Physiological occurrence, such as apnea, monitor and X-ray triggering device

• US 4,289,142 A
• Filed: 11/24/1978
• Issued: 09/15/1981
• Est. Priority Date: 11/24/1978
• Status: Expired due to Term

• Current Assignee: Kenneth L. Kearns
• Original Assignee: Kenneth L. Kearns
• Inventors: Kearns, Kenneth L.
• Primary Examiner(s): Kamm, William E.
• Application Number:
  US05/963,352
• Time in Patent Office: 1,026 Days
• Field of Search: 128/695, 128/696, 128/700, 128/702, 128/706, 128/709, 128/710, 128/716, 128/721, 128/722, 128/723, 128/724
• US Class Current: 600/529
• CPC Class Codes: A61B 5/02455 provided with high/low alarm devices
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• 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 6/541 involving acquisition triggered by a physiological signal

Abstract

A respiration monitor and X-ray trigger apparatus wherein signals are generated indicative of respiration rate, respiration extrema, and heart rate. A trigger signal is selectively generated to the X-ray machine just prior to occurrence of a selected respiration extrema. The value of the respiration signal at a sample occuring just after detection of the selected extrema is stored, and modified in accordance with the resolution of the system. The X-ray trigger signal is generated, if not otherwise inhibited, upon detection of the next occurrence of the modified value in the respiration wave form. Apnea alarms are generated if a predetermined decrease in respiration rate is detected in successive periods in conjunction with a predetermined number of decelerating heart beats. An alarm is also generated if the respiration rate and heart rate signals appear to indicate that the respiration and heart rates are equal for a predetermined number of periods, or if the respiration or heart rates stray outside of preset threshold values. Provisions are included for adaptive DC offset, and to eliminate electromagnetic interference. Amplitude, time domain, and slew rate discrimination against artifacts are also provided.

Claims

1. An apnea monitor comprising:

means, for generating a respiration rate signal indicative of the rate of respiration;

means, for generating a heart rate signal indicative of the rate of heart beats; and

means, responsive to said respiration rate signal and said heart rate signal, for generating an apnea alarm signal when the respiration rate decreases by a predetermined amount in successive periods, and said heart rate decreases in a predetermined number of successive periods.

2. The respiration monitor of claim 1 wherein said predetermined amount is one-half (1/2) and said predetermined number is four (4).

3. The apnea monitor of claims 1 or 2 further including means, responsive to said respiration rate signal and said heart rate signal, for generating an alarm when the respiration rate signal and heart rate signal appear to indicate that respiration rate and heart rate are equal over a predetermined number of periods.

4. The respiration monitor of claim 3 further including means, responsive to said respiration rate signal, for generating an alarm signal when the respiration rate exceeds a predetermined high threshold level.

5. The respiration monitor of claim 3 further including means, responsive to said respiration rate signal, for generating an alarm signal when the respiration rate falls below a predetermined low threshold level.

6. The apnea monitor of claim 3 further including:

means for generating a valid time signal indicative of valid time periods during which said apnea monitor is providing valid signals indicative of heart rate and respiration rate; and

means, responsive to said valid time signal and said alarm signals, for counting the number of times said alarm signal is generated during a predetermined period of said valid time.

7. The respiration monitor of claim 3 wherein said means for generating a heart rate signal comprises:

means for generating an ECG signal;

means for generating QRS pulses indicative of the occurrence of QRS complexes in said ECG signal; and

means, responsive to said QRS pulses for generating a heart rate count indicative of said heart rate.

8. The respiration monitor of claim 7 wherein said means for generating a heart rate signal further includes:

heart rate artifact rejection means, responsive to said heart rate count, for generating a valid heart rate count signal when an instantaneous heart rate count differs from a base heart rate count by less than a predetermined rate threshold in accordance with a maximum physiological change in heart rate per unit time of said subject;

said base heart rate count being the last previous heart rate count which differed from the previous base heart rate count by less than said predetermined rate threshold; and

output means, responsive to said heart rate count and said valid heart rate count signal, for selectively providing indicia of said heart rate.

9. The apnea monitor of claim 3 comprising means for generating an analog signal including electrodes disposed on said subject;

a conductive shielding enclosing said apnea monitor to reduce effects of electromagnetic interference;

means, for developing a signal indicative of common mode signals between said electrodes;

means for inverting said common mode signal and applying said inverted signal to a feedback signal to said means for generating an analog signal; and

means for applying said inverted signal to said shielding structure whereby said electromagnetic interference is substantially eliminated.

10. The respiration monitor of claims 1 or 2 further including means, responsive to said respiration rate signal, for generating an alarm signal when the respiration rate exceeds a predetermined high threshold level.

11. The respiration monitor of claim 10 further including means, responsive to said respiration rate signal, for generating an alarm signal when the respiration rate falls below a predetermined low threshold level.

12. The respiration monitor of claims 1 or 2 further including means, responsive to said respiration rate signal, for generating an alarm signal when the respiration rate falls below a predetermined low threshold level.

13. The respiration monitor of claim 1 wherein said means for generating a respiration rate signal comprises:

means for generating a slope reversal signal indicative of reversals in slope in said analog respiration signal;

means, responsive to said slope reversal signal, for generating a rate count indicative of the frequency of slope reversal in a predetermined direction;

artifact rejection means, responsive to said rate count, for determining if said rate count is within allowable limits from a base count, and generating a valid count signal indicative of said determination;

said base count being the last preceding rate count within said allowable limits from the preceding base count, said allowable limits being in accordance with the physiological respiration of said subject; and

output means, responsive to said rate count and said valid count signal, for selectively providing indicia of respiration rate.

14. The respiration monitor of claim 13 wherein said artifact rejection means comprises:

first means, for temporarily storing the instantaneous rate count;

second means, cooperating with said first storage means, for, in response to said valid count signal, selectively storing the contents of said first storage means as said base count;

means, responsive to said rate count, for generating rate difference magnitude and rate difference sign signals respectively, indicative of the magnitude and sign of the rate difference between said instantaneous rate count and said base count;

means for generating a signal indicative of said allowable limits;

comparator means, responsive to said rate difference magnitude signal and said signal indicative of said allowable limits for generating output signals respectively indicative of the rate difference magnitude being greater than said allowable limits or within said allowable limits;

means, responsive to said valid count signal and a signal indicative of the generation of a rate count, for generating a force signal if a predetermined number of rate counts are generated not within said allowable limits; and

logic means, responsive to said force signal, said comparator means output signals, and said rate difference sign signal for generating said valid count signal if said instantaneous rate count is within said allowable limits and in response to said force signal.

15. The respiration monitor of claims 13 or 14 further including means, responsive to said respiration rate signal and said heart rate signal, for generating an alarm when the respiration rate signal and heart rate signal appear to indicate that respiration rate and heart rate are equal over a predetermined number of periods.

16. The respiration monitor of claims 13 or 14 further including means, responsive to said respiration rate signal, for generating an alarm signal when the respiration rate exceeds a predetermined high threshold level.

17. The respiration monitor of claims 13 or 14 further including means, responsive to said respiration rate signal, for generating an alarm signal when the respiration rate falls below a predetermined low threshold level.

18. The respiration monitor of claims 13 or 14 further including means, responsive to said respiration rate signal, for generating indicia of the respiration rate being outside of predetermined bounds.

19. The respiration monitor of claim 18 wherein said predetermined amount is one-half (1/2) and said predetermined number is four (4).

20. The respiration monitor of claim 18 wherein said means for generating an analog signal comprises means, including electrodes disposed on said subject, for generating a signal indicative of transthoracic impedance, said transthoracic impedance signal being said analog signal indicative of the respiration cycle of said subject, and wherein said respiration monitor further comprises:

means for comparing said transthoracic impedance signals to a plurality of predetermined values, and generating comparison signals indicative of said comparisons, said predetermined values being established respective ranges of impedances; and

display means, responsive to said comparison signals, for providing indicia of the range of impedance into which said transthoracic impedance falls, whereby the quality of the electrode connections to said subject may be determined.

21. The respiration monitor of claim 20 further including means for generating an alarm in response to said transthoracic impedance being outside of a range defined by respective high and low predetermined values in accordance with physiological maximum and minimum of thoracic impedance.

22. The respiration monitor of claims 13 or 14 wherein said predetermined amount is one-half (1/2) and said predetermined number is four (4).

23. The respiration monitor of claims 13 or 14 wherein said means for generating an analog signal comprises means, including electrodes disposed on said subject, for generating a signal indicative of transthoracic impedance, said transthoracic impedance signal being said analog signal indicative of the respiration cycle of said subject, and wherein said respiration monitor further comprises:

means, for comparing said transthoracic impedance signals to a plurality of predetermined values, and generating comparison signals indicative of said comparisons, said predetermined values being established respective ranges of impedances; and

display means, responsive to said comparison signals, for providing indicia of the range of impedance into which said transthoracic impedance falls, whereby the quality of the electrode connections to said subject may be determined.

24. The respiration monitor of claim 23 further including means for generating an alarm in response to said transthoracic impedance being outside of a range defined by respective high and low predetermined values in accordance with physiological maximum and minimum of thoracic impedance.

25. The respiration monitor of claim 1 wherein said means for generating a heart rate signal comprises:

means for generating an ECG signal;

means for generating QRS pulses indicative of the occurrence of QRS complexes in said ECG signal; and

means, responsive to said QRS pulses for generating a heart rate count indicative of said heart rate.

26. The respiration monitor of claim 25 wherein said means for generating a heart rate signal further includes:

heart rate artifact rejection means, responsive to said heart rate count, for generating a valid heart rate count signal when an instantaneous heart rate count differs from a base heart rate count by less than a predetermined rate threshold in accordance with a maximum physiological change in heart rate per unit time of said subject;

said base heart rate count being the last previous heart rate count which differed from the previous base heart rate count by less than said predetermined rate threshold; and

output means, responsive to said heart rate count and said valid heart rate count signal, for selectively providing indicia of said heart rate.

35. The apnea monitor of claims 1 or 27 further including:

means for generating a valid time signal indicative of valid time period during which said apnea monitor is providing valid signals indicative of heart rate and respiration rate; and

means, responsive to said valid time signal and said alarm signals, for counting the number of times said alarm signal is generated during a predetermined period of said valid time.

36. The apnea monitor of claims 1 or 27 comprising means for generating an analog signal including electrodes disposed on said subject;

a conductive shielding enclosing said apnea monitor to reduce effects of electromagnetic interference;

means, for developing a signal indicative of common mode signals between said electrodes;

means for inverting said common mode signal and applying said inverted signal to a feedback signal to said means for generating an analog signal; and

means for applying said inverted signal to said shielding structure whereby said electromagnetic interference is substantially eliminated.

94. The respiration monitor of claims 8, 84, 92 or 93 wherein said means for generating an analog signal includes electrodes disposed on said subject, and said respiration monitor is disposed within a conductive shielding to reduce effects of electromagnetic interference, further including:

means, for developing a signal indicative of common mode signals between said electrodes;

means for inverting sid common mode signal and applying said inverted signal to a feedback signal to said means for generating an analog signal; and

means for applying said inverted signal to said shielding structure whereby said electromagnetic interference is substantially eliminated.

95. The respiration monitor of claims 1, 27, 37, 81 84 or 92 wherein said means for generating an respiration signal comprises:

current source means, for generating an on-off modulated constant current signal;

electrodes, electrically coupled to said current source means for passing said on-off modulated constant current signal through said body;

a high input impedance differential amplifier, DC coupled to said electrodes, for developing a modulated impedance signal having an AC component indicative of the change in the transthoracic impedance of the subject;

a phase synchronous demodulator, responsive to said modulated impedance signal and a signal indicative of said on-off modulated constant current signal, for generating a demodulated impedance signal indicative of the transthoracic impedance of said subject and including said AC component; and

first low pass filter means, having substantially flat frequency response with respect to the frequency range of said AC component and responsive to said demodulated impedance signal for generating said analog respiration signal.

96. The respiration monitor of claim 95 wherein said means for generating an analog signal comprises means for generating an impedance signal indicative of the transthoracic impedance of the subject and said predetermined value corresponds to approximately 0.3 ohms.

27. A respiration monitor comprising:

means for generating a respiration rate signal indicative of the rate of respiration;

artifact rejection means, responsive to said respiration rate signal, for inhibiting changes in said respiration rate signal not in accordance with physiological respiration;

means, for generating a heart rate signal indicative of the rate of heart beats; and

means, responsive to said respiration rate signal as operated upon said artifact rejection means, and said heart rate signal, for generating an alarm when the respiration rate signal and heart rate signal indicate that respiration rate and heart rate are equal over a predetermined number of periods, indicating erroneous detection of heart signals as respiration signals.

28. The respiration monitor of claim 27 further including means, responsive to said respiration rate signal, for generating an alarm signal when the respiration rate exceeds a predetermined high threshold level.

29. The respiration monitor of claims 27 or 28 further including means, responsive to said respiration rate signal, for generating an alarm signal when the respiration rate falls below a predetermined low threshold level.

30. The respiration monitor of claim 27 wherein said means for generating a respiration rate signal comprises:

means for generating a slope reversal signal, for generating a rate count indicative of the frequency slope reversal in a predetermined direction;

artifact eliminator means, responsive to said rate count, for determining if said rate count is within allowable limits from a base count, and generating a valid count signal indicative of said determination;

said base count being the last preceding rate count within said allowable limits from the preceding base count, said allowable limits being in accordance with the physiological respiration of said subject; and

output means, responsive to said rate count and said valid count signal, for selectively providing indicia of respiration rate.

31. The respiration monitor of claim 30 wherein said artifact eliminator means comprises:

first means, for temporarily storing the instantaneous rate count;

second means, cooperating with said first storage means, for, in response to said valid count signal, selectively storing the contents of said first storage means as said base count;

means, responsive to said rate count, for generating rate difference magnitude and rate difference sign signals respectively, indicative of the magnitude and sign of the rate difference between said instantaneous rate count and said base count;

means for generating a signal indicative of said allowable limits;

comparator means, responsive to said rate difference magnitude signal and said signal indicative of said allowable limits for generating output signals respectively, indicative of the rate difference magnitude being greater than said allowable limits or within said allowable limits;

means, responsive to said valid count signal and said signal indicative of the generation of a rate count, for generating a force signal if a predetermined number of rate counts are generated not within said allowable limits; and

logic means, responsive to said force signal, said comparator means output signal, and said rate difference sign signal, for generating said valid count signal if said instantaneous rate count is within said allowable limits and in response to said force signal.

32. The respiration monitor of claims 30 or 31 further including means, responsive to said respiration rate signal, for generating an alarm signal when the respiration rate exceeds a predetermined high threshold level.

33. The respiration monitor of claims 30 or 31 further including means, responsive to said respiraton rate signal, for generating an alarm signal when the respiration rate falls below a predetermined low threshold level.

34. The respiration monitor of claims 30 or 31 further including means, responsive to said respiration rate signal, for generating indicia of the respiration rate being outside of predetermined bounds.

37. A respiration monitor comprising:

means for generating an analog respiration signal directly reprsentative of the respiration of a subject;

means, responsive to said analog respiration signal, for periodically sampling said analog respiration signal and generating sample signals indicative of said samples;

amplitude discriminator means, responsive to said sample signal, for generating a signal indicative of the difference between the instantaneous sample and a mean sample, and mean sample being the last preceding sample differing from the preceding means sample by a predetermined value;

means, cooperating with said amplitude discriminator means, for generating a sign signal indicative of the sign of said difference;

means, responsive to said sign signal, for generating indicia of a sample value in accordance with the sample associated with a predetermined change in the sign of said difference; and

means for generating an extrema signal upon next occurrence of a sample having said sample value.

38. The respiration monitor of claim 37 further including time domain discriminator means, responsive to said sign signal, for inhibiting generation of said indicia of said sample value of the sample associated with a particular predetermined change in sign, if said particular predetermined change in sign occurs within a first predetermined prescribed time period after the just preceding predetermined change in sign, said first prescribed time period being associated with the rate parameter of the physiological respiration of the subject.

39. The respiration monitor of claim 37 further including time domain discriminator means, responsive to said sign signal, for inhibiting generation of said indicia of said sample value of the sample associated with a particular predetermined change in sign, if said particular predetermined change in sign occurs within a first prescribed time period after a preceding change in sign in the opposite direction from said predetermined change in sign, said first prescribed time period being associated with the inspiratory to expiratory ratio of the physiological respiration of the subject.

40. The respiration monitor of claim 37 further including time domain discriminator means, responsive to said sign signal, for inhibiting generation of said indicia of said sample value of the sample associated with a particular predetermined change in sign, if said particular predetermined change in sign occurs within a first prescribed time period after the just preceding determined change in sign, said first predetermined prescribed time period being associated with the rate parameter of the physiological respiraton of the subject, and for inhibiting generation of said indicia of said sample value if said particular predetermined change in sign occurs within a second prescribed time period after a preceding change in sign in the opposite direction from said predetermined sign change, said second prescribed time period being associated with the inspiratory to expiratory ratio of the physiological rspiration of the subject.

41. The respiration monitor of claim 37 further including time domain discriminator means, responsive to said sign signal, for inhibiting generation of an extrema signal associated with a particular predetermined change in sign, if said particular predetermined change in sign occurs within a first prescribed time period after the just preceding predetermined change in signa, said first prescribed time period being associated with the rate parameter of the physiological respiration of the subject.

42. The respiration monitor of claim 37 further including time domain discriminator means, responsive to said sign signal, for inhibiting generation of an extrema signal associated with a particular predetermined change in sign, if said particular predetermined change in sign occurs within a first prescribed time period after the just preceding predetermined change in sign, said first prescribed time period being associated with the rate parameter of the physiological respiration of the subject.

43. The respiration monitor of claims 39 or 42 wherein said predetermined change in sign is from positive to negative and said first prescribed time period is approximately 111 msec.

44. The respiration monitor of claims 39 or 42 wherein said predetermined change in sign is from negative to positive and said prescribed time period is approximately 222 msec.

45. The respiration monitor of claim 37 further including time domain discriminator means, responsive to said sign signal, for inhibiting generation of an extrema signal associated with a particular predetermined change in sign, if said particular predetermined change in sign occurs within a first prescribed time period after the just preceding predetermined change in sign, said first prescribed time period being associated with the rate parameter of the physological respiration of the subject, and for inhibiting generation of said indicia of said sample value if said particular predetermined change in sign occurs within a second prescribed time period after a preceding change in sign in the opposite direction from said predetermined sign change, said second prescribed time period being associated with the inspiratory to expiratory ratio of the physiological respiration of the subject.

46. The respiration monitor of claim 38, 40, 41 or 45 wherein said first prescribed time period is approximately 333 msec.

47. The respiration monitor of claim 46 wherein said predetermined change in sign is from positive to negative and said second prescribed time period is approximately 111 msec.

48. The respiration monitor of claim 46 wherein said predetermined change in sign is from negative to positive and said second prescribed time period is approximately 222 msec.

49. The respiration monitor of claims 40 or 45 wherein said predetermined change in sign is from positive to negative and said second prescribed time period is approximately 111 msec.

50. The respiration monitor of claims 40 or 45 wherein said predetermined change in sign is from negative to positive and said second prescribed time period is approximately 222 msec.

51. The respiration monitor of claims 37, 38, 39, 40, 41 or 45 further including:

means, responsive to said sign signal, for generating a rate count indicative of the frequency of sign changes in a predetermined direction;

artifact rejection means, responsive to said rate count, for determining if said rate count is within allowable limits from a base count, and generating a valid count signal indicative of said determination;

said base count being the last preceding rate count within said allowable limits from the preceding base count, said allowable limits being in accordance with the physiological respiration of said subject; and

output means, responsive to said rate count and said valid count signal, for selectively providing indicia of respiration rate.

52. The respiration monitor of claim 51 wherein said artifact rejection means comprises:

first means, for temporarily storing the instantaneous rate count;

second means, cooperating with said first storage means, for, in response to said valid count signal, selectively storing the contents of said first storage means as said base count;

means, responsive to said rate count, for generating rate difference magnitude and rate difference sign signals, respectively indicative of the magnitude and sign of the rate difference between said instantaneous rate count and said base count;

means for generating a signal indicative of said allowable limits;

comparator means, responsive to said rate difference magnitude signal and said signal indicative of said allowable limits for generating respective output signals indicative of the rate difference magnitude being greater than said allowable limits or within said allowable limits;

means, responsive to said valid count signal and a signal indicative of the generation of a rate count, for generating a force signal if a predetermined number of rate counts are generated not within said allowable limits; and

logic means, responsive to said force signal, said comparator means output signal, and said rate difference sign signal for generating said valid count signal if said instantaneous rate count is within said allowable limits and for generating said valid count signal in response to said force signal.

53. The respiration monitor of claim 52 wherein said output means comprises:

resettable means, responsive to said comparator means output signals, said signal indicative of the sign of said rate difference and said rate count, for selectively generating an average rate count representative of a predetermined fraction of said rate counts over a predetermined number of breaths, said resettable means including means to effect resetting and reinitialization of generation of said average rate count in response to generation of a rate count not with said allowable limits.

54. The respiration monitor of claim 53 further including means, responsive to said average rate count, for generating an alarm if said average rate count exceeds a preset threshold value.

55. The respiration monitor of claim 53 further including means, responsive to said average rate count, for generating an alarm if said average rate count falls below a preset threshold value.

56. The respiration monitor of claim 53 further including means, responsive to said average rate count, for generating an alarm if said average rate count is not within predetermined threshold limits.

57. The respiration monitor of claim 52 wherein said means for generating an analog signal comprises means for generating an impedance signal indicative of the transthoracic impedance of said subject, and said predetermined value corresponds to approximately 0.3 ohms.

58. The respiration monitor of claim 51 wherein said output means comprises:

means, responsive to said rate count, for selectively providing display of said respiration rate as averaged over a predetermined number of breaths.

59. The respiration monitor of claim 51 wherein said means for generating an analog signal comprises means, including electrodes disposed on said subject, for generating a signal indicative of transthoracic impedance, said transthoracic impedance signal being said analog signal indicative of the respiration cycle of said subject, and wherein said respiration monitor further comprises:

means, for comparing said transthoracic impedance signals to a plurality of predetermined values, and generating comparison signals indicative of said comparisons, said predetermined values being established respective ranges of impedances; and

display means, responsive to said comparison signals, for providing indicia of the range of impedance into which said transthoracic impedance falls, whereby the quality of the electrode connections to said subject may be determined.

60. The respiration monitor of claim 50 further including means for generating an alarm in response to said transthoracic impedance being outside of a range defined by respective high and low predetermined values in accordance with physiological maximum and minimum of thoracic impedance.

61. The respiration monitor of claim 51 wherein said means for generating an analog signal comprises means for generating an impedance signal indicative of the transthoracic impedance of said subject, and said predetermined value corresponds to approximately 0.3 ohms.

62. The respiration monitor of claims 37, 40 or 45 wherein said means for generating an analog signal comprises means for generating an impedance signal indicative of the transthoracic impedance of the subject and said predetermined value corresponds to approximately 0.3 ohms.

63. The respiration monitor of claim 37 wherein said means for generating an analog signal includes electrodes disposed on said subject, and said respiration monitor is disposed within a conductive shielding to reduce effects of electromagnetic interference, and said respiration monitor further includes:

means, for developing a signal indicative of common mode signals between said electrodes;

means for inverting said common mode signal and applying said inverted signal to a feedback signal to said means for generating said analog respiration signal; and

means for applying said inverted signal to said shielding structure whereby said electromagnetic interference is substantially eliminated.

79. The respiration monitor of claim 43 wherein said means for generating an analog signal comprises means, including electrodes disposed on said subject, for generating a signal indicative of transthoracic impedance, said transthoracic impedance signal being said analog signal indicative of the respiration cycle of said subject, and wherein said respiration monitor further comprises:

means, for comparing said transthoracic impedance signals to a plurality of predetermined values, and generating comparison signals indicative of said comparisons, said predetermined values being established respective ranges of impedances; and

display means, responsive to said comparison signals, for providing indicia of the range of impedance into which said transthoracic impedance falls, whereby the quality of the electrode connections to said subject may be determined.

80. The respiration monitor of claim 79 further including means for generating an alarm in response to said transthoracic impedance being outside of a range defined by respective high and low predetermined values in accordance with physiological maximum and minimum of thoracic impedance.

64. A respiration monitor comprising:

means for generating an analog respiration signal having a waveform directly representative of the respiration of a subject;

means, responsive to said analog respiration signal, for detecting reversals in the slope of said waveform and generating a slope reversal signal indicative of the occurrence of a slope reversal in said analog respiration signal waveform;

means, responsive to said slope reversal signal, for storing a stored value indicative of said analog respiration signal waveform at said detected slope reversal;

means, cooperating with said means for generating said slope reversal signal, for generating a valid sample signal if the excursion of the slope reversal from said stored value exceeds a predetermined threshold value to ensure that said slope reversal relates to an event in physical respiration;

means, responsive to said valid sample signal, for storing indicia the value of said analog respiration signal at said threshold excursion from said reversal if said excursion exceeds said threshold value; and

means, responsive to said analog respiration signal for comparing said analog respiration signal to said stored indicia signal value at threshold excursion, and generating an actuation signal upon the next occurrence in said analog respiration signal of a value in accordance with said stored value.

65. The respiration monitor of claim 64 wherein said value in accordance with said stored value is substantially equal to said stored value offset by said threshold value.

66. The respiration monitor of claim 64 further including tachometry means, responsive to said slope reversal signal, for determining the time interval between successive predetermined ones of said slope reversal signals and generating therefrom a signal indicative of respiration rate.

67. The respiration monitor of claim 66 further including time discrimination means, responsive to said slope reversal signal, for inhibiting the operation of said tachometry means with respect to successive ones of said slope reversal signals occurring within a prescribed time period after a preceding slope reversal.

68. The respiration monitor of claims 66 or 67 wherein said tachometry means comprises:

means, responsive to said slope reversal signal, for generating a rate count indicative of the frequency of slope reversal in a predetermined direction;

artifact rejection means, responsive to said rate count, for determining if said rate count is within allowable limits from a base count, and generating a valid count signal indicative of said determination;

said base count being the last preceding rate count within said allowable limits from the preceding base count, said allowable limits being in accordance with the physiological respiration of said subject; and

output means, responsive to said rate count and said valid count signal, for selectively providing indicia of respiration rate.

69. The respiration monitor of claim 68 wherein said artifact rejection means comprises:

first means, for temporarily storing the instantaneous rate count;

second means, cooperating with said first storage means, for, in response to said valid count signal, selectively storing the contents of said first storage means as said base count;

means, responsive to said rate count, for generating rate difference magnitude and rate difference sign signals, respectively indicative of the magnitude and sign of the rate difference between said instantaneous rate count and said base count;

means for generating a signal indicative of said allowable limits;

comparator means, responsive to said rate difference magnitude signal and said signal indicative of said allowable limits, for generating output signals respectively indicative of the rate difference magnitude being greater than said allowable limits, or within said allowable limits;

means, responsive to said valid count signal and a signal indicative of the generation of a rate count, for generating a force signal if a predetermined number of rate counts are generated not within said allowable limits; and

logic means, responsive to said force signal, said comparator means output signal, and said difference sign signal for generating said valid count signal if said instantaneous rate count is within said allowable limits and for generating said valid count signal in response to said force signal.

70. The respiration monitor of claim 69 wherein means for generating said signal indicative of said allowable limit comprises means for generating a signal indicative of a predetermined maximum increase in heart rate in accordance with the physiological respiration of the subject;

and

said logic means includes means for generating said valid count signal when said rate difference is less than said maximum increase, and means for generating said valid count signal if said rate count is decreasing with respect to said base count.

71. The respiration monitor of claim 69 wherein said output means comprises:

means, responsive to said rate count, for selectively providing display of said respiration rate as averaged over a predetermined number of breaths.

72. The respiration monitor of claim 69 wherein said output means comprises:

resettable means, responsive to said comparator means output signals, said signal indicative of the sign of said rate difference and said rate count, for selectively generating an average rate count representative of a predetermined fraction of said rate counts over a predetermined number of breaths, said resettable means including means for effecting reinitialization of generation of said average rate count in response to generation of a rate count not within said allowable limits.

73. The respiration monitor of claim 72 further including means, responsive to said average rate count, for generating an alarm if said average rate count exceeds a preset threshold value.

74. The respiration monitor of claim 73 further including means, responsive to said average rate count, for generating an alarm if said average rate count falls below a preset threshold value.

75. The respiration monitor of claim 73 further including means, responsive to said average rate count, for generating an alarm if said average rate count is not within predetermined threshold limits.

76. The respiration monitor of claim 72 wherein said means for generating an analog signal comprises means, including electrodes disposed on said subject, for generating a signal indicative of transthoracic impedance, said transthoracic impedance signal being said analog signal indicative of the respiration cycle of said subject, and wherein said respiration monitor further comprises:

means, for comparing said transthoracic impedance signals to a plurality of predetermined values, and generating comparison signals indicative of said comparisons, said predetermined values being established respective ranges of impedances; and

display means, responsive to said comparison signals, for providing indicia of the range of impedance into which said transthoracic impedance falls, whereby the quality of the electrode connections to said subject may be determined.

77. The respiration monitor of claim 76 further including means for generating an alarm in response to said transthoracic impedance being outside of a range defined by respective high and low predetermined values in accordance with physiological maximum and minimum of thoracic impedance.

78. The respiration monitor of claim 68 wherein said output means comprises:

means, responsive to said rate count, for selectively providing display of said respiration rate as averaged over a predetermined number of breaths.

101. The respiration monitor of claims 64 or 81 wherein said means for generating an analog signal comprises means, including electrodes disposed on said subject, for generating a signal indicative of transthoracic impedance, said transthoracic impedance signal being said analog signal indicative of the respiration cycle of said subject, and wherein said respiration monitor further comprises:

means for comparing said transthoracic impedance signals to a plurality of predetermined values, and generating comparison signals indicative of said comparisons, said predetermined values being established respective ranges of impedances; and

display means, responsive to said comparison signals, for providing indicia of the range of impedance into which said transthoracic impedance falls, whereby the quality of the electrode connections to said subject may be determined.

102. The respiration monitor of claim 101 further including means for generating an alarm in response to detection of a transthoracic impedance outside of a range defined by respective high and low predetermined values in accordance with physiological maximum and minimum of thoracic impedance.

81. A respiration monitor comprising:

means for generating an analog signal indicative of the respiration cycle of a subject;

means, responsive to the analog signal, for generating sequential samples representative of said analog signal;

storage means, responsive to said sequential samples and to control signals applied thereto, for selectively storing, in sequence to said control signals, indicia of a selected one of said samples as a base level sample;

means, for generating a difference signal indicative of the differences between each respective sample in sequence and said base level sample;

means for generating a threshold signal indicative of a preset threshold value;

means, responsive to said threshold signal and said difference signal, for sequentially comparing the differences associated with said respective samples to said preset threshold value and selectively generating in accordance with the comparison said control signal to said storage means to effect storage of the respective sample as said base level sample;

means for generating an offset compensated signal indicative of said base level sample subtracted from said analog signal; and

processing means for analyzing said offset compensated signal.

82. The respiration monitor of claim 81 wherein the means for generating sequential samples comprises an analog-to-digital converter.

83. The respiration monitor of claim 81 wherein said processing means comprises:

means, responsive to said offset compensated signal, for generating a slope reversal signal indicative of the occurrence of a slope reversal in said offset compensated signal, and storing the value of said offset compensated signal at said detected slope reversal;

means, cooperating with said means for generating said slope reversal signal, for generating a valid sample signal if the excursion of the slope reversal in said offset compensated signal from said stored value exceeds a predetermined threshold value, to ensure that said slope reversal relates to an event in physical respiration, means for storing indicia of the value of said offset compensated signal at said threshold excursion from said slope reversal if said excursion exceeds said threshold value; and

means, responsive to said offset compensated signal, for comparing said offset compensated signal to said stored indicia signal value at threshold excursion, and generating an actuation signal upon the next occurrence in said offset compensated signal of said stored signal value at threshold excursion, modified by a predetermined amount.

84. The respiration monitor of claim 81 wherein said processing means comprises:

means, responsive to said offset compensated signal, for periodically sampling said offset compensated signal and generating sample signals indicative of said samples;

amplitude discriminator means, responsive to said sample signal, for generating a signal indicative of the difference between the instantaneous sample and a mean sample, said mean sample being the last preceding sample differing from the preceding mean sample by a predetermined value;

means, cooperating with said amplitude discriminator means, for generating a sign signal indicative of the sign of said difference;

means, responsive to said sign signa, for generating indicia of the value of a sample associated with a predetermined change in the sign of said difference, modified by a predetermined amount; and

means for generating an extrema signal upon next occurrence of a sample having a modified value.

85. The respiration monitor of claim 84 further including:

time discriminator means, responsive to said sign signal, for inhibiting generation of said indicia of said modified value of the sample associated with a particular predetermined change in sign, if said particular predetermined change in sign occurs within a first prescribed time period after the just preceding predetermined change in sign;

said first predetermined prescribed time period being associated with the rate parameter of the physiological respiration of the subject, and for inhibiting generation of said indicia of said modified value if said particular predetermined change in sign occurs within a second prescribed time period after a preceding change in sign in the opposite direction from said predetermined sign change, said prescirbed time period being associated with the inspiratory to expiratory ratio of the physiological respiration of the subject.

86. The respiration monitor of claim 84 further including:

time discriminator means, responsive to said sign signal, for inhibiting generation of an extrema signal associated with a particular predetermined change in sign, if said particular predetermined change in sign occurs within a first prescribed time period after the just preceding predetermined change in sign;

said first prescribed time period being associated with the rate parameter of the physiological respiration of the subject, and for inhibiting generation of said indicia of said modified value if said particular predetermined change in sign occurs within a second prescribed time period after a preceding change in sign in the opposite direction from said predetermined sign change, said second prescribed time period being associated with the inspiratory to expiratory ratio of the physiological respiration of the subject.

87. The respiration monitor of claims 85 or 86 wherein said first prescribed time period is approximately 333 msec.

88. The respiration monitor of claim 87 wherein said predetermined change in sign is from positive to negative and said second prescribed time period is approximately 111 msec.

89. The respiration monitor of claim 87 wherein said predetermined change in sign is from negative to positive and said second prescribed time period is approximately 222 msec.

90. The respiration monitor of claims 85 or 86 wherein said predetermined change in sign is from positive to negative and said second prescribed time period is approximately 111 msec.

91. The respiration monitor of claims 85 or 86 wherein said predetermined change in sign is from negative to positive and said second prescribed time period is approximately 222 msec.

92. In the respiration monitor of claim 84 the further improvement wherein said processing means further includes:

means, responsive to said sign signal, for generating a rate count indicative of the frequency of sign changes in a predetermined direction;

artifact rejection means, responsive to said rate count, for determining if said rate count is within allowable limits from a base count, and generating a valid count signal indicative of said determination;

said base count being the last preceding rate count within said allowable limits from the preceding base count, said allowable limits being in accordance with the physiological respiration of said subject; and

output means, responsive to said rate count and said valid count signal, for selectively providing indicia of respiration rate.

93. The respiration monitor of claim 92 wherein said artifact rejection means comprises:

first means, for temporarily storing the instantaneous rate count;

second means, cooperating with said first storage means, in response to said valid count signal for selectively storing the contents of sid first storage means as said base count;

means, responsive to said rate count, for generating rate difference magnitude and rate difference sign signals respectively, indicative of the magnitude and sign of the rate difference between said instantaneous rate count and said base count;

means for generating a signal indicative of said allowable limits;

comparator means, repsonsive to said rate difference magnitude signal and said signal indicative of said allowable limits for generating respective output signals indicative of the rate difference magnitude being greater than said allowable limits or within said allowable limits;

means, responsive to said valid count signal and a signal indicative of the generation of a rate count, for generating a force signal if a predetermined number of rate counts are generated not within said allowable limits; and

logic means, responsive to said force signal, said comparator means output signal, and said rate difference sign signal for generating said valid count signal if said instantaneous rate count is within said allowable limits and for generating said valid count signal in response to said force signal.

97. The respiration monitor of claim 92 wherein said processing means includes:

means for generating maxima and minima signals, respectively indicative of maxima and minima in said offset compensated signal;

actuation means, responsive to at least a predetermined one of said maxima and minima signals, for generating an actuation signal in response to said predetermined one of said extrema signal;

time domain discriminator means, repsonsive to at least said predetermined one of said maxima and minima signals, for inhibiting said actuation means with respect to a particular predetermined one of said maxima and minima if said particular predetermined one of said maxima or minima occurs within a first prescribed time period from a preceding predetermined one of said maxima and minima, said first prescribed time period being associated with the rate of respiration of said subject, and for inhibiting said actuation means with respect to said particular one of said maxima or minima if said particular one occurs within a second prescribed time period of a minima or maxima of the opposite type, said second prescribed time period being associated with the inspiratory to expiratory ratio of the respiration of said subject.

98. The respiration monitor of claim 97 wherein said first prescribed time period is approximately 333 msec.

99. The respiration monitor of claims 97 or 98 wherein said predetermined one of maxima or minima is a maxima and said second prescribed time period is approximately 111 msec.

100. The respiration monitor of claims 97 or 98 wherein said predetermined one of maxima and minima and said second prescribed time period is approximately 222 msec.

103. In apparatus of the type including means for generating an analog representation of the respiration of a subject;

means, responsive to said analog representation for generating maxima and minima signals, respectively indicative of maxima and minima in said analog representation of respiration; and

actuation means, responsive to at least a predetermined one of said maxima and minima signals, for generating an actuation signal in response to said predetermined one of said extrema signals, the improvement wherein said respiration monitor further comprises;

time domain discriminator means, responsive to at least said predetermined one of said maxima and minima signals, for inhibiting said actuation means with respect to a particular predetermined one of said maxima and minima if said particular predetermined one of said maxima or minima occurs within a first proscribed time period from a preceding predetermined one of said maxima and minima, and for inhibiting said actuation means with respect to said particular one of said maxima or minima if said particular one occurs within a second proscribed time period of a minima or maxima of the opposite type.

104. The apparatus of claim 103 wherein said first proscribed time period is approximately 333 msec.

105. The apparatus of claims 103 or 104 wherein said predetermined one of maxima and minima is a maxima and said second proscribed time period is approximately 111 msec.

106. The apparatus of claims 103 or 104 wherein said predetermined one of maxima and minima is a minima and said second proscribed time period is approximately 222 msec.

107. The apparatus of claim 103 wherein said first proscribed time period is in accordance with a predetermined physiologically maximum respiration rate for said subject.

108. The apparatus of claims 103 or 107 wherein said second proscribed time period is in accordance with a predetermined minimum time period between physiological occurrences of successive particular one of said maxima or minima and said maxima or minima of the other type.

109. Apparatus for generating an analog signal indicative of the respiration of a subject comprising:

current source means, for generating an on-off modulated constant current signal;

electrodes, electrically coupled to said current source means for passing said on-off modulated constant current signal through said body;

a high input impedance differential amplifier, DC coupled to said electrodes for developing a modulated impedance signal having an AC component indicative of the change in the transthoracic impedance of said subject;

a phase synchronous demodulator, responsive to said modulated impedance signal and a signal indicative of said on-off modulated constant current signal, for generating a demodulated impedance signal indicative of the transthoracic impedance of said subject and including said AC component; and

first low pass filter means, responsive to said demodulated impedance signal, for generating said analog respiration signal;

means, responsive to said modulated impedance signal, for generating a signal representative of common mode signals between said electrodes; and

means for inverting said signal indicative of common mode signals and applying said inverted signal as an input signal to said differential amplifier.

110. The respiration monitor of claim 109 wherein said apparatus is disposed in a conductive shielding structure and said apparatus further includes:

means for applying said inverted signal to said conductive shielding structure to substantially reduce electromagnetic interference to said apparatus.

111. An apparatus comprising:

means for generating an analog signal indicative of a physiological occurrence in a subject, said analog signal including a DC component and an AC component, said AC component representing information in respect of said physiological occurrence and having known maximum amplitudes;

means, responsive to said analog signal, for generating sequential samples indicative of said analog signal;

storage means, responsive to said sequential sample and to a control signal applied thereto, for storing, in response to said control signal, a selected one of said sequential samples as a base level sample;

means for generating a difference signal indicative of the differences between each respective sample, in sequence, and said base level sample;

means for providing a threshold signal indicative of a preset threshold value in accordance with said known maximum amplitude;

means, responsive to said threshold signal and said difference signal for sequentially comparing the differences associated with the respective sequential samples to a preset threshold, and selectively generating, in accordance with the comparision, said control signal to said storage means to effect storage of the respective sequential sample as said base level sample;

means for generating an offset compensated signal indicative of said analog signal minus said base level sample; and

processing means for analyzing said offset compensated signal.

112. The apparatus of claims 81 or 111 wherein said means for generating said analog signal comprises means for generating a signal indicative of the transthoracic impedance of said subject and said predetermined threshold value is in the range of a value equivalent to 10 ohms to a value equivalent to 30 ohms.