PHYSIOLOGICAL MONITORING SYSTEM

• US 3,608,542 A
• Filed: 06/12/1970
• Issued: 09/28/1971
• Est. Priority Date: 06/12/1970
• Status: Expired due to Term

• Current Assignee: Allan F. Pacela, Fredrick J. Savaglio
• Original Assignee: Allan F. Pacela, Fredrick J. Savaglio
• Inventors: Savaglio, Fredrick J., Pacela, Allan F.
• Primary Examiner(s): Oechsle, Anton O.
• Application Number:
  US05/048,853
• Time in Patent Office: 473 Days
• Field of Search: 128/2.5R,2.6R,2.6A,2.08,2.1R 340/279,309.1
• US Class Current: 600/536
• CPC Class Codes: A61B 5/0809 by impedance pneumography

Abstract

A respiration monitoring system utilizing an impedance pneumograph which provides an electrical signal having a characteristic that varies in accordance with transthoracic impedance changes during respiratory cycles. Motion artifacts and heart-coupled pulmonary blood flow signal components are eliminated by a narrow band-pass filter and amplifier in conjunction with an adjustable level detector which generates both respiratory rate and volume information in digital form to drive an integrating tachometer and an audiovisual alarm system having an adjustable alarm timer and an adaptive timer adapted to override the adjustable timer under certain conditions of respiration activity. Also, drifts in the total transthoracic impedance are monitored through the same alarm system to determine an equipment failure or loose electrode in the impedance pneumograph. The adjustable level detector discriminates against signals which do not exceed a first level related to respiratory inspiration after having dropped below a second level related to respiratory exhalation.

Claims

1. A physiological monitoring system comprising:

means for monitoring physiological activity in a living body and producing a correspondingly varying electrical signal;

means coupled to said first means for digitally identifying signal components corresponding to specific physiological activity;

said digital identifying means including a detector for providing output signals responsive to a characteristic of the electrical signal passing a threshold level; and

, an alarm system coupled to said digital identifying means and including an adjustable alarm timer sensitive to the time intervals between said output signals for activating an alarm under predetermined conditions of apnea, and an adaptive timing means for inhibiting the effect of selected digital output signals on the adjustable alarm timer, said predetermined conditions being determined at least in part by the setting of the adjustable alarm timer and in part by action of said adaptive timing means.

2. The physiological monitoring system of claim 1, wherein the identifying means further includes means for discriminating against signal components having a frequency outside the primary frequency range of the specific physiological activity, and means for adjustably setting the threshold value of the detector so as to discriminate against signal components having amplitudes lower than the primary amplitude of signal components resulting from the specific physiological activity.

3. The physiological monitoring system of claim 1 wherein the detector includes means for alternately detecting the signal exceeding a first threshold value and falling below a second threshold value, the second threshold value being substantially less than the first.

4. The physiological monitoring system of claim 1 further comprising measuring means for sensing the detector output signals and indicating the rate of the specific physiological activity.

5. A respiration monitor comprising:

transducer means for providing an electrical signal having characteristics which vary as a function of the respiration activity in a living body;

a breath identification circuit, including both frequency- and amplitude-discriminating means, connected to said transducer, for identifying signal components resulting from respiration and producing a digital output signal for each breath;

means connected to said breath identification circuit for monitoring the digital output signals, said means comprising an alarm means, an adjustable timer connected to said alarm means for activating said alarm means after lapse of a first time interval determined by said adjustable timer unless said adjustable timer is reset during the first time interval; and

, adaptive timing means responsive to the digital output signals for automatically resetting said adjustable timer to initiate the first time interval when the interval between successive digital output signals occurring in said first time interval is less than a second time interval determined by said adaptive timing means, the second time interval being less than the first time interval.

6. The respiration monitor of claim 5 wherein the monitoring means further comprises an integrating tachometer and a meter driven by the tachometer so as to indicate respiration rate on an average rate basis, while allowing alarms to be established on the basis of the time elapsed from the last event.

7. The apparatus of claim 5 wherein the alarm means is audiovisual, including both a lamp and an audio alarm.

8. The apparatus of claim 7 wherein the alarm means includes means for altering the audio alarm in response to the elapse of a set time interval following the activation of the alarm means.

9. The apparatus of claim 5 wherein the adaptive timing means comprises a counter, the adjustable timer being responsive to one stage of the counter.

10. The apparatus of claim 9 wherein the adaptive timing means includes an adaptive timer responsive to the digital output signals for controlling the counter to prevent the resetting of the adjustable timer when the signals occur at less than a predetermined rate on a breath-by-breath basis.

11. The respiration monitor of claim 5 wherein the frequency-discriminating means comprises a band-pass filter for substantially passing only frequencies of the transducer electrical signal which are a function of respiration.

12. The respiration monitor of claim 5 wherein the frequency-discriminating means comprises a narrow band-pass filter having a band-pass range of within about 0.2 to 2 Hz.

13. The respiration monitor of claim 5 wherein the monitoring means further comprises a lamp responsive to the digital output signals for visually identifying breath on a breath-by-breath basis.

14. The respiration monitor of claim 5 wherein the amplitude-discriminating means comprises an adjustable level detector, so that in conjunction with itS setting the digital signals provide minimum respiratory volume and flow as well as respiratory rate information.

15. The apparatus of claim 14, wherein the level detector comprises:

a first circuit for sensing the electrical signal level of the inspiratory portion of the respiratory signal component; and

, a second circuit for sensing the electrical signal level of the expiratory portion of the respiratory signal component.

16. The apparatus of claim 14 wherein the level detector drives a constant width pulse generator to provide the digital output signals from the breath identification circuit.

17. A respiration monitor comprising an impedance pneumograph for monitoring the respiration in a living body and producing an electrical signal having characteristics which vary as a function of respiration activity in the living body being monitored;

a breath identification circuit, including both frequency- and amplitude-discriminating means, connected to said impedance pneumograph, for identifying electrical signal components resulting from respiration and producing a digital output signal for each breath; and

, means for sensing the digital output signals comprising an alarm system including an adjustable alarm timer sensitive to the time intervals between the digital output signals for activating an alarm under predetermined conditions of respiration activity, and an adaptive timing means for inhibiting the effect of selected digital signals on the adjustable alarm timer, said predetermined conditions being determined at least in part by the setting of the adjustable alarm timer and in part by action of said adaptive timing means.

18. The respiration monitor of claim 17 wherein the sensing means further comprises an integrating tachometer and a meter driven by the tachometer so as to indicate respiration rate on an average rate basis, while allowing alarms to be established on the basis of the time elapsed from the last event.

19. The apparatus of claim 17 wherein the alarm system further includes an audio alarm and means for altering the audio alarm in response to the elapse of a set time interval following the onset of the alarm condition.

20. The apparatus of claim 17 wherein the adaptive timing means comprises a counter, the adjustable alarm timer being responsive to the output of said counter.

21. The apparatus of claim 17 wherein the adaptive timing means includes an adaptive timer responsive to the digital output signals for controlling the adaptive timing means to inhibit the effect of the digital output signals on the adjustable alarm timer when the signals occur at less than a predetermined rate on a breath-by-breath basis.

22. The respiration monitor of claim 17 wherein the frequency-discriminating means comprises a band-pass filter for substantially passing only frequencies of the impedance pneumograph electrical signal which are a function of respiration.

23. The respiration monitor of claim 17 wherein the frequency-discriminating means comprises a narrow band-pass filter having a band-pass range of within about 0.2 to 2 Hz.

24. The respiration monitor of claim 17 wherein the sensing means further comprises a lamp responsive to the digital output signals for visually identifying breaths on a breath-by-breath basis.

25. The respiration monitor of claim 17 wherein the amplitude-discriminating means comprises an adjustable level detector so that, in conjunction with its setting, the digital signals provide minimum respiratory volume and flow as well as respiratory rate information.

26. The apparatus of claim 25, wherein the level detector comprises:

a first circuit for sensing the electrical signal level of the inspiratory portion of the respiratory signal component; and

, a second circuit for sensing the electrical signal level of the expiratory portion of the respiratory signal component.

27. The apparatus of claim 25 wherein the level detector drives a constant width pulse generator to proviDe the digital output signals from the breath identification circuit.

28. A physiological monitoring system comprising:

a constant-current impedance pneumograph including biological skin electrodes for monitoring transthoracic impedance in a living body and producing a correspondingly varying electrical signal;

means including a band-pass filter coupled to said impedance pneumograph for detecting signal components resulting from respiration and for producing an output pulse of predetermined amplitude and duration for each breath of a selected minimum volume;

an alarm system including audiovisual alarms;

an adjustable timer for activating said audiovisual alarms after the lapse of a first time interval determined by said adjustable timer unless said adjustable timer is reset within said first time interval; and

, an adaptive timer means responsive to said output pulses for automatically resetting the adjustable timer to initiate the first time interval when the time interval between successive output pulses occurring during the first time interval is less than a second time interval determined by said adaptive timer means, said second time interval being less than said first time interval.

29. A respiration monitoring system, comprising:

transducer means for producing a first electrical signal which varies as a function of the respiration activity in a living subject;

a breath identification circuit connected to said transducer means for producing a second electrical signal in response to at least one selected respiratory characteristic of the first electrical signal; and

, means for monitoring the second electrical signal for a first selected condition of respiratory activity and providing an alarm indication in the event of the balance of said first selected condition, said means including an adaptive timing means responsive to the second electrical signal for automatically permitting said monitoring means to provide said alarm indication despite the occurrence of said first selected condition unless a second selected condition of respiratory activity is also present.

30. A respiration monitoring system as defined in claim 29 wherein said monitoring means includes an adjustable timer responsive to said adaptive timing means for providing said alarm indication under the first and second selected conditions of respiration activity determined by the adjustable timer and by the adaptive timing means, respectively.

31. A respiration monitoring system as defined in claim 29 wherein said adaptive timing means comprises:

an inhibit gate having input, output and control terminals, the output terminal of which is connected to the adjustable timer;

a counter having input, reset and output terminals, said counter providing a signal at its output terminal in response to a count of a predetermined number of selected events of the second electrical signal applied to the counter input terminal, the output terminal of said counter being connected to the input terminal of the inhibit gate, through which gate the counter output signal is passed to reset the adjustable timer; and

, an adaptive timer having input and output terminals, said adaptive timer being responsive to the second electrical signal applied to its input terminal, the output terminal of said adaptive timer being connected to the inhibit gate control terminal and the counter reset terminal to inhibit the gate and reset the counter under second selected conditions of respiration activity.

32. A respiration monitoring system as defined in claim 29 wherein said breath identification circuit comprises adjustable amplitude-discriminating means for providing said second electrical signal only when said first electrical signal exceeds a selected magnitude.

33. A respiratory monitoring system as defined in claim 32 wherein the amplitude-discriminating means provides said second electrical signal only when said first electrical signal magnitude exceeds a first selectEd level related to respiratory inspiration after falling below a second selected level related to respiratory expiration.

34. A respiration monitoring system as defined in claim 29 wherein said breath identification circuit comprises a frequency-discriminating means for substantially passing only the frequencies of the first electrical signal which are a function of respiration.

35. A respiration monitoring system as defined in claim 32 wherein said breath identification circuit further comprises frequency-discriminating means for substantially passing only the frequencies of the first electrical signal which are a function of respiration.

36. A respiration monitoring system as defined in claim 33 wherein said breath identification circuit further comprises frequency-discriminating means for substantially passing only the frequencies of the first electrical signal which are a function of respiration.

37. A respiration monitoring system comprising:

transducer means for producing a first electrical signal which varies as a function of the respiration activity in a living subject;

a breath identification circuit, including amplitude discriminating means, connected to said transducer means for producing a second electrical signal only when the first electrical signal amplitude exceeds a first selected level related to respiratory inspiration after having dropped below a second selected level related to respiratory expiration; and

, means connected to said breath identification circuit for monitoring the second electrical signal for selected conditions associated with the respiration activity.

38. The respiration monitoring system as defined in claim 37 wherein said breath identification circuit further includes frequency-discriminating means for passing substantially all the frequencies of the first electrical signal which are solely a function of respiration.

39. The respiration monitoring system as defined in claim 37 wherein said monitoring means includes an adjustable timer responsive to first selected characteristics of the second electrical signal for activating an alarm system.

40. The respiration monitoring system as defined in claim 39 wherein said means for monitoring further includes an adaptive timing means for altering the response of the adjustable timer to the second electrical signal as a function of second selected characteristics of the second electrical signal.

41. The respiration monitoring system as defined in claim 40 wherein said adaptive timing means comprises:

an inhibit gate connected to the input of said adjustable timer for preventing the resetting of the adjustable timer when the second selected characteristics of the second electrical signal are present;

a counter, connected to one input of the inhibit gate for counting a predetermined number of respiratory events present in the second electrical signal and producing a pulse in response thereto to reset the adjustable timer when the inhibit gate is open; and

, an adaptive timer having an output connected to a second input of the inhibit gate and to the counter, said adaptive timer being responsive to the second selected characteristics of the second electrical signal for closing the inhibit gate and resetting the counter.

42. A physiological monitoring system for monitoring the respiration of a living subject comprising:

transducer means for providing an electrical signal having characteristics which vary as function of the respiration of the subject being monitored;

a bilevel amplitude detector means connected to said transducer means for providing an output signal each time the electrical signal magnitude exceeds a first threshold level after having dropped below a second threshold level, the first and second levels being determined respectively by the inspiratory and expiratory portions of the electrical signal produced as a function of respiration; and

means connected to said detector for continuously monitoring the output sigNal from said detector for selected respiration characteristics including means for indicating the absence of said selected respiratory characteristics.

43. In a physiological monitoring system of the type used to monitor respiration, wherein a transducer converts the physiological activity associated with respiration into an electrical signal and wherein a breath identification circuit detects that portion of the electrical signal associated with respiration activity, an adaptive alarm system comprising:

an adjustable timer for producing an alarm when the time interval between breaths exceeds a first selected time interval; and

, adaptive timing means responsive to each breath and connected to the adjustable timer for automatically resetting said adjustable timer to initiate the first time interval when the time interval between successive breaths is less than a second time interval determined by said adaptive timing means, the second time interval being less than the first time interval.