Method for detecting an irregular state in a non-invasive pulse oximeter system

• US 5,517,988 A
• Filed: 09/19/1994
• Issued: 05/21/1996
• Est. Priority Date: 12/11/1993
• Status: Expired due to Term

• Current Assignee: Philips Electronics North America Corporation (Koninklijke Philips N.V.)
• Original Assignee: Hewlett-Packard Company (HP Inc.)
• Inventors: Gerhard, Klamser
• Primary Examiner(s): Sykes, Angela D.
• Assistant Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US08/308,381
• Time in Patent Office: 610 Days
• Field of Search: 128/633, 356/41
• US Class Current: 600/323
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/6824 Arm or wrist
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/6838 Clamps or clips

Abstract

A method and an apparatus enable detection of an irregular state in a non-invasive pulse oximeter system. The system comprises an oxygen saturation sensing probe for generating spectrophotometric signals and an oxygen saturation computing section for deriving arterial hemoglobin oxygen saturation from the spectrophotometric signals. Irregular states of the system are detected by pre-defining at least one criterion for distinguishing between spectrophotometric signals indicative of the normal state of the system and spectrophotometric signals generated by the pulse oximeter system when a predetermined non-physiological event occurs. Then it is judged whether the actual spectrophotometric signals fulfill this criterion. The presence of the irregular state is detected if the actual criterion fulfill the criterion.

Claims

1. A method of detecting an irregular state in a non-invasive pulse oximeter system, said system comprising means for generating a spectrophotometric signal, and oxygen saturation computing means for deriving arterial hemoglobin oxygen saturation from the spectrophotometric signal, said method comprising the steps of:

low pass filtering said spectrophotometric signal to establish a low pass filtered spectrophotometric signal;

high pass filtering the spectrophotometric signal to establish a high pass filtered spectrophotometric signal;

determining if conditions a-d, as recited hereafter, are simultaneously fulfilled;

(a) an amplitude of the low pass filtered spectrophotometric signal falls in a tolerance interval;

(b) an amplitude of the high pass filtered spectrophotometric signal does not exceed a threshold;

(c) said amplitude of the high pass filtered spectrophotometric signal falls within a predetermined transition characteristic; and

(d) a non-pulsatile alarm is generated by said non-invasive pulse oximeter system;

signalling a presence of an irregular state indicative of a predetermined non-physiological event if the spectrophotometric signal fulfills all said conditions.

2. The method as set forth in claim 1, further comprising:

disposing an oxygen saturation probe of said non-invasive pulse oximeter system on a finger of a patient'"'"'s arm, and wherein an inflation of a blood pressure cuff wrapped about said patient'"'"'s arm causes said irregular state.

3. The method as set forth in claim 1, wherein the non-physiological event results from an inflation of a cuff wrapped about a patient'"'"'s arm and wherein the method further comprises the steps of:

setting a state machine in a first state if conditions hereafter recited are simultaneously fulfilled;

said amplitude of the low pass filtered spectrophotometric signal falls in the tolerance interval;

said amplitude of the high pass filtered spectrophotometric signal does not exceed the threshold;

said amplitude of the high pass filtered spectrophotometric signal falls within the predetermined transition characteristic; and

the non-invasive pulse oximeter system generates the non-pulsatile alarm; and

setting said state machine in a second state when detecting a new pulsation or when a predetermined time has expired after being set in the first state.

4. An apparatus for detecting an irregular state in a non-invasive oximeter system, said system comprising means for generating a spectrophotometric signal, and oxygen saturation computing means for deriving arterial hemoglobin oxygen saturation from the spectrophotometric signal, said irregular state detecting apparatus comprising:

low pass filter means for establishing a low pass filtered spectrophotometric signal from said spectrophotometric signal;

a high pass filter means for establishing a high pass filtered spectrophotometric signal from said spectrophotometric signal;

storing means for storing conditions for distinguishing between a spectrophotometric signal indicative of a normal state and a spectrophotometric signal generated by said non-invasive pulse oximeter system when a predetermined non-physiological event occurs, the conditions being as follows;

an amplitude of the low pass filtered spectrophotometric signal falls in a tolerance interval;

an amplitude of the high pass filtered spectrophotometric signal does not exceed a threshold; and

said amplitude of the high pass filtered spectrophotometric signal falls within a predetermined transition characteristic;

judging means responsive to at least said low pass filtered spectrophotometric signal, said high pass filtered spectrophotometric signal and said conditions, for judging whether said spectrophotometric signal fulfills said conditions; and

means for signalling a presence of an irregular state indicative of a predetermined non-physiological event if said spectrophotometric signal fulfills said conditions.

5. In a non-invasive pulse oximeter system for measuring the arterial hemoglobin oxygen saturation and for performing a method of suppressing a false alarm caused by a non-physiological event, said non-invasive pulse oximeter system comprising:

an oxygen saturation sensing probe with light source means for generating light of different wavelengths transmitted through an area of a patient'"'"'s body and with light detector means for receiving light of the different wavelengths and for generating a spectrophotometric signal;

a pulse finding means responsive to said spectrophotometric signal for generating a pulse detection signal;

oxygen saturation computing means responsive to said spectrophotometric signal and responsive to said pulse detection signal, for deriving a diastolic spectrophotometric signal and a systolic spectrophotometric signal, for computing relative absorption ratios based on said diastolic spectrophotometric signal and said systolic spectrophotometric signal and for computing arterial oxygen saturation from said relative absorption ratios; and

alarm means for generating an alarm if said pulse finding means fails to detect a pulse or if a measured arterial oxygen saturation and/or a measured patient pulse rate fall outside of a predetermined tolerance band width;

means for low pass filtering of the spectrophotometric signal for establishing a low pass filtered spectrophotometric signal;

means for high pass filtering of the spectrophotometric signal for establishing a high pass filtered spectrophotometric signal;

means for judging whether the spectrophotometric signal simultaneously fulfills the following conditions;

an amplitude of the low pass filtered spectrophotometric signal falls in a tolerance interval;

an amplitude of the high pass filtered spectrophotometric signal does not exceed a threshold;

said amplitude of the high pass filtered spectrophotometric signal falls within a predetermined transition characteristic; and

a non-pulsatile alarm is generated by said alarm means;

means for signalling a presence of an irregular state indicative of a predetermined non-physiological event if the spectrophotometric signal fulfills said conditions and suppressing the alarm generated by said alarm means upon the presence of said irregular state.

6. An alarm system for suppressing a false alarm caused by a non-physiological event in a non-invasive pulse oximeter system for measuring arterial hemoglobin oxygen saturation, said pulse oximeter system comprising:

oxygen saturation sensing probe means with light source means for generating light of different wavelengths transmitted through an area of the patient'"'"'s body and with light detector means for receiving light of the different wavelengths and for generating a spectrophotometric signal;

a pulse finding means responsive to said spectrophotometric signal for generating a pulse detection signal;

oxygen saturation computing means responsive to said spectrophotometric signal and responsive to said pulse detection signal, for deriving a diastolic spectrophotometric signal and a systolic spectrophotometric signal, for computing relative absorption ratios based on said spectrophotometric diastolic signal and said systolic spectrophotometric signal and for computing arterial oxygen saturation from said relative absorption ratios; and

alarm means for generating an alarm if said pulse finding means fails to detect a pulse or if a measured arterial oxygen saturation and/or a measured pulse rate fall out of predetermined tolerance band widths;

said alarm means including means for suppressing the false alarm comprising;

a low pass filter for establishing a low pass filtered spectrophotometric signal from a spectrophotometric signal;

a high pass filter for establishing a high pass filtered spectrophotometric signal from a spectrophotometric signal;

storing means for storing conditions for distinguishing between a spectrophotometric signal indicative of a normal state of said non-invasive pulse oximeter system and a spectrophotometric signal generated by said non-invasive pulse oximeter system when a predetermined non-physiological event occurs, the conditions being as follows;

an amplitude of the low pass filtered spectrophotometric signal falls in a tolerance interval;

an amplitude of the high pass filtered spectrophotometric signal does not exceed a threshold;

said amplitude of the high pass filtered spectrophotographic signal falls within a predetermined transition characteristic;

said non-invasive pulse oximeter system generates a non-pulsatile alarm;

judging means for judging whether said spectrophotometric signal fulfills all said conditions;

means for signalling a presence of an irregular state indicative of a predetermined non-physiological event if said spectrophotometric signal fulfills all said conditions; and

alarm suppressing means for suppressing an alarm generated by said alarm means.