Blood Pressure

Measuring blood pressure in noisy environments

Blood Pressure 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.

Blood Pressure Claims
What is claimed is:

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 transdu