Respiration monitoring method and apparatus

• US 3,911,899 A
• Filed: 11/08/1973
• Issued: 10/14/1975
• Est. Priority Date: 11/08/1973
• Status: Expired due to Term

• Current Assignee: Allied Healthcare Products Incorporated
• Original Assignee: Neil R. Hattes
• Inventors: Hattes, Neil R.
• Primary Examiner(s): Kamm, Willam E.
• Application Number:
  US05/414,041
• Time in Patent Office: 705 Days
• Field of Search: 128/2R,2S,2.5P,2.5R,2.5T,2.6A,2.6F,2.6R,2.08,2.1R,2.1Z,145.5
• US Class Current: 600/407
• CPC Class Codes: A61B 5/113 occurring during breathing

Abstract

Circuitry for measuring and displaying periodically occurring physiological parameters such as the breathing rate of a patient and for providing an alarm upon the occurrence of abnormal rates is disclosed. Patient breathing is detected by variations in the distance between transmsitter and receiver coils, with respiratory movement producing a change in the magnetic field detected by the receiver coil. The resulting current is amplified and shaped to produce a breathing waveform. This signal is fed to an inspiration detector which is reflexive so that a second breath cannot be detected until there has been a definite expiration of the first breath. The output from the inspiration detector is a series of pulses representative of the breathing rate; these pulses are fed to an alarm circuit which compares the detected rates with values preset by an operator. The rate pulses are also fed to a lamp to provide a visual output indicative of the occurrence of a breath and are fed to a rate-meter for displaying the number of breaths per minute averaged over a 30 second time interval.

Claims

1. In a monitor, circuitry for measuring the rate of recurrence of a physiological parameter of a patient and for providing an alarm upon variation of the parameter from preselected values;

sensing means responsive to said parameter for producing a sensing signal;

first integrator means responsive to said sensing signal to produce a variable parameter signal;

second integrator means responsive to said variable parameter signal to produce a relatively stable base signal;

differential amplifier means responsive to the difference between said base and variable parameter signals to produce an electrical signal having a waveform the slope and amplitude of which varies in accordance with the parameter being monitored;

reflexive means responsive to said electrical signal for detecting said rate of recurrence, said reflexive means being responsive to a recurring slope of said waveform, whereby a waveform having a slope of a first direction initiates a pulse, said reflexive means preventing the production of a second pulse until said waveform reverses to a second direction and returns to said first direction to thereby define a complete cycle of said parameter and a recurrence of the parameter being measured;

first adjustable alarm means responsive to the rate of recurrence of said pulses to produce a first alarm signal when said rate exceeds a first preset value;

second adjustable alarm means responsive to the rate of recurrence of said pulses to produce a second alarm signal when said rate falls below a second preset value; and

indicator means responsive to said alarm signals.

2. The monitor of claim 1, wherein:

said first integrator means has a relatively short time constant; and

said second integraTor means has a relatively long time constant.

3. The monitor of claim 2, wherein said sensing means further includes a sensor responsive to magnetic fields modulated in accordance with variations in said parameter to produce said electrical signal, said parameter being the inspiration and expiration motions of the patient, whereby said waveform of said electrical signal corresponds to the breathing profile of the patient.

4. The monitor of claim 1 wherein said first alarm means incorporates a first alarm timer for measuring intervals between successive pulses and producing an excessive pulse rate output signal whenever the interval between two successive pulses is less than a predetermined period, and first register means responsive only to the occurrence of three successive excess pulse rate output signals from said first timer to produce said first alarm signal.

5. The monitor of claim 4, wherein said second alarm means incorporates a second alarm timer for measuring intervals between successive pulses and producing a low pulse rate signal whenever the interval between two successive pulses is greater than a predetermined period, and second register means responsive to a low pulse rate signal from said second timer to produce said second alarm signal.

6. The monitor of claim 5, further including third adjustable alarm means responsive to the rate of recurrence of said pulses to produce a third alarm signal if a following pulse is not received within a preset period of time after the end of a prior pulse.

7. The monitor of claim 6, wherein said third alarm means incorporates a third alarm timer, and third register means responsive to an output signal from said third timer to provide said third alarm signal.

8. The monitor of claim 7, further including reset means for resetting said third alarm timer upon the occurrence of a pulse prior to the completion of the preset period of time for said third timer.

9. The monitor of claim 1, wherein said reflexive means comprises amplifier means having an input and an output;

positive feedback means connected between the output and the input of said amplifier; and

AC coupling means coupling said electrical signal to the input of said amplifier means whereby said amplifier is responsive to changes in the slope of the waveform of said electrical signal to produce at its output pulses having a repetition rate corresponding to the rate of recurrence of said parameter.

10. In a monitor, circuitry for measuring the rate of recurrence of a physiological parameter of a patient and for providing an alarm upon variation of the parameter from preselected values, comprising:

sensing means for producing an electrical signal having a waveform which varies in accordance with said parameter;

detecting means responsive to the waveform of said electrical signal to produce rate pulses corresponding to the occurrence of said parameter;

first adjustable alarm means responsive to the rate of recurrence of said rate pulses to produce a first alarm signal when the rate of recurrence exceeds a first preset alarm condition value;

second adjustable alarm means responsive to the rate of recurrence of said rate pulses to produce a second alarm signal when the rate of recurrence falls below a second preset alarm condition value;

third adjustable alarm means responsive to the rate of recurrence of said pulses to produce a third alarm signal if a following pulse is not received within a preset period of time after the end of a prior pulse;

a clock pulse generator responsive to each said rate pulse to produce first and second phase pulses;

means to apply each of said first phase pulses to said first and second alarm means to produce alarm signals when an alarm condition exists; and

means to apply each of said second phase pulses to said first, second and third alarm means to prevent the production of alarm signals when no alarm condition exists.

11. The monitor of claim 10, wHerein said means to apply said second phase pulses to said alarm means includes a reset network, said reset network further including manual reset means and first breath lockout means.

12. The monitor of claim 10, wherein said first alarm means incorporates a first alarm timer for measuring intervals between successive rate pulses and producing an alarm condition output signal whenever the interval between two successive pulses is less than a predetermined period, and first register means responsive to a plurality of successive alarm condition output signals to produce said first alarm signal.

13. The monitor of claim 12, wherein said second alarm means incorporates a second alarm timer for measuring intervals between successive rate pulses and producing a low pulse rate signal whenever the interval between two successive rate pulses is greater than a predetermined period, and second register means responsive to a low pulse rate signal to produce said second alarm signal.

14. The monitor of claim 10, wherein said first alarm means incorporates a first alarm timer for measuring the intervals between successive rate pulses and first register means responsive to said first timer to produce said first alarm signal upon the occurrence of an excessive pulse rate;

said second alarm means incorporates a second alarm timer for measuring the intervals between successive rate pulses and second register means responsive to said second timer to produce said second alarm signal upon the occurrence of an excessive interval between two successive rate pulses to produce said second alarm signal; and

said third alarm means incorporates a third alarm timer and third register means responsive to an output signal from said third timer to provide said third alarm signal.

15. The monitor of claim 14, further including means for applying said first phase pulses to said first and second registers to enable said registers to produce an alarm signal;

and a reset network responsive to said second phase pulses to reset said first, second, and third alarm timers, whereby if an alarm condition exists in said first or second registers, said first phase pulse will cause an alarm signal, and if no alarm condition exists said timers will be reset to monitor the next pulse rate interval.

16. The monitor of claim 15, further including indicator means responsive to said alarm signals and power on clearing means for blanking said indicator means to prevent an indication of an alarm condition for a predetermined time after said monitor is initially turned on.

17. The monitor of claim 16, further including test means for generating pulses at a preselected rate for application to said reset means and for inhibiting the output of said detecting means.

18. The monitor of claim 10, wherein said parameter is the respiration rate of a patient, said sensing means comprising means for measuring the inspiration and expiration motions of the patient to produce a breathing waveform, and wherein said first and second alarm means produce alarm signals in response to rates of inspiration corresponding to said preset alarm condition values, and said third alarm means produces an alarm signal upon the occurrence of apnea.

19. The monitor of claim 18, wherein said sensing means comprises first and second sensor coils and oscillator means connected to said first sensor coil to produce an alternating magnetic field, said second sensor coil being responsive to said magnetic field to produce an output having an amplitude proportional to the spacing between said sensor coils whereby relative motion of said sensor coils amplitude modulates the output of said second sensor coil, and receiver means responsive to said amplitude modulated output to produce said electrical signal having a waveform which varies in accordance with the breathing pattern of said patient.

20. The monitor of claim 10, wherein said sensing means includes:

means responsive to said parameter for producing a seNsing signal;

first integrator means having a relatively short time constant responsive to said sensing signal to produce a variable parameter signal;

second integrator means having a relatively long time constant responsive to said variable parameter signal to produce a relatively stable base signal; and

differential amplifier means responsive to the difference between said base and variable parameter signals to produce said electrical signal having a waveform which varies in accordance with the parameter being monitored.

21. The monitor of claim 20, wherein said detecting means comprises a positive feedback amplifier AC coupled to said differential amplifier means, said detecting means being responsive to the slope of the waveform of said electrical signal to produce said rate pulses.

22. A method of monitoring the respiration rate of a patient comprising:

generating a magnetic field;

modulating said field in accordance with the breathing pattern of the patient;

sensing said field and producing an alternating current signal having an amplitude modulation proportional to said breathing pattern;

converting said alternating current signal to a pulsating direct current signal proportional to said breathing pattern;

integrating said direct current signal over a relatively short time period to produce a first integrated signal;

integrating said first integrated signal over a relatively long time period to produce a second integrated signal;

differentially amplifying said first and second integrated signal to produce a breathing waveform having a base dependent upon the value of said second integrated signal;

producing breathing pulses in response to changes in the direction of slope of said breathing waveform;

sensing the intervals between successive breathing pulses;

comparing the sensed intervals to preselected high rate low rate and apnea values; and

producing alarm signals when said breathing pulses occur at intervals outside said preselected values.

23. The method of claim 22, wherein the steps of sensing and comparing intervals and producing alarm signals comprises:

activating an adjustable high rate timer, an adjustable low rate timer and an adjustable apnea timer upon the occurence of a first breathing pulse;

determining whether either said high rate timer or said low rate timer has timed out upon the occurrence of a second breathing pulse;

producing a first alarm signal if said high rate timer has not timed out, thereby indicating a high breathing rate;

producing a second alarm signal if said low rate timer has timed out, thereby indicating a low breathing rate;

producing a third alarm signal if said apnea timer times out before a second breathing pulse occurs, thereby indicating an apnea condition; and

resetting all of said timers upon receipt of said second pulse.

24. A monitor for providing an alarm upon variation of a measured physiological parameter from preselected values, comprising:

means producing rate pulses corresponding to the rate of recurrence of a measured physiological parameter;

first alarm means including a first alarm timer for measuring the intervals between successive rate pulses and producing an excess pulse rate output signal when any interval is less than a first predetermined period;

first register means responsive to said first timer to produce a first alarm signal upon the occurrence of excess pulse rate output signals corresponding to a plurality of consecutive rate pulses each occurring at intervals less than said first predetermined period;

second alarm means including a second alarm timer for measuring the intervals between successive rate pulses and producing a low rate output signal when any interval is greater than a second predetermined period;

second register means responsive to said second timer to produce a second alarm signal upon the occurrence of a low rate output signal;

reset means respOnsive to each said rate pulse to produce a plurality of sequential phase pulses;

means applying the first-occurring one of said phase pulses to said first and second register means to enable said registers to produce an alarm signal; and

means responsive to the second-occurring one of said phase pulses for resetting said first and second alarm timers, whereby if an alarm condition exists in said first or second registers said first phase pulse will cause an alarm signal, and if no alarm condition exists said timers will be reset to monitor the time period of the next succeeding rate pulse.

25. The monitor of claim 24, further including third alarm means including a third alarm timer for measuring elapsed time between successive rate pulses and producing a third alarm signal if the elapsed time between signals is greater than a third predetermined period, said means responsive to the second-occurring one of said phase pulses further resetting said third alarm timer to prevent production of said third alarm signal and to initiate measurement of the elapsed time to the next succeeding rate pulse.

26. The monitor of claim 25, further including means responsive to a third-occurring one of said phase pulses for restarting said first and second alarm timers.

27. The monitor of claim 24, wherein said first register is responsive only to three consecutive excess rate pulses to produce said first alarm signal.

28. The monitor of claim 24, wherein said parameter is the respiration rate of a patient, and wherein said means for producing rate pulses includes means generating breathing pulses corresponding to the rate of recurrence of successive breath inhalations separated by breath exhalations.

29. IN a monitor, circuitry for measuring the rate of recurrence of a physiological parameter of a patient and for providing an alarm upon variation of the parameter from preselected values;

sensing means for producing an electrical signal having a waveform the slope and amplitude of which varies in accordance with said parameter;

reflexive means for detecting said rate of recurrence, including amplifier means having an input and an output;

positive feedback means connected between the output and the input of said amplifier;

AC coupling means coupling said electrical signal to the input of said amplifier means, said amplifier being responsive to changes in the slope of the waveform of said electrical signal to produce at its output pulses having a repetition rate corresponding to the rate of recurrence of said parameter whereby a waveform having a slope of a first direction initiates a pulse, said reflexive means preventing the production of a second pulse until said waveform reverses to a second direction and returns to said first direction to thereby define a complete cycle of said parameter and a recurrence of the parameter being measured;

first adjustable alarm means responsive to the rate of recurrence of said pulses to produce a first alarm signal when said rate exceeds a first preset value;

second adjustable alarm means responsive to the rate of recurrence of said pulses to produce a second alarm signal when said rate falls below a second preset value; and

indicator means responsive to said alarm signals.