Method and apparatus for monitoring respiration

• US 4,757,824 A
• Filed: 08/15/1986
• Issued: 07/19/1988
• Est. Priority Date: 08/21/1985
• Status: Expired due to Fees

• Current Assignee: Kontron Instruments Holding, N.V.
• Original Assignee: Kontron Holding AG
• Inventors: Chaumet, Serge G. J.
• Primary Examiner(s): Cohen, Lee S.
• Application Number:
  US06/897,476
• Time in Patent Office: 704 Days
• Field of Search: 128/670, 128/671, 128/700, 128/716, 128/721-723, 128/725
• US Class Current: 600/529
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/366 Detecting abnormal QRS complex, e.g. widening
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

A method and an apparatus are provided for monitoring waveforms representing the respiration of a patient and for detecting waveforms having characteristics indicative of apnea. The method comprises processing a first electrical signal having a waveform representing the respiration of the patient and a second electrical signal representing the electrocardiogram of the patient.

In order to increase the reliability of apnea alarms and the accuracy of measuring apnea duration, the method comprises: comparing the amplitude of the first signal, or the amplitude of a signal obtained by transformation of the first signal, at the time of incidence of each QRS complex with a predetermined threshold value, resetting to zero the first signal or said signal obtained by transformation of the first signal in synchronism with the incidence of each QRS complex on the second signal, and triggering an alarm if the amplitudes of the first signal, or of said signal obtained by transformation thereof, at the said times do not exceed the threshold value over a predetermined interval of time, said alarm being indicative of apnea.

Claims

1. A method of monitoring waveforms representing the respiration of a patient and detecting waveforms having characteristics indicative of apnea, comprising processing a first electrical signal having a waveform representing the respiration of the patient and a second electrical signal representing the electrocardiogram of the patient, said method comprising:

(a) forming a third signal which represents the first derivative of the first signal with respect to time,

(b) forming a fourth signal which represents the integral of the third signal over first integration intervals, each of these intervals corresponding to the interval between two successive QRS complexes of the second signal,

(c) comparing the amplitude of the fourth signal at the time of the incidence of each QRS complex which marks the end of one of the said integration intervals with a predetermined threshold value,

(d) resetting to zero the fourth signal in synchronism with the incidence of each QRS complex on the second signal,

(e) forming a fifth signal which represents the integral of the third signal over second integration intervals, each of which is offset by a predetermined interval of time with respect to one of the first integration intervals,

(f) comparing the amplitude of the fifth signal at the time marking the end of each second integration interval with a predetermined threshold value,

(g) resetting to zero the fifth signal at the end of each second integration interval, and

(h) triggering an alarm only if the amplitudes of the fourth signal and the amplitudes of the fifth signal at the end of the respective integration intervals do not exceed the threshold value over a predetermined interval of time, said alarm being indicative of apnea.

2. An apparatus for monitoring the respiration of a patient, comprising means for forming a first electrical signal having a waveform representing the respiration of the patient and a second electrical signal representing the electrocardiogram of the patient, and means for detecting waveforms of the first signal having characteristics indicative of apnea, said means for detecting waveforms comprising:

(a) means for forming a third signal representing the first derivative of the first signal with respect to time,

(b) means for forming a fourth signal representing the integral of the third signal over first integration intervals, each of said intervals corresponding to the interval between two successive QRS complexes of the second signal,

(c) means for comparing the amplitude of the fourth signal at the time of incidence of each QRS complex which marks the end of one of said integration intervals with a predetermined threshold value,

(d) means for resetting the fourth signal to zero in synchronism with the incidence of each QRS complex on the second signal,

(e) means for forming a fifth signal representing the integral of the third signal over second integration intervals, each of which is offset by a predetermined interval of time with respect to one of the first integration intervals,

(f) means for comparing the amplitude of the fifth signal at the time marking the end of each second integration interval with a predetermined threshold value,

(g) means for resetting the fifth signal to zero at the end of each second integration interval, and

(h) means for triggering an alarm if the amplitudes of the fourth signal and the amplitudes of the fifth signal at the end of the respective integration intervals do not exceed the threshold value over a predetermined interval of time, said alarm being indicative of apnea.

3. An apparatus according to claim 2, wherein the means for forming the third signal are filtering means having a frequency attenuation characteristic similar to that of a differentiating circuit.