Detection of electrode/patient motion and fast restore limits

• US 5,247,939 A
• Filed: 01/10/1992
• Issued: 09/28/1993
• Est. Priority Date: 01/10/1992
• Status: Expired due to Term

• Current Assignee: Physio-Control Incorporated (Stryker Corporation)
• Original Assignee: Physio-Control Incorporated (Stryker Corporation)
• Inventors: Taylor, James W., Sjoquist, Steven E.
• Primary Examiner(s): Cohen, Lee S.
• Assistant Examiner(s): Jastrzab, Jeffrey R.
• Application Number:
  US07/819,193
• Time in Patent Office: 627 Days
• Field of Search: 128/419 D, 128/734, 128/419 PT, 128/697, 128/696, 128/670, 128/908
• US Class Current: 600/510
• CPC Class Codes: A61N 1/3706 Pacemaker parameters stimulation threshold A61N1/371
• CPC Class Codes: A61N 1/3904 External heart defibrillators [EHD]
• CPC Class Codes: A61N 1/3931 Protecting, e.g. back-up systems

Abstract

A defibrillator/monitor (10) employing a motion detection circuit 18 and control and processing circuit (20) that cooperatively detect motion at a patient-electrode interface. In that regard, an impedance measurement circuit (24) produces an output indicative of the impedance of the interface. This output is then processed by a number of filter elements before being analyzed by a motion detection routine (52). The motion detection routine includes subroutines (62 and 64) that compare the impedance against distinct upper and lower limits and then monitor the time at which the signal is above and below the limits. Basically, motion is indicated if the signal undergoes relatively large variations for a short time, or smaller variations for a longer time. A third motion clear subroutine (66) is used to determine when motion is no longer detected. Finally, a similar scheme (102) is employed to quickly restore the various filter elements after saturation.

Claims

1. A method of detecting relative motion between an electrode and a patient, the electrode being coupled to the patient and to a medical instrument, the instrument providing a signal related to the impedance of the electrode/patient interface, said method comprising the steps of:

(a) comparing the signal to a first range of values;

(b) storing a first inside time representative of the time during which the signal is within the first range of values and a first outside time representative of the time during which the signal is outside the first range of values;

(c) setting the first inside and outside times to zero when the first inside time exceeds a first inside time limit; and

(d) producing a motion detection output indicative of relative motion between the electrode and the patient when the first outside time exceeds a first outside time limit.

2. The method of claim 1, further comprising the steps of:

comparing the signal to a second range of values;

storing a second inside time representative of the time during which the signal is within the second range of values and a second outside time representative of the time during which the signal is outside the second range of values;

setting the second inside and outside times to zero when the second inside time exceeds a second inside time limit;

producing a motion detection output representative of relative motion between the electrode and the patient when the second outside time exceeds a second outside time limit.

3. The method of claim 2, further comprising the steps of:

comparing the signal to a third range of values;

storing a third inside time representative of the time during which the signal is within the third range of values and a third outside time representative of the time during which the signal is outside the third range of values;

setting the third inside and outside times equal to zero when the third outside time exceeds a third outside time limit; and

disabling a previously produced motion detection output when the third inside time exceeds a third inside time limit.

4. The method of claim 3, wherein first range of values roughly extends from -0.293 ohm to +0.293 ohm, the first inside time limit is roughly equal to 0.033 second, the first outside time limit is roughly equal to 0.100 second, the second range of values roughly extends from -0.117 ohm to +0.117 ohm, the second inside time limit is roughly equal to 0.333 second, the second outside time limit is roughly equal to 0.333 second, the third range of values roughly extends from -0.117 ohm to +0.117 ohm, the third inside time limit is roughly equal to 1.5 seconds, and the third outside time limit is roughly equal to 0.750 second.

5. A system for use with an instrument in detecting motion between a patient and an electrode, the electrode being couplable to the patient and the instrument, said system comprising:

impedance detection means for producing a signal representative of the impedance between the electrode and the patient;

comparator means for producing a first output indicative of whether the signal is within a first impedance range;

timer means for monitoring the first output to produce a first inside signal representative of an interval of time the signal is inside the first impedance range and a first outside signal representative of an interval of time the signal is outside the first impedance range;

reset means for setting the first inside and outside signals to zero when the first inside signal exceeds a first inside time limit; and

motion detection means for producing a motion detection output indicative of relative motion between the electrode and the patient when the first outside signal ecceeds a first outside time limit.

6. The system of claim 5, wherein:

said comparator means is further for producing a second output indicative of whether the signal is within a second impedance range;

said timer means is further for monitoring the second output to produce a second inside signal representative of an interval of time the signal is inside the second impedance range and a second outside signal representative of an interval of time the signal is outside the second impedance range;

said reset means is further for setting the second inside and outside signals to zero when the second inside signal exceeds a second inside time limit; and

said motion detection means is further for producing a motion detection output indicative of relative motion between the electrode and the patient when the second outside signal exceeds a second outside time limit.

7. The system of claim 6, wherein:

said comparator means is further for producing a third output indicative of whether the signal is within a third impedance range;

said timer means is further for monitoring the third output to produce a third inside signal representative of an interval of time the signal is inside the third impedance range and a third outside signal representative of an interval of time the signal is outside the third impedance range;

said reset means if further for setting the third inside and outside signals to zero when the third outside signal exceeds a third outside time limit; and

further comprising disablement means for disabling a previously produced motion detection output when the third inside signal exceeds a third inside time limit.

8. A limit detection system for use in a medical instrument to analyze a signal that is related to a patient parameter, said limit detection system comprising:

threshold means for comparing the signal to a first range of values;

inside timer means for storing an indication of a first inside time during which the signal is within the first range of values;

inside procedure means for instructing the instrument to initiate a first inside procedure when the first inside time exceeds a first inside time limit;

outside timer means for storing an indication of a first outside time during which the signal is outside the first range of values; and

outside procedure means for instructing the instrument to initiate an procedure when the first outside time exceeds a first outside time limit.

9. The system of claim 8, wherein said threshold means is further for comparing the signal to a second range of values, said inside timer means is further for storing an indication of a second inside time during which the signal is within the second range of values, said inside procedure means is further for instructing the instrument to initiate a second inside procedure when the second inside time exceeds a second inside time limit, said outside timer means is further for storing an indication of a second outside time during which the signal is outside the second range of values, and said outside procedure means is further for instructing the instrument to initiate a second outside procedure when the second outside time exceeds a second outside time limit.

10. The system of claim 9, wherein the signal is representative of the impedance between an electrode, coupled to the instrument, and a patient.

11. The system of claim 10, wherein said inside procedure means comprises reset means for resetting the inside and outside times to zero and wherein said outside procedure means comprises motion detection means for providing a motion detection output to the instrument indicative of relative motion between the electrode and patient.

12. The system of claim 8, wherein the signal is representative of the impedance between an electrode, coupled to the instrument, and a patient.

13. The system of claim 12, wherein said inside procedure means comprises reset means for resetting the inside and outside timers to zero and wherein said outside procedure means comprises fast restore means for providing a fast restore output to the instrument indicative of an undesired disturbance in the signal.

14. The system of claim 8, wherein the signal is representative of an electrocardiographic signal received by the instrument.

15. The system of claim 14, wherein said inside procedure means comprises reset means for resetting the inside and outside timers to zero and wherein said outside procedure means comprises fast restore means for providing a fast restore output to the instrument indicative of an undesired disturbance in the signal.

16. A method of detecting the limits of a physiological signal processed by a medical instrument comprising the steps of:

(a) comparing the signal to a first range of values;

(b) storing an inside time, representative of the time during which the signal is substantially within the range of values, and an outside time, representative of the time during which the signal is substantially outside the range of values;

(c) producing an inside action signal when the inside time exceeds a first inside time limit and an outside action signal when the outside time exceeds a first outside time limit; and

(d) repeating steps (a) through (c) for a second range of values.

17. The method of claim 16, wherein the step of repeating step (c) comprises the step of producing an inside action signal when the inside time exceeds a second inside time limit and an outside action signal when the outside time exceeds a second outside time limit.

18. The method of claim 17, wherein the first and second ranges of values are different, the first and second inside time limits are different, and the first and second outside time limits are different.

19. The method of claim 16, wherein a condition of interest may be associated with the physiological signal and the inside action signal produced during the initial performance of step (c) or the repetition of step (c) is used to detect the condition of interest.

20. The method of claim 16, wherein a condition of interest may be associated with the physiological signal, the inside action signal produced during the initial performance of step (c) is used to detect the presence of the condition of interest, and the inside action signal produced during the repetition of step (c) is used to detect the absence of the condition of interest.

21. A method of restoring a filter circuit used to process a physiological signal to a medical instrument comprising the steps of:

(a) comparing the signal to a first range of values;

(b) storing a first inside time representative of the time during which the signal is within the first range of values and a first outside time representative of the time during which the signal is outside the first range of values;

(c) setting the first inside time and outside times to zero when the first inside time exceeds a first inside time limit;

(d) producing a fast restore output indicative of excessive charging of the filter circuit when the first outside time exceeds a first outside time limit.

22. A method of detecting relative motion between an electrode and a patient and restoring a filter circuit employed in the detection of motion, the electrode being coupled to the patient and to a medical instrument including the filter circuit, the instrument providing a signal related to the impedance of the electrode/patient interface, said method comprising the steps of:

(a) comparing the signal to a first range of values;

(b) storing a first inside time representative of the time during which the signal is within the first range of values and a first outside time representative of the time during which the signal is outside the first range of values;

(c) setting the first inside and outside times to zero when the first inside time exceeds a first inside time limit;

(d) producing a motion detection output indicative of relative motion between the electrode and the patient when the first outside time exceeds a first outside time limit;

(e) comparing the signal to a second range of values;

(f) storing a second inside time representative of the time during which the signal is within the second range of values and a second outside time representative of the time during which the signal is outside the second range of values;

(g) setting the second inside and outside times to zero when the second inside time exceeds a second inside time limit; and

(h) producing a fast restore output indicative of excessive charging of the filter circuit when the second outside time exceeds a second outside time limit.

23. The method of claim 22, further comprising the steps of:

comparing the signal to a third range of values;

storing a third inside time representative of the time during which the signal is within the third range of values and a third outside time representative of the time during which the signal is outside the third range of values;

setting the third inside and outside times to zero when the third inside time exceeds a third inside time limit; and

producing a motion detection output indicative of relative motion between the electrode and the patient when the third outside time exceeds a third outside time limit.