Measuring blood pressure in noisy environments

• US 6,258,037 B1
• Filed: 06/25/1999
• Issued: 07/10/2001
• Est. Priority Date: 06/25/1999
• Status: Expired due to Fees

• Current Assignee: Cardiodyne, Inc. (Integra LifeSciences Holdings Corporation)
• Original Assignee: Cardiodyne, Inc. (Integra LifeSciences Holdings Corporation)
• Inventors: Dowling, Neal B. Jr.
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US09/344,702
• Time in Patent Office: 746 Days
• Field of Search: 600/485, 600/490, 600/493-6, 600/500
• US Class Current: 600/493
• CPC Class Codes: A61B 5/02208 using the Korotkoff method
• CPC Class Codes: A61B 5/7285 for synchronising or triggering a physiological measurement or image acquisition with a physiological event or waveform, e.g. an ECG signal A61B6/5205, A61B6/541, A61B8/5207, A61B8/543 take precedence
• CPC Class Codes: A61B 7/045 Detection of Korotkoff sounds A61B5/0225 takes precedence; measuring blood pressure A61B5/021

Abstract

Several techniques are provided for aiding in the discrimination of detected biological signals indicative of blood pressure from detected signals not indicative of blood pressure (e.g., noise). In one technique, mixed signals which include biological signals indicative of blood pressure and noise signals not indicative of blood pressure are detected during time periods, and are evaluated over a plurality of the time periods to aid in discriminating the biological signals from the noise signals. This enhances the signal-to-noise ratio of the biological signals. In a related technique, the mixed signals are analyzed in different ways based on whether the noise level exceeds a threshold to discriminate the biological signals from the noise signals. Still another technique includes determining whether a candidate blood pressure signal should be used to measure blood pressure based on whether it exceeds a plurality of different thresholds. In another technique, a portion of the time periods in which the mixed signals are analyzed is selected based on levels of the biological signals in the mixed signals and times during a cardiac cycle intervals during which they are detected.

Claims

1. A method for use in measuring blood pressure, comprising

detecting mixed signals during time periods, the mixed signals including biological signals indicative of blood pressure and noise signals not indicative of blood pressure,

evaluating the mixed signals over a plurality of the time periods to aid in discriminating the biological signals from the noise signals,

the evaluating comprising assembling the mixed signals detected at corresponding times during the plurality and analyzing the assembled mixed signals to aid in discriminating the biological signals from the noise signals,

the analyzing comprising developing a candidate blood pressure signal based on the biological signals indicative of blood pressure in the assembled mixed signals, and determining whether the candidate blood pressure signal should be used to measure blood pressure,

the determining comprising determining whether the candidate blood pressure signal should be used to measure blood pressure based on whether it exceeds a plurality of combinations of different thresholds, and

assigning a score to the candidate blood pressure signal that indicates a likelihood that the candidate blood pressure signal is valid blood pressure signal, the score being based on which thresholds are exceeded.

2. The method of claim 1 wherein the assembling includes accumulating the mixed signals detected at the corresponding times during the plurality of time periods.

3. The method of claim 1 wherein the time periods are cardiac cycle intervals.

4. The method of claim 3 wherein the assembling includes accumulating samples of the mixed signals that are taken at corresponding time delays after a start of each of the cardiac cycle intervals.

5. The method of claim 4 further comprising detecting the start of each cardiac cycle interval based on an occurrence of a timing signal that is synchronous with the cardiac cycle.

6. The method of claim 5 wherein the timing signal is an R-wave signal.

7. The method of claim 1 wherein the determining comprises determining that the candidate blood pressure signal should be used to measure blood pressure if it exceeds a threshold.

8. The method of claim 1 further comprising measuring blood pressure based on the scores of the candidate blood pressure signals.

9. The method of claim 1 wherein the plurality of thresholds include a history threshold, and further comprising developing the history threshold based on previously detected biological signals indicative of blood pressure in the assembled mixed signals that have exceeded the threshold.

10. The method of claim 1 wherein the plurality of thresholds include a noise threshold, and further comprising developing the noise threshold based on the noise signals not indicative of blood pressure in the assembled mixed signals.

11. The method of claim 1 further comprising developing the candidate blood pressure signal from the biological signals indicative of blood pressure in the assembled mixed signals only during a selected portion of one of the time periods.

12. The method of claim 11 wherein the time periods are cardiac cycle intervals, and further comprising determining the selected portion based on levels of the biological signals indicative of blood pressure in the assembled mixed signals and times during the cardiac cycle intervals during which they are detected.

13. The method of claim 1 wherein the detecting includes detecting the mixed signals with a plurality of transducers on a blood pressure cuff, and further comprising assembling the mixed signals detected at corresponding times during the plurality of time periods by each of the transducers, and analyzing the assembled mixed signals to aid in discriminating the biological signals from the noise signals.

14. The method of claim 13 further comprising combining the assembled mixed signals from each of the transducers with each other to develop a candidate blood pressure signal in which the biological signals are reinforced and the noise signals are attenuated.

15. The method of claim 14 wherein the combining includes subtracting the assembled mixed signals detected by one of the transducers from the assembled mixed signals detected by another one of the transducers.

16. The method of claim 14 further comprising determining whether the candidate blood pressure signal should be used to measure blood pressure based on whether it exceeds a plurality of combinations of different thresholds.

17. The method of claim 16 further comprising assigning a score to the candidate blood pressure signal that indicates a likelihood that the candidate blood pressure signal is a valid blood pressure signal, the score being based on which thresholds are exceeded.

18. The method of claim 16 further comprising measuring blood pressure based on the scores of the candidate blood pressure signals.

19. The method of claim 16 wherein one of the plurality of thresholds includes a history threshold, and further comprising developing the history threshold based on previously determined candidate blood pressure signals.

20. The method of claim 16 wherein one of the thresholds includes a noise threshold, and further comprising developing the noise threshold based on the noise signals detected during the time periods.

21. The method of claim 20 further comprising developing the noise threshold by combining the assembled mixed signals from the plurality of transducers so as to reinforce the noise signals and attenuate the biological signals.

22. The method of claim 21 wherein the combining to develop the noise threshold includes summing the assembled mixed signals from the plurality of transducers.

23. Apparatus for use in a blood pressure measuring device, comprising

at least one transducer for detecting mixed signals during time periods, the mixed signals including biological signals indicative of blood pressure and noise signals not indicative of blood pressure, and

processing circuitry for evaluating the mixed signals over a plurality of the time periods to aid in discriminating the biological signals from the noise signals, the processing circuitry being adapted to:

develop a candidate blood pressure signal from the biological signals indicative of blood pressure in the assembled mixed signals, and determine whether the candidate blood pressure signal should be used to measure blood pressure,

determine whether the candidate blood pressure signal should be used to measure blood pressure based on whether it exceeds a plurality of different thresholds, and

assign a score to the candidate blood pressure signal that indicates a likelihood that the candidate blood pressure signal is a valid blood pressure signal, the score being based on which thresholds are exceeded.

24. The apparatus of claim 23 wherein the processing circuitry comprises

circuitry for assembling the mixed signals detected at corresponding times during the plurality of time periods, and

a processor for analyzing the assembled mixed signals to aid in discriminating the biological signals from the noise signals.

25. The apparatus of claim 24 wherein the circuitry for assembling includes an accumulator for accumulating the mixed signals detected at the corresponding times during the plurality of time periods.

26. The apparatus of claim 25 wherein the apparatus includes a plurality of transducers each of which detects the mixed signals during the time periods, and further comprising

an accumulator associated with each of the transducers for accumulating the mixed signals detected thereby at the corresponding times during the plurality of time periods,

the processor analyzing the accumulated mixed signals from the accumulators to aid in discriminating the biological signals from the noise signals.

27. The apparatus of claim 24 wherein the time periods are cardiac cycle intervals.

28. The apparatus of claim 27 wherein the accumulator is controlled to accumulate samples of the mixed signals that are taken at corresponding time delays after a start of each of the cardiac cycle intervals.

29. The apparatus of claim 28 further comprising circuitry for detecting the start of each cardiac cycle interval based on an occurrence of a timing signal that is synchronous with the cardiac cycle.

30. The apparatus of claim 29 wherein the timing signal is an R-wave signal.

31. The apparatus of claim 23 wherein the processing circuitry is further adapted to determine that the candidate blood pressure signal should be used to measure blood pressure if it exceeds the threshold.

32. The apparatus of claim 23 wherein the processing circuitry is adapted to measure blood pressure based on the scores of the candidate blood pressure signals.

33. The apparatus of claim 23 wherein the plurality of thresholds include a history threshold, the processing circuitry being adapted to develop the history threshold based on previously detected biological signals indicative of blood pressure in the assembled mixed signals that have exceeded the threshold.

34. The apparatus of claim 23 wherein the plurality of thresholds include a noise threshold, the processing circuitry being adapted to develop the noise threshold based on the noise signals not indicative of blood pressure in the assembled mixed signals.

35. The apparatus of claim 23 wherein the processing circuitry is adapted to develop the candidate blood pressure signal from the biological signals indicative of blood pressure in the assembled mixed signals only during a selected portion of one of the time periods.

36. The apparatus of claim 35 wherein the time periods are cardiac cycle intervals, the processing circuitry being adapted to determine the selected portion based on levels of the biological signals indicative of blood pressure in the assembled mixed signals and times during the cardiac cycle intervals during which they are detected.

37. A method for use in measuring blood pressure, comprising

detecting mixed signals that include biological signals indicative of blood pressure and noise signals not indicative of blood pressure,

determining if a noise level exceeds a threshold, and

analyzing the mixed signals in a first way if the noise level does not exceed the threshold to discriminate the biological signals from the noise signals, and analyzing the mixed signals in a second, different way if the noise level exceeds the threshold to discriminate the biological signals from the noise signals,

the detecting including detecting the mixed signals during time periods, the first way of analyzing comprising evaluating the mixed signals in each of the time periods individually, and the second way of analyzing comprising evaluating the mixed signals over a plurality of the time periods.

40. The method of claim 37 or 38 wherein the determining is based on the detected noise signals not indicative of blood pressure in the mixed signals.

41. The method of claim 37 or 38 further comprising performing the analyzing on the mixed signals detected during cardiac cycle intervals, and performing the determining based on the mixed signals received outside of the cardiac cycle intervals.

38. A method for use in measuring blood pressure, comprising

detecting mixed signals that include biological signals indicative of blood pressure and noise signals not indicative of blood pressure,

determining if a noise level exceeds a threshold, and

analyzing the mixed signals in a first way if the noise level does not exceed the threshold to discriminate the biological signals from the noise signals, and analyzing the mixed signals in a second, different way if the noise level exceeds the threshold to discriminate the biological signals from the noise signals,

the detecting including detecting the mixed signals during time periods, the second way of analyzing comprising

assembling the mixed signals detected at corresponding times during the time periods, and

analyzing the assembled mixed signals to discriminate the biological signals from the noise signals.

39. The method of claim 38 wherein the time periods are cardiac cycle intervals and the assembling includes accumulating samples of the mixed signals that are taken at corresponding time delays after a start of each of the cardiac cycle intervals.

42. A method for use in measuring blood pressure, comprising

detecting mixed signals which include biological signals indicative of blood pressure and noise signals indicative of blood pressure,

developing a candidate blood pressure signal based on the biological signals indicative of blood pressure in the mixed signals,

determining whether the candidate blood pressure signal should be used to measure blood pressure based on whether it exceeds a plurality of combinations of different thresholds, and

assigning a score to the candidate blood pressure signal that indicates a likelihood that the candidate blood pressure signal is a valid blood pressure signal, the score being based on which thresholds are exceeded.

43. The method of claim 42 further comprising measuring blood pressure based on the scores of the candidate blood pressure signals.

44. The method of claim 42 wherein the plurality of thresholds include a history threshold, and further comprising developing the history threshold based on previously detected biological signals indicative of blood pressure in the mixed signals that have exceeded the threshold.

45. The method of claim 42 wherein the plurality of thresholds include a noise threshold, and further comprising developing the noise threshold based on the noise signals not indicative of blood pressure in the mixed signals.

46. A method for use in measuring blood pressure, comprising

detecting mixed signals during time periods, the mixed signals including biological signals indicative of blood pressure and noise signals not indicative of blood pressure,

selecting a portion of the time periods based on levels of the biological signals indicative of blood pressure in the mixed signals and times during a cardiac cycle intervals during which they are detected, the selecting comprising

designating a nominal time from initiation of a cardiac cycle interval based on a weighted average of times during the cardiac cycle at which the biological signals indicative of blood pressure are detected and levels of said biological signals,

starting the portion of the time period at a first time prior to the nominal time, and

ending the portion of the time period at a second time after the nominal time, and

analyzing the biological signals indicative of blood pressure in the mixed signals only during the selected portion of the time periods to develop a candidate blood pressure signal.

47. The method of claim 46 further comprising selecting the nominal time differently according to whether systolic or diastolic pressure is being measured.

48. The method of claim 46 further comprising changing the first time and the second time in accordance with changes in heart rate.

49. The method of claim 46 further comprising determining whether the candidate blood pressure signal should be used to measure blood pressure based on the analyzing of the biological signals indicative of blood pressure in the mixed signals during the selected portion of the time periods.