Measuring systolic blood pressure by photoplethysmography

• US 20060074322A1
• Filed: 09/30/2004
• Published: 04/06/2006
• Est. Priority Date: 09/30/2004
• Status: Active Grant

• Current Assignee: Jerusalem College Of Technology
• Original Assignee: Jerusalem College Of Technology
• Inventors: Nitzan, Meir
• Granted Patent: US 7,544,168 B2
• Time in Patent Office: Days
• US Class Current: 600/485
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

The present invention relates to cuff-based method for the measurement of systolic blood pressure (SBP) by measuring photoplethysmographic (PPG) signals in peripheral blood vessels distal to the cuff and to a method for cuffless measurement of SBP by analyzing PPG signals in peripheral blood vessels, after suitable calibration by the cuff-based PPG method for the measurement of SBP.

Claims

1. An apparatus for successively assessing arterial blood pressure of a person comprising:

a photoplethysmographic (PPG) sensor, which measures pulses of arterial blood volume change induced by heart beat, being attached to the skin in a first peripheral site;

a second sensor which measures pulses of a second hemodynamic parameter which relate to the heart beat and which detects the arrival time of the said second hemodynamic parameter at different time than the said PPG sensor;

a first electronic means with algorithm for deriving from the PPG pulses and from the second hemodynamic parameter a set of parameters which include the average over 4-12 pulses of the following parameters;

AM/BL, the time delay (TD) between the pulse in the first peripheral site and the pulse in the second peripheral site, and heart period P, where the group of 4-12 pulses, which is used for the determination of the average value of P, is lagged by 4-6 pulses relative to the group used for the determination of the average value of AM/BL.

a cuff-based blood-pressure measuring device which measures, by inflating and slowly deflating the cuff, the systolic blood pressure (SBP) of the person;

a second electronic means which stores the data of SBP and the said PPG parameters obtained in each of at least four examinations, and further develops relationship between SBP and the said PPG parameters; and

a third electronic means which stores data of the said PPG parameters obtained in another examination and by using the said relationship between SBP and the said PPG parameters derives SBP for the time of said another examination.

3. An apparatus as in claim 1, wherein the said second hemodynamic parameter is PPG.

4. An apparatus as in claim 1, wherein the same 4-12 pulses are used for the determination of the average value of AM/BL and TD.

5. An apparatus as in claim 1, wherein different groups of 4-12 pulses are used for the determination of the average value of AM/BL and TD.

6. An apparatus as in claim 1, wherein the group of 4-12 pulses, which is used for the determination of the average value of AM/BL, is lagged by 2-5 pulses relative to the group used for the determination of the average value of TD.

7. An apparatus as in claim 1, wherein the relationship between SBP and the PPG parameters is linear relationship:

SBP=a ₀ +a ₁ AM/BL+a ₂ TD+a ₃ P,

where a₀-a₃ are constants for each person, but are different for different persons.

8. An apparatus as in claim 7, wherein at least one of the coefficients a₀-a₃ takes one value if P increases when AM/BL increases, and different value if P decreases when AM/BL increases.

18. An apparatus as in claim 1, wherein the said first electronic means also includes an algorithm for deriving from the PPG pulses additional set of parameters which include the average over 4-12 pulses of at least one of the following parameters:

the PPG amplitude AM, the PPG baseline BL, maximal derivative MxDr, MxDr/AM, duration time of systolic increase, duration time of systolic increase up to MxDr, the average value of the respiratory period, the maximal change of AM/BL due to respiration and the maximal change of P due to respiration. The values of the said at least one of the parameters are used in the calibration process and for determining the change in its value in the monitoring, together with the changes in AM/BL, P and TD, for the evaluation of SBP.

19. An apparatus as in claim 1, wherein the said first electronic means also derives at least one of the following parameters:

body temperature, skin temperature and room temperature. The values of the said at least one of the parameters are used in the calibration process and for determining the change in its value in the monitoring, together with the changes in AM/BL, P and TD, for the evaluation of SBP.

20. An apparatus as in claim 18, wherein the group of 4-12 pulses, which is used for the determination of the average value of the PPG baseline BL, is lagged by 5-8 pulses relative to the group used for the determination of the average value of AM/BL.

21. An apparatus as in claim 1, wherein the measurement of P is from minimum to minimum

22. An apparatus as in claim 1, wherein the measurement of P is from time of minimum +0.1 AM to time of minimum +0.1 AM.

23. An apparatus as in claim 1, wherein the measurement of TD is from minimum to minimum

24. An apparatus as in claim 1, wherein the measurement of TD is from time of minimum +0.1 AM to time of minimum +0.1 AM.

25. An apparatus as in claim 1, wherein the finger PPG signal is measured by a sensor, comprised of at least one light source and at least one detector, embedded in a ring like device, which is connected to another ring, so that the two rings are put on two adjacent fingers.

26. An apparatus as in claim 1, wherein the said at least four examinations mentioned in claims 1 and 2 for simultaneous measurements of SBP, obtained by cuff-based method and the PPG parameters, are performed in resting sitting position.

27. An apparatus as in claim 1, wherein the said at least four examinations for simultaneous measurements of SBP, obtained by cuff-based method and the PPG parameters, are performed in resting sitting position and after physiological maneuvers, in which the SBP values is expected to be different than resting SBP value.

28. An apparatus as in claim 27, wherein the said physiological maneuvers, in which the SBP values is expected to be different than resting SBP value, include:

standing, deep slow breathing, caffeine ingestion, mental stress and handgrip maneuver.

2. An apparatus for successively assessing arterial blood pressure of a person comprising:

a photoplethysmographic (PPG) sensor, which measures pulses of arterial blood volume change induced by heart beat, being attached to the skin in a first peripheral site;

a second sensor which measures pulses of a second hemodynamic parameter which relate to the heart beat and which detects the arrival time of the said second hemodynamic parameter at different time than the said PPG sensor;

a first electronic means with algorithm for deriving from the PPG pulses and from the second hemodynamic parameter a set of parameters which include the average over 4-15 pulses of the following parameters;

AM/BL and the time delay (TD) between the pulse in the first peripheral site and the pulse in the second peripheral site;

an automatic cuff-based blood-pressure measuring device which measures at least three times the systolic blood pressure (SBP) of the person, by inflating the cuff to air pressure slightly above SBP value and slowly deflating the cuff, and simultaneously measuring the light intensity in the photodetector of a PPG probe located distal to the middle of the cuff, in order to automatically detect the disappearance of the PPG signal during the said inflating the cuff to air pressure slightly above SBP value and the reappearance of the PPG signal during the said slowly deflating the cuff;

a second electronic means which stores the data of SBP and the said PPG parameters obtained in each of at least four examinations, and further develops relationship between SBP and the said PPG parameters;

a third electronic means which stores data of the said PPG parameters obtained in another examination and by using the said relationship between SBP and the said PPG parameters derives SBP for the time of said another examination.

9. An apparatus as in claim 2, wherein the automatic detection of the disappearance of the PPG signal during the inflation periods and the reappearance of the PPG signal during the deflation periods is done by division into segments of the output of the distal-to-the-cuff detector, each segment is expected to include full PPG pulse if PPG pulse appears at the corresponding time, and calculation of two parameters characterizing PPG pulses in each segment:

a pulse pattern parameter and the correlation of the signal in each segment with the signal in the neighboring segment.

10. An apparatus as in claim 9, wherein the said time segments of the detector output distal to the cuff, each of which is expected to include full PPG pulse if PPG pulse appears at the corresponding time, are determined through the corresponding segments in the PPG signal in the other hand, taken from minimum point t_MNF (the time point in which the systolic increase of the PPG pulse starts) to next minimum point, where time-points of the minimum of the PPG signal distal to the cuff are determined in sections with delay relative to the time-points t_MNF of the minimum points of the PPG pulses in the free hand.

11. An apparatus as in claim 10, wherein the said sections are chosen from t_MNF+50 ms to t_MNF+120 ms.

12. An apparatus as in claim 9, wherein the said time segments of the detector output distal to the cuff, each of which is expected to include full PPG pulse if PPG pulse appears at the corresponding time, are determined through the corresponding segments in the PPG signal in the other hand, taken from time-point of maximum derivative (t_DMXF) to next time-point of maximum derivative, where time-points of the maximum derivative of the PPG signal distal to the cuff are determined in sections with delay relative to the time-points t_DMXF of the maximum derivative points of the PPG pulses in the free hand.

13. An apparatus as in claim 12, wherein the said sections are chosen from t_DMXF+50 ms to t_DMXF+120 ms.

14. An apparatus as in claim 9, wherein the said pulse pattern is determined by subtracting the line connecting the point of the maximum derivative of the pulse to the next maximum derivative point from the output of the PPG sensor distal to the cuff, and calculating the integral of the difference between the said output and the said line for the first half (INT1) and the second half (INT2) of the segment, and the difference between the integral values for the two halves (INT1−

INT2) is taken as pulse pattern parameter.

15. An apparatus as in claim 9, wherein the correlation of the signal in each segment with the signal in the neighboring segment is performed by eliminating sampling points from the longer segment if the two segments are not equal.

16. An apparatus as in claim 9, wherein the average value of PPP for the hand distal to the hand before the inflation (PPP_IN) is calculated, and the first PPG pulse is taken as the first of seven consecutive segments in which at least five segments have correlation coefficient value higher than predetermined specific value, and PPP value higher than predetermined specific fraction of PPP_IN, provided that the said first pulse have correlation coefficient value higher than that said predetermined specific value, and PPP value higher than that said predetermined specific fraction of PPP_IN.

17. An apparatus as in claim 16, wherein the said predetermined specific fraction of the correlation coefficient is in the region of 0.65-0.85, and the said predetermined specific fraction of PPP_IN is in the region of 1-10% of PPP_IN.

29. An automatic cuff-based blood-pressure measuring device which measures at least three times the systolic blood pressure (SBP) of the person, by means of inflation of the cuff to air pressure slightly above SBP value and subsequent slow deflation the cuff, and simultaneously measuring the light intensity in the photodetector of a PPG probe located distal to the middle of the cuff, in order to automatically detect the disappearance of the PPG signal during the said inflating the cuff to air pressure slightly above SBP value and the reappearance of the PPG signal during the said slowly deflating the cuff;

30. A device as in claim 29, wherein the said automatic detection of the disappearance of the PPG signal during the inflation periods and the reappearance of the PPG signal during the deflation periods is done by division into segments of the output of the distal-to-the-cuff detector, each segment is expected to include full PPG pulse if PPG pulse appears at the corresponding time, and calculation of two parameters characterizing PPG pulses in each segment:

a pulse pattern parameter and the correlation of the signal in each segment with the signal in the neighboring segment.

31. A device as in claim 30, wherein the said time segments of the detector output distal to the cuff, each of which is expected to include full PPG pulse if PPG pulse appears at the corresponding time, are determined through the corresponding segments in the PPG signal in the other hand, taken from minimum point t_MNF (the time point in which the systolic increase of the PPG pulse starts) to next minimum point, where time-points of the minimum of the PPG signal distal to the cuff are determined in sections with delay relative to the time-points t_MNF of the minimum points of the PPG pulses in the free hand.

32. A device as in claim 31, wherein the said sections are chosen from t_MNF+50 ms to t_MNF+120 ms.

33. A device as in claim 32, wherein the said time segments of the detector output distal to the cuff, each of which is expected to include full PPG pulse if PPG pulse appears at the corresponding time, are determined through the corresponding segments in the PPG signal in the other hand, taken from time-point of maximum derivative (t_DMXF) to next time-point of maximum derivative, where time-points of the maximum derivative of the PPG signal distal to the cuff are determined in sections with delay relative to the time-points t_DMXF of the maximum derivative points of the PPG pulses in the free hand.

34. A device as in claim 33, wherein the said sections are chosen from t_DMXF+50 ms to t_DMXF+120 ms.

35. A device as in claim 30, wherein the said pulse pattern is determined by subtracting the line connecting the point of the maximum derivative of the pulse to the next maximum derivative point from the output of the PPG sensor distal to the cuff, and calculating the integral of the difference between the said output and the said line for the first half (INT1) and the second half (INT2) of the segment, and the difference between the integral values for the two halves (INT1−

INT2) is taken as pulse pattern parameter.

36. A device as in claim 30, wherein the correlation of the signal in each segment with the signal in the neighboring segment is performed by eliminating sampling points from the longer segment if the two segments are not equal.

37. A device as in claim 30, wherein the average value of PPP for the hand distal to the hand before the inflation (PPP_IN) is calculated, and the first PPG pulse is taken as the first of seven consecutive segments in which at least five segments have correlation coefficient value higher than predetermined specific value, and PPP value higher than predetermined specific fraction of PPP_IN, provided that the said first pulse have correlation coefficient value higher than that said predetermined specific value, and PPP value higher than that said predetermined specific fraction of PPP_IN.

38. A device as in claim 37, wherein the said predetermined specific fraction of the correlation coefficient is in the region of 0.65-0.85, and the said predetermined specific fraction of PPP_IN is in the region of 1-10% of PPP_IN.

39. A device as in claim 29, wherein SBP is replaced by pulse pressure defined by the difference between SBP and diastolic blood pressure.

40. A device as in claim 29, wherein SBP is replaced by diastolic blood pressure.