Method and apparatus for discriminating between valid and artifactual pulse waveforms in pulse oximetry

• US 5,588,425 A
• Filed: 05/01/1995
• Issued: 12/31/1996
• Est. Priority Date: 05/21/1993
• Status: Expired due to Term

• Current Assignee: Adidas AG
• Original Assignee: NIMS Incorporated
• Inventors: Inman, Dana M., Sackner, Marvin A.
• Primary Examiner(s): Sykes, Angela D.
• Assistant Examiner(s): GILBERT, SAMUEL G
• Application Number:
  US08/431,469
• Time in Patent Office: 610 Days
• Field of Search: 128/632-635, 128/670, 128/671, 128/696, 128/700, 128/703, 128/704, 128/706, 128/708, 128/715, 128/664, 128/665, 356/39, 356/40, 356/41, 607/25, 364/413.03, 364/413.09
• US Class Current: 600/523
• CPC Class Codes: A61B 5/0245 by using sensing means generating electric signals, i.e. ECG signals
• CPC Class Codes: A61B 5/0809 by impedance pneumography
• CPC Class Codes: A61B 5/1135 by monitoring thoracic expansion

Abstract

A method and apparatus for use in pulse oximetry for discriminating between valid pulse waveforms and artifactual pulse waveforms. Systolic upstroke times for valid pulse waveforms are in a consistent, narrow range which varies only slightly from subject to subject. This narrow range, which may be defined empirically for each subject or established by a default setting applicable to all subjects, defines a predetermined range of systolic upstroke times indicative of valid pulse waveforms. The systolic upstroke time of each pulse waveform is compared against the predetermined range, and pulse waveforms are deemed valid only if their systolic upstroke times are within the predetermined range. Only arterial oxygen saturation levels based on validated pulse waveforms are accepted. The present invention may also be used to validate the heart rate and/or R-R, intervals of an ECG, and for discriminating between sleep and wakefulness in a monitored subject.

Claims

1. A method for discriminating between artifactual and non-artifactual pulse waveforms generated by a pulse oximeter for validating indicated arterial oxygen saturation levels of a subject also generated by the pulse oximeter, the pulse waveforms each being defined, at least partially, by a systolic upstroke time and a diastolic time, the method comprising:

selecting a predetermined range of a first parameter indicative of a correct pulse waveform, said first parameter being selected from the group consisting of systolic upstroke times and diastolic times;

receiving from the pulse oximeter, in a first receiving step, pulse waveforms;

receiving from the pulse oximeter, in a second receiving step, signals indicative of the arterial oxygen saturation level of the subject;

measuring said first parameter of the received pulse waveforms, wherein said measuring step comprises measuring the systolic upstroke times corresponding to received pulse waveforms;

comparing the measured systolic upstroke times to a predetermined range of, systolic upstroke times;

rejecting as artifactual any of the pulse waveforms having a systolic upstroke time outside said predetermined range of systolic upstroke times; and

determining the arterial oxygen saturation levels indicated by the received signals corresponding temporally to the non-rejected pulse waveforms.

2. The method of claim 1, wherein said predetermined range is determined to be from about 0.09 seconds to about 0.21 seconds.

3. The method of claim 1, wherein said received pulse waveforms and signals correspond to output by a pulse oximeter, said method further comprising rejecting arterial oxygen saturation levels of the subject determined from said signals received during time periods respectively corresponding to rejected pulse waveforms.

4. The method of claim 3, wherein said step of rejecting said arterial oxygen saturation levels comprises rejecting said arterial oxygen saturation levels on a real time basis.

5. The method of claim 4, further comprising the step of storing arterial saturation levels derived from signals generated by the pulse oximeter during times other than those respectively corresponding to rejected pulse waveforms.

6. The method of claim 1, further comprising a step of generating pulse waveforms, the pulse waveforms each being defined, at least partially, by a systolic upstroke time and a diastolic time, with a pulse oximeter prior to said first receiving step.

7. The method of claim 1, further comprising the steps of monitoring said subject for generating a signal indicative of a heart rate of the subject;

determining a pulse rate from the received pulse waveforms; and

validating the heart rate of the subject only when the pulse rate of the non-rejected pulse waveforms is approximately equal to the heart rate indicated by said signal.

8. A method for discriminating between artifactual and non-artifactual pulse waveforms for validating indicated arterial oxygen saturation levels of a subject, the pulse waveforms each being defined, at least partially, by a systolic upstroke time and a diastolic time, the method comprising:

receiving pulse waveforms;

measuring, in a first measuring step, a first parameter of the received pulse waveforms selected from the group consisting of the systolic upstroke times and diastolic times;

comparing the measured first parameter to a predetermined range of the first parameter indicative of a correct pulse waveform;

rejecting as artifactual any of the received pulse waveforms having a said measured first parameter outside said predetermined range of the first parameter;

measuring, in a second measuring step, the first parameter for as plurality of pulse waveforms generated prior to said first measuring step; and

determining said predetermined range from selected first parameter values measured during said second measuring step, wherein said step of determining said predetermined range comprises;

determining a second parameter selected from a mean and median of the selected first parameter for said plurality of pulse waveforms of said second measuring step, and

establishing said predetermined range as within a predetermined time interval having a minimum less than said second parameter and a maximum greater than said second parameter.

9. The method of claim 8, further comprising the step of verifying that said plurality of pulse waveforms have normal waveforms.

10. A method for discriminating between artifactual and non-artifactual pulse waveforms for validating indicated arterial oxygen saturation levels of a subject, the pulse waveforms each being defined, at least partially, by a systolic upstroke time and a diastolic time, the method comprising:

receiving pulse waveforms;

measuring a first parameter of the received pulse waveforms selected from the group consisting of the systolic upstroke times and diastolic times;

comparing the measured first parameter to a predetermined range of the first parameter indicative of a correct pulse waveform;

rejecting as artifactual any of the pulse waveforms having a said measured first parameter outside said predetermined range of the first parameter; and

determining whether said subject is asleep or awake by classifying said subject as awake during time intervals corresponding to rejected pulse waveforms and as asleep during time intervals corresponding to non-rejected pulse waveforms.

11. The method of claim 10, further comprising the step of monitoring said subject'"'"'s breathing and wherein said classifying step comprises classifying said subject as awake only when said rejected pulse waveforms persist for at least one breath.

12. A method for discriminating between artifactual and non-artifactual pulse waveforms for validating a heart rate of a subject, the pulse waveforms each being defined, at least partially, by a systolic upstroke time and a diastolic time, the method comprising:

receiving pulse waveforms;

measuring a first parameter of the received pulse waveforms selected from the group consisting of the systolic upstroke times and diastolic times;

comparing the measured first parameter to a predetermined range of the first parameter indicative of a correct pulse waveform;

rejecting as artifactual any of the pulse waveforms having a said measured first parameter outside said predetermined range of the first parameter;

monitoring said subject with an ECG for generating a signal indicative of the heart rate of the subject;

determining a pulse rate from pulse waveforms not rejected at said rejecting step; and

validating the heart rate of the subject only when the pulse rate of the non-rejected pulse waveforms is approximately equal to the heart rate.

13. The method of claim 12, wherein said step of validating said heart rate further comprises validating said heart rate on a real time basis.

14. The method of claim 13, further comprising the step of storing data corresponding to the heart rate when the heart rate is validated.

15. The method of claim 12, wherein said step of validating the heart rate of the subject further comprises validating R-R intervals of the subject.

16. An apparatus for discriminating between artifactual and non-artifactual pulse waveforms for validating indicated arterial oxygen saturation levels of a subject, the pulse waveforms each being defined, at least partially, by a systolic upstroke time and a diastolic time, the apparatus comprising:

means for selecting a predetermined range of a first parameter indicative of a correct pulse waveform, said selecting means selecting said first parameter from the group consisting of systolic upstroke times and diastolic times;

first means for receiving pulse waveforms;

second means for receiving signals indicative of the arterial oxygen saturation level of the subject;

means for measuring said first parameter of the pulse waveforms received by said first receiving means, wherein said means for measuring is operative to measure systolic upstroke times of the received pulse waveforms;

means for comparing the measured systolic upstroke times to the predetermined range of systolic upstroke times selected by said selecting means;

means for rejecting as artifactual any of the received pulse waveforms corresponding to measured systolic upstroke times outside said predetermined range of systolic upstroke times; and

means for determining the arterial oxygen saturation levels indicated by the received signals corresponding temporarily to the non-rejected pulse waveforms.

17. The apparatus of claim 16, wherein said predetermined range is from about 0.009 seconds to about 0.21 seconds.

18. The apparatus of claim 16, wherein said received pulse waveforms and signals correspond to output by a pulse oximeter, said apparatus further comprising means for rejecting arterial oxygen saturation levels of the subject determined from said signals received during time periods corresponding to respective rejected pulse waveforms.

19. The apparatus of claim 18, wherein said means for rejecting said arterial oxygen saturation levels is operative to reject said arterial oxygen levels on a real time basis.

20. The apparatus of claim 19, further comprising means for storing arterial oxygen saturation levels derived from said signals generated by the pulse oximeter during times other than those corresponding to rejected pulse waveforms.

21. The apparatus of claim 16, further comprising a pulse oximeter for generating at least some of the pulse waveforms received by said first receiving means.

22. The apparatus of claim 16, wherein the received pulse waveforms correspond to output by a pulse oximeter, said apparatus further comprising means for generating a signal indicative of a heart rate of the subject;

means for determining a pulse rate from the received pulse waveforms; and

means for indicating that the pulse rate of the non-rejected pulse waveforms is approximately equal to the heart rate indicated by said signal.

23. An apparatus for discriminating between artifactual and non-artifactual pulse waveforms for validating indicated arterial oxygen saturation levels of a subject the pulse waveforms each being defined, at least partially, by a systolic upstroke time and a diastolic time, the apparatus comprising:

means for receiving pulse waveforms;

first means for measuring a first parameter of said received pulse waveforms, said measured first parameter being selected from the group consisting of the systolic upstroke times and diastolic times;

second means for measuring the first parameter for a plurality of waveforms generated prior to the pulse waveforms received by said first means for receiving;

means for determining a predetermined range of the first parameter indicative of a correct pulse waveform from said measured first parameter of said pulse waveforms, wherein said means for determining said predetermined range is operative to determine one of a mean and median of said selected one of said systolic upstroke times and diastolic times for said prior generated plurality of pulse waveforms and to establish as said predetermined range a predetermined time interval having a minimum less than one of said mean and median and a maximum greater than one of said mean and median;

means for comparing the measured first parameter of said pulse waveforms to said predetermined range of the first parameter; and

means for rejecting as artifactual any of the received pulse waveforms having a said measured first parameter outside said predetermined range of the first parameter.

24. The apparatus of claim 23, further comprising means for verifying that said prior generated plurality of pulse waveforms have normal waveforms.

25. An apparatus for discriminating between artifactual and nonartifactual pulse waveforms for validating indicated arterial oxygen saturation levels of a subject, the pulse waveforms each being defined, at least partially, by a systolic upstroke time and a diastolic time, the apparatus comprising:

means for receiving pulse waveforms;

means for measuring a first parameter of said received pulse waveforms, said measured first parameter being selected from the group consisting of the systolic upstroke times and diastolic times;

means for comparing the measured first parameters to a predetermined range of the first parameter indicative of a correct pulse waveform;

means for rejecting as artifactual any of the received pulse waveforms having a said measured first parameter outside the predetermined range of the first parameter; and

means for classifying said subject as awake during first time intervals corresponding to rejected pulse waveforms and as asleep during second time intervals corresponding to non-rejected pulse waveforms.

26. The apparatus of claim 25, further comprising means for monitoring said subject'"'"'s breathing and wherein said means for classifying comprises means for classifying said subject as awake only when said rejected pulse waveforms persist for at least one breath.

27. The apparatus of claim 26, wherein said indicating means is operative to indicate, on a real-time basis, that the pulse rate of non-rejected pulse waveforms is approximately equal to the heart rate.

28. The apparatus of claim 27, furthe comprising means for storing data corresponding to the heart rate when the heart rate is approximately equal to the pulse rate.

29. An apparatus for discriminating between artifactual and non-artifactual pulse waveforms for validating a heart rate of a subject, the pulse waveforms each being defined, at least partially, by a systolic upstroke time and a diastolic time, the apparatus comprising:

means for receiving the pulse waveforms corresponding to pulse signals output by a pulse oximeter;

means for measuring a first parameter of said received pulse waveforms selected from the group consisting of the systolic upstroke times and diastolic times;

means for comparing the measured first parameter to a redetermined range of the first parameter indicative of a correct pulse waveform;

means for rejecting as artifactual any of the received pulse waveforms having a said measured first parameter outside said predetermined range of the first parameter;

an ECG for generating a signal indicative of a heart rate of the subject;

means for determining a pulse rate from the pulse waveforms generated by the pulse oximeter; and

means for indicating that the pulse rate of non-rejected pulse waveforms is approximately equal to the heart rate.