so as to produce a demodulated signal and so as to detect any periodic amplitude modulation frequency of the electrical signal;

means for distinguishing between those portions of the demodulated electrical signal representative of acoustical energy detected from the subject and attributed to respiration and those portions of the demodulated electrical signal representative of acoustical energy detected and attributed to motion artifacts; and

means for generating a respiration rate signal as a function of the portions of the demodulated electrical signal representative of the acoustical energy detected from the subject and attributed to the respiration rate;

wherein the portions of the demodulated electrical signal representative of acoustical energy detected from the subject and attributed to respiration encompasses a band of frequencies which includes the frequency at which the optimum signal-to-noise ratio occurs so as to easily distinguish between those portions of the demodulated electrical signal detected from the subject and attributed to respiration and spurious electrical signals generated by acoustical energy within said band and attributed to said motion artifacts.

25. In a device according to claim 24, wherein said tube is an endotracheal tube.

26. In a device according to claim 24, wherein said tube is a tracheostomy tube.