Oximeter with motion detection for alarm modification

• US 5,662,106 A
• Filed: 01/29/1996
• Issued: 09/02/1997
• Est. Priority Date: 03/26/1993
• Status: Expired due to Fees

• Current Assignee: Nellcor Incorporated (Medtronic Plc)
• Original Assignee: Nellcor Incorporated (Medtronic Plc)
• Inventors: Swedlow, David B., Potratz, Robert S.
• Primary Examiner(s): Sykes, Angela D.
• Assistant Examiner(s): WINAKUR, ERIC FRANK
• Application Number:
  US08/593,188
• Time in Patent Office: 582 Days
• Field of Search: 128/633, 128/664-667, 364/413.03, 356/41
• US Class Current: 600/331
• CPC Class Codes: A61B 5/1104 induced by stimuli or drugs; A61B5/1102 takes precedence; investigating medicinal preparations G01N33/15
• CPC Class Codes: A61B 5/14551 for measuring blood gases
• CPC Class Codes: A61B 5/6826 Finger
• CPC Class Codes: A61B 5/7207 of noise induced by motion artifacts
• CPC Class Codes: A61B 5/721 using a separate sensor to detect motion or using motion information derived from signals other than the physiological signal to be measured
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 5/746 Alarms related to a physiological condition, e.g. details of setting alarm thresholds or avoiding false alarms alarms per se G08B

Abstract

A pulse oximeter which modifies the alarm condition when motion is detected. Basically, if the lack of a pulse is determined to be as a result of motion artifact, the generation of an alarm is postponed. In addition, the display indicates that motion is present and that the last reading is questionable due to the presence of motion. The invention also determines if motion artifact is present from the pulse oximeter detector signal itself. The ratio of the positive and negative peaks of the derivative of the pulse signal are compared to a motion/blood pulse threshold.

Claims

1. A method of operating a pulse oximeter which emits light, the method comprising the steps of:

(a) qualifying pulses in a detector signal, the detector signal corresponding to absorption by blood constituents of the light emitted by the oximeter;

(b) upon a condition suggesting a possible alarm situation, setting a first timer, the first timer expiring upon elapse of a time interval of a first predetermined duration;

(c) if a pulse is detected in the detector signal after the first timer has been set and before the first timer expires, performing the steps of;

(c1) determining if the pulse has resulted from motion artifact; and

(c2) if the pulse is determined to have resulted from motion artifact, resetting the first timer; and

(d) if and when the first timer expires, generating an alarm.

2. The method of claim 1, wherein step (c2) resets the first timer to expire upon elapse, from when step (c2) is performed, of a time interval of the first predetermined duration.

3. The method of claim 1, wherein the condition suggesting a possible alarm situation arises upon elapse of a time interval of a predetermined length during which a qualified pulse is not detected.

4. The method of claim 3, wherein the predetermined length is approximately 10 seconds.

5. The method of claim 1, wherein the first predetermined duration is approximately 6.3 seconds.

6. The method of claim 1, further comprising the step of:

(e) upon the condition suggesting a possible alarm situation, setting a second timer, the second timer expiring upon elapse of a time interval of a second predetermined duration, the second predetermined duration being larger than the first predetermined duration; and

(f) if and when the second timer expires, generating the alarm.

7. The method of claim 6, wherein the second predetermined duration is approximately 50 seconds.

8. The method of claim 6, further comprising the step of:

(g) if a predetermined number of qualified pulses are detected before either the first timer or the second timer expires, stopping the first and second timers.

9. The method of claim 8, wherein the predetermined number is approximately 4.

10. The method of claim 1, wherein step (c) further comprises the steps of:

(c3) determining if the pulse has resulted from noise; and

(c4) if the pulse is determined not to have resulted from noise, resetting the first timer.

11. The method of claim 10, wherein step (c4) resets the first timer to expire upon elapse, from when step (c4) is performed, of a time interval of the first predetermined duration.

12. A method of operating a pulse oximeter which emits light, the method comprising the steps of:

(a) qualifying pulses in a detector signal until a time interval of a predetermined length elapses during which a qualified pulse is not detected, the detector signal corresponding to absorption by blood constituents of the light emitted by the oximeter;

(b) if and when step (a) terminates, setting a count to zero and setting a first timer, the first timer expiring upon elapse of a time interval of a first predetermined duration;

(c) after each of steps (b), (e) and (h), setting a second timer, the second timer expiring upon elapse of a time interval of a second predetermined duration, the second predetermined duration being smaller than the first predetermined duration;

(d) after step (c), if a pulse is detected in the detector signal after the second timer has been set in step (c) and before the second timer expires, determining if the pulse has resulted from motion artifact and determining if the pulse has resulted from noise;

(e) after step (d), if the pulse is determined to have resulted from motion artifact, stopping the second timer and repeating steps (c) through (h);

(f) after step (d), if the pulse is determined to have resulted neither from motion artifact nor from noise, incrementing the count by one, the count indicating a number of qualified pulses detected since step (b) was last performed;

(g) after step (f), if the count is equal to a predetermined number, stopping the first and second timers, and repeating steps (a) through (h);

(h) after step (f), if the count is not equal to the predetermined number, stopping the second timer and repeating steps (c) through (h); and

(i) if and when either the first or the second timer expires, generating an alarm.

13. The method of claim 12, wherein the predetermined length is approximately 10 seconds.

14. The method of claim 12, wherein the first predetermined duration is approximately 50 seconds.

15. The method of claim 12, wherein the second predetermined duration is approximately 6.3 seconds.

16. The method of claim 12, wherein the predetermined number is approximately 4.

17. A pulse oximeter comprising:

an emitter for emitting light;

a photodetector for producing an analog detector signal corresponding to absorption of said light by blood constituents;

a circuit, coupled to the photodetector, for producing a digital detector signal corresponding to the analog detector signal; and

a processor, coupled to said circuit and programmed to;

(a) qualify pulses in the digital detector signal corresponding to arterial pulses;

(b) generate an alarm when no qualified pulses are detected in a time-out period; and

(c) modify the timing of the generation of said alarm if the processor determines that motion artifact is present during said time-out period.

18. The apparatus of claim 17, wherein the processor determines whether motion artifact is present during said time-out period by analyzing the digital detector signal.

19. The apparatus of claim 17, wherein the processor determines whether motion artifact is present during said time-out period by analyzing a signal generated by a motion detector attached to the pulse oximeter.

20. An apparatus for detecting motion artifact in a digital pulse oximeter signal comprising:

an emitter for emitting light at a body;

a photodetector for producing an analog detector signal corresponding to absorption of said light by the body;

a circuit, coupled to the photodetector, for producing the digital pulse oximeter signal from the analog detector signal; and

a processor, coupled to said circuit and programmed to;

(a) detect a pulse waveform in said digital pulse oximeter signal;

(b) determine the derivative of said pulse waveform;

(c) determine the ratio of a positive peak of said derivative to a negative peak of said derivative;

(d) compare said ratio to a threshold value; and

(e) indicate motion artifact when said ratio is less than said threshold.