Continuous non-invasive blood pressure monitoring method and apparatus
First Claim
Patent Images
1. A method for monitoring blood pressure, the method comprising:
- a) detecting a first pulse signal at a first location on a subject and detecting a second pulse signal at a second location on the subject;
b) measuring a reference blood pressure P0 and a corresponding time difference T0 between the first and second pulse signals;
c) from the reference blood pressure and corresponding time difference, determining a first plurality of constant parameters in a multi-parameter equation relating blood pressure and the time-difference;
d) monitoring the subject'"'"'s blood pressure by periodically measuring a time difference T between the first and second pulse signals; and
, e) computing an estimated blood pressure, P, from the time difference, T, using the multi-parameter equation and the first plurality of constant parameters wherein the multi-parameter equation is the calculation;
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Abstract
A non-invasive apparatus and method for monitoring the blood pressure of a subject detects a pulse signal at both a first and second location on the subject'"'"'s body. The elapsed time between the arrival of corresponding points of the pulse signal at the first and second locations is determined. Blood pressure is related to the elapsed time by relationships such as:
where a and b are constants dependent upon the nature of the subject and the signal detecting devices. The system can be calibrated by measuring a single pair of reference blood pressure and corresponding elapsed time.
222 Citations
63 Claims
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1. A method for monitoring blood pressure, the method comprising:
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a) detecting a first pulse signal at a first location on a subject and detecting a second pulse signal at a second location on the subject;
b) measuring a reference blood pressure P0 and a corresponding time difference T0 between the first and second pulse signals;
c) from the reference blood pressure and corresponding time difference, determining a first plurality of constant parameters in a multi-parameter equation relating blood pressure and the time-difference;
d) monitoring the subject'"'"'s blood pressure by periodically measuring a time difference T between the first and second pulse signals; and
,e) computing an estimated blood pressure, P, from the time difference, T, using the multi-parameter equation and the first plurality of constant parameters wherein the multi-parameter equation is the calculation;
- View Dependent Claims (2, 3)
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4. A method for monitoring blood pressure, the method comprising:
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a) detecting a first pulse signal at a first location on a subject and detecting a second pulse signal at a second location on the subject;
b) measuring a reference blood pressure P0 and a corresponding time difference T0 between the first and second pulse signals;
c) from the reference blood pressure and corresponding time difference, determining a first plurality of constant parameters in a multi-parameter equation relating blood pressure and the time-difference;
d) monitoring the subject'"'"'s blood pressure by periodically measuring a time difference T between the first and second pulse signals; and
,e) computing an estimated blood pressure, P, from the time difference, T, using the multi-parameter equation and the first plurality of constant parameters wherein the multi-parameter equation comprises a non-linear function which is generally decreasing and concave upward in a manner specified by the constant parameters. - View Dependent Claims (5)
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6. A method for monitoring blood pressure, the method comprising:
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a) detecting a first pulse signal at a first location on a subject and detecting a second pulse signal at a second location on the subject;
b) measuring a reference blood pressure P0 and a corresponding time difference T0 between the first and second pulse signals;
c) from the reference blood pressure and corresponding time difference, determining a first plurality of constant parameters in a multi-parameter equation relating blood pressure and the time-difference;
d) monitoring the subject'"'"'s blood pressure by periodically measuring a time difference T between the first and second pulse signals; and
,e) computing an estimated blood pressure, P, from the time difference, T, using the multi-parameter equation and the first plurality of constant parameters wherein the multi-parameter equation is the calculation;
ti P=α
T−
β
or a mathematical equivalent thereof where α and
β
are constants.
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7. A method for monitoring blood pressure, the method comprising:
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a) detecting a first pulse signal at a first location on a subject and detecting a second pulse signal at a second location on the subject;
b) measuring a reference blood pressure P0 and a corresponding time difference T0 between the first and second pulse signals;
c) from the reference blood pressure and corresponding time difference, determining a first plurality of constant parameters in a multi-parameter equation relating blood pressure and the time-difference;
d) monitoring the subject'"'"'s blood pressure by periodically measuring a time difference T between the first and second pulse signals; and
,e) computing an estimated blood pressure, P, from the time difference, T, using the multi-parameter equation and the first plurality of constant parameters wherein the multi-parameter equation is the calculation;
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8. A method for monitoring blood pressure, the method comprising:
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a) detecting a first pulse signal at a first location on a subject and detecting a second pulse signal at a second location on the subject;
b) measuring a reference blood pressure P0 and a corresponding time difference T0 between the first and second pulse signals;
c) from the reference blood pressure and corresponding time difference, determining a first plurality of constant parameters in a multi-parameter equation relating blood pressure and the time-difference;
d) monitoring the subject'"'"'s blood pressure by periodically measuring a time difference T between the first and second pulse signals; and
,e) computing an estimated blood pressure, P, from the time difference, T, using the multi-parameter equation and the first plurality of constant parameters wherein the blood pressure is a systolic blood pressure.
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9. A method for monitoring blood pressure, the method comprising:
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a) detecting a first pulse signal at a first location on a subject and detecting a second pulse signal at a second location on the subject;
b) measuring a reference blood pressure P0 and a corresponding time difference T0 between the first and second pulse signals;
c) from the reference blood pressure and corresponding time difference, determining a first plurality of constant parameters in a multi-parameter equation relating blood pressure and the time-difference;
d) monitoring the subject'"'"'s blood pressure by periodically measuring a time difference T between the first and second pulse signals; and
,e) computing an estimated blood pressure, P, from the time difference, T, using the multi-parameter equation and the first plurality of constant parameters wherein the method comprises measuring a systolic blood pressure of the subject wherein measuring the time difference T comprises measuring a first time difference Ts for portions of the first and second signals which do not include at least some diastolic portions of the signals. - View Dependent Claims (10, 11, 12, 13, 14)
the method comprises monitoring the subject'"'"'s diastolic blood pressure by periodically measuring the second time difference TD and, computing an estimated diastolic blood pressure, PD, from the time difference, TD, using the multi-parameter equation and the second plurality of constant parameters.
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12. The method of claim 9 wherein measuring the first time difference comprises maximizing a cross-correlation between the first and second pulse signals.
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13. The method of claim 12 wherein, in measuring the first time difference, portions of the first and second pulse signals below a first threshold are not considered.
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14. The method of claim 13 wherein the threshold for the first pulse signal is an average value of the first pulse signal and the threshold for the second pulse signal is an average value of the second pulse signal.
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15. A method for estimating a blood pressure of a subject, the method comprising:
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a) detecting a first pulse signal at a first location;
b) detecting a second pulse signal at a second location;
c) determining an elapsed times, T, between the arrival of corresponding points of the first and second pulse signals; and
,d) computing an estimated blood pressure, P, from the elapsed time by performing the calculation;
- View Dependent Claims (16, 17, 18, 19, 20)
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21. A method for estimating the blood pressure, P, of a subject, the method comprising:
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a) detecting a first pulse signal at a first location on the subject;
b) detecting a second pulse signal at a second location on the subject;
c) performing a calibration by measuring the subject'"'"'s blood pressure P0 and measuring a corresponding elapsed time, T0, between the arrival of corresponding points of the first and second pulse signals;
d) subsequently monitoring the subject'"'"'s blood pressure by determining an elapsed time, T, between the arrival of corresponding points of the first and second pulse signals; and
,e) calculating an estimated blood pressure, P, based on the value;
where c1 and a2 are constants.- View Dependent Claims (22, 23, 24, 25, 26, 27)
or a substantially mathematically equivalent computation.
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23. The method of claim 22 wherein c1 is about 85.41, and c2 is about −
- 4.73 for systolic pressure measurements.
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24. The method of claim 23 wherein c1 is about 49.36 and c2 is about −
- 4.3 for diastolic pressure measurements.
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25. The method of claim 23 wherein c1 is in the range of 85±
- 10 and c2 is in the range of −
4.7±
1 for systolic pressure measurements.
- 10 and c2 is in the range of −
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26. The method of claim 23 wherein c1 is in the range of 50±
- 10 and c2 is in the range of −
4.3±
1 for diastolic pressure measurements.
- 10 and c2 is in the range of −
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27. The method of claim 23 where c1 and c2 are derived by:
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for several subjects, at each of two or more times, measuring a reference blood pressure value P0 and a corresponding elapsed time, T0, between corresponding points of the first and second pulse signals;
for each of the subjects determining best fit values for a and b such that;
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28. A method for estimating the blood pressure, P, of a subject, the method comprising:
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a) detecting a first pulse signal at a first location on the subject;
b) detecting a second pulse signal at a second location on the subject;
c) performing a calibration by measuring the subject'"'"'s blood pressure P0 and measuring a corresponding elapsed time, T0, between the arrival of corresponding points of the first and second pulse signals;
d) subsequently monitoring the subject'"'"'s blood pressure by determining an elapsed time, T, between the arrival of corresponding points of the first and second pulse signals; and
,f) calculating and estimated blood pressure, P, substantially according to the equation;
- View Dependent Claims (29, 30, 31, 32, 33)
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34. Apparatus for estimating a blood pressure of a subject, the apparatus comprising:
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a) a computer processor;
b) an input for receiving a first signal corresponding to a pulse signal detected at a first location;
c) an input for receiving a second signal corresponding to the pulse signal detected at a second location;
d) a program store containing computer software comprising instructions which, when run on the processor cause the processor to measure an elapsed time, T, between corresponding points on the first and second signals and compute an estimated blood pressure, P, from the elapsed time by performing the calculation;
- View Dependent Claims (35, 36, 37, 38)
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39. Apparatus for estimating a blood pressure of a subject, the apparatus comprising:
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a) signal detection means for detecting first and second pulse signals;
b) correlation means for determining an elapsed time, T, between the first and second pulse signals;
c) computation means for computing an estimated blood pressure, P, from the elapsed time according to a non-linear function which is generally decreasing and concave upward in a manner specified by two or more settable parameters; and
,d) calibration means for receiving a reference blood pressure and associating the reference blood pressure with an elapsed time determined by the correlation means; and
,e) means responsive to the calibration means for establishing values for the two or more settable parameters from the reference blood pressure and elapsed time. - View Dependent Claims (40, 41, 42, 43, 44, 45, 46, 47)
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42. The apparatus of claim 39 wherein the correlation means determines separate first and second time differences TS and TD respectively from higher and lower portions of the first and second pulse signals respectively.
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43. The apparatus of claim 42 wherein the computation means comprises diastolic blood pressure computation means for computing a diastolic blood pressure from the first time difference and systolic blood pressure computation means for computing a systolic blood pressure from the second time difference.
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44. The apparatus of claim 39 wherein the correlation means comprises a buffer for holding a segment of the first pulse signal, a buffer for holding a segment of the second pulse signal and a processor executing instructions which cause the processor to determine a time difference for which a cross correlation between the segment of the first pulse signal and the segment of the second pulse signal is maximized.
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45. The apparatus of claim 44 wherein the correlation means determines separate first and second time differences TS and TD respectively from higher and lower portions of the first and second pulse signals respectively.
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46. The apparatus of claim 45 wherein the correlation means comprises means for computing an average value of each of the first and second pulse signals and the higher portions comprise portions having a value in excess of the average value.
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47. The apparatus of claim 44 wherein the correlation means comprises means for creating from the first and second pulse signals a first set of modified signals p1(t) and p2(t) which include the peaks of the first and second pulse signals but do not include valleys of the first and second pulse signals and the correlation means determines a first time difference TS by determining a time shift which yields a maximum correlation between signals of the first set of modified signals.
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48. A program product comprising a medium bearing computer-readable signals, the signals containing instructions which, when executed on a computer processor, cause the computer processor to perform a method for monitoring blood pressure, the method comprising:
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a) detecting a first pulse signal at a first location on a subject and detecting a second pulse signal at a second location on the subject;
b) measuring a reference blood pressure P0 and a corresponding time difference T0 between the first and second pulse signals;
c) from the reference blood pressure and corresponding time difference, determining a first plurality of constant parameters in a multi-parameter equation relating blood pressure and the time-difference;
d) monitoring the subject'"'"'s blood pressure by periodically measuring a time difference T between the first and second pulse signals; and
,e) computing an estimated blood pressure, P, from the time difference, T, using the multi-parameter equation and the first plurality of constant parameters.
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49. A method for obtaining a value representing a blood pressure of a subject, the method comprising:
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measuring a reference blood pressure P0 and determining a corresponding reference time difference, T0 by at least;
receiving a first pulse signal detected at a first location on the subject;
receiving a second pulse signal detected at a second location on the subject; and
,determining the reference time difference, T0, by measuring a time shift between corresponding points of the first and second pulse signals;
based upon the reference blood pressure and the reference time difference, obtaining a non-linear function relating blood pressure and time difference for the subject; and
,at one or more subsequent times, computing an estimated blood pressure, P, by at least;
at the one or more subsequent times, determining a time difference, T, between corresponding points of the first and second pulse signals and computing the non-linear function of the time difference wherein obtaining the non-linear function comprises determining at least two parameters of the non-linear function. - View Dependent Claims (50, 51, 52, 53, 54, 55, 56, 57, 58, 59)
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55. The method of claim 54 wherein obtaining the second parameter comprises performing the calculation:
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56. The method of claim 50 wherein the predetermined function is a function obtained by:
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collecting multiple pairs of reference time difference and reference blood pressure for each of a plurality of reference subjects;
for each of the plurality of reference subjects fitting the non-linear function to the multiple pairs of reference time difference and reference blood pressure to obtain values for the first and second parameters for each of the plurality of reference subjects; and
,fitting a suitable curve to obtain the predetermined function.
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57. The method of claim 56 wherein the suitable curve comprises a linear trend line.
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58. The method of claim 57 wherein the plurality of reference subjects is selected by picking reference subjects for whom a measure of fit between the non-linear function and the multiple pairs of reference time difference and reference blood pressure exceeds a threshold.
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59. The method of claim 58 wherein the measure of fit comprises an R-squared value.
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60. A method for obtaining a value representing a blood pressure of a subject, the method comprising:
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measuring a reference blood pressure P0 and determining a corresponding reference time difference, T0 by at least;
receiving a first pulse signal detected at a first location on the subject;
receiving a second pulse signal detected at a second location on the subject; and
,determining the reference time difference, T0, by measuring a time shift between corresponding points of the first and second pulse signals;
based upon the reference blood pressure and the reference time difference, obtaining a non-linear function relating blood pressure and time difference for the subject; and
,at one or more subsequent times, computing an estimated blood pressure, P, by at least;
at the one or more subsequent times, determining a time difference, T, between corresponding points of the first and second pulse signals and computing the non-linear function of the time difference wherein the non-linear function comprises a logarithmic function of T.
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61. A method for obtaining a value representing a blood pressure of a subject, the method comprising:
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measuring a reference blood pressure P0 and determining a corresponding reference time difference, T0 by at least;
receiving a first pulse signal detected at a first location on the subject;
receiving a second pulse signal detected at a second location on the subject; and
,determining the reference time difference, T0, by measuring a time shift between corresponding points of the first and second pulse signals;
based upon the reference blood pressure and the reference time difference, obtaining a non-linear function relating blood pressure and time difference for the subject; and
,at one or more subsequent times, computing an estimated blood pressure, P, by at least;
at the one or more subsequent times, determining a time difference, T, between corresponding points of the first and second pulse signals and computing the non-linear function of the time difference wherein the value representing a blood pressure of a subject represents a systolic blood pressure of the subject and the corresponding points on the first and second signals are in parts of the first and second signals corresponding to a systolic portion of the subject'"'"'s pulse.
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62. A method for obtaining a value representing a blood pressure of a subject, the method comprising:
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measuring a reference blood pressure P0 and determining a corresponding reference time difference, T0 by at least;
receiving a first pulse signal detected at a first location on the subject;
receiving a second pulse signal detected at a second location on the subject; and
,determining the reference time difference, T0, by measuring a time shift between corresponding points of the first and second pulse signals;
based upon the reference blood pressure and the reference time difference, obtaining a non-linear function relating blood pressure and time difference for the subject; and
,at one or more subsequent times, computing an estimated blood pressure, P, by at least;
at the one or more subsequent times, determining a time difference, T, between corresponding points of the first and second pulse signals and computing the non-linear function of the time difference wherein the non-linear function comprises a logarithmic function of T.
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63. A method for obtaining a value representing a blood pressure of a subject, the method comprising:
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measuring a reference blood pressure P0 and determining a corresponding reference time difference, T0 by at least;
receiving a first pulse signal detected at a first location on the subject;
receiving a second pulse signal detected at a second location on the subject; and
,determining the reference time difference, T0, by measuring a time shift between corresponding points of the first and second pulse signals;
based upon the reference blood pressure and the reference time difference, obtaining a non-linear function relating blood pressure and time difference for the subject; and
,at one or more subsequent times, computing an estimated blood pressure, P, by at least;
at the one or more subsequent times, determining a time difference, T, between corresponding points of the first and second pulse signals and computing the non-linear function of the time difference wherein the value representing a blood pressure of a subject represents a systolic blood pressure of the subject and the corresponding points on the first and second signals are in parts of the first and second signals corresponding to a systolic portion of the subject'"'"'s pulse.
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Specification