Calibrating for Blood Pressure Using Height Difference

• US 20160302677A1
• Filed: 04/12/2016
• Published: 10/20/2016
• Est. Priority Date: 04/14/2015
• Status: Active Application

• Current Assignee: Robert F. Dudley
• Original Assignee: Quanttus Inc
• Inventors: He, David Da
• Application Number:
  US15/096,627
• Publication Number:
  US 20160302677A1
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: A61B 2503/12 Healthy persons not otherwise provided for, e.g. subjects of a marketing survey
• CPC Class Codes: A61B 2503/22 Motor vehicles operators, e.g. drivers, pilots, captains
• CPC Class Codes: A61B 2505/01 Emergency care
• CPC Class Codes: A61B 2560/0223 of calibration, e.g. protocols for calibrating sensors
• CPC Class Codes: A61B 5/0205 Simultaneously evaluating both cardiovascular conditions and different types of body conditions, e.g. heart and respiratory condition
• CPC Class Codes: A61B 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/02405 Determining heart rate variability
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/1102 Ballistocardiography
• CPC Class Codes: A61B 5/117 Identification of persons methods or arrangements for recognising patterns, e.g. fingerprints, G06F18/00, G06V40/00; identification of persons by analysing their voice or speech G10L17/00
• CPC Class Codes: A61B 5/681 Wristwatch-type devices
• CPC Class Codes: A61B 5/7275 Determining trends in physiological measurement data; Predicting development of a medical condition based on physiological measurements, e.g. determining a risk factor
• CPC Class Codes: A61B 5/743 Displaying an image simultaneously with additional graphical information, e.g. symbols, charts, function plots

Abstract

The technology described in this document can be embodied in a method that includes obtaining a first pulse transit time (PTT) measurement and a second PTT measurement for a subject. The PTT represents a time taken by a pulse pressure wave traveling to the wrist of the subject. The first PTT is measured when the wrist of the subject is at a first height, and the second PTT is measured when the wrist of the subject is at a second height. The method also includes computing a hydrostatic difference in blood pressure as a function of the difference between the first height and the second height, and computing a calibration metric as a function of (i) the hydrostatic difference in blood pressure, and (ii) the difference between the first PTT and the second PTT.

Claims

1. A method comprising:

obtaining a first pulse transit time (PTT) measurement for a subject, wherein the PTT represents a time taken by a pulse pressure wave traveling to the wrist of the subject, and wherein the first PTT is measured when the wrist of the subject is at a first height;

obtaining a second PTT measurement for the subject, wherein the second PTT is measured when the wrist of the subject is at a second height;

computing a hydrostatic difference in blood pressure as a function of the difference between the first height and the second height; and

computing a calibration metric as a function of (i) the hydrostatic difference in blood pressure, and (ii) the difference between the first PTT and the second PTT.

2. The method of claim 1, wherein the first PTT is obtained when the subject is in a horizontal position such that the first height is substantially equal to the vertical height of the heart of the subject.

3. The method of claim 1, wherein the second PTT is obtained when the subject is in a vertical position.

4. The method of claim 3, wherein the difference between the first height and the second height is estimated based on information on the height of the subject.

5. The method of claim 4, wherein estimating the difference between the first height and the second height comprises estimating a height difference between the wrist and the heart of the subject when the subject is in the vertical position with the corresponding arm of the subject in a substantially straight vertical configuration.

6. The method of claim 1, further comprising using the calibration metric to adjust a blood pressure value to compensate for hydrostatic differences.

7. The method of claim 1, wherein the hydrostatic difference in blood pressure is determined as a function of a product of (i) the difference between the first height and the second height, (ii) density of blood of the subject, and (iii) acceleration due to gravity.

8. The method of claim 1, wherein measuring the first PTT or the second PTT comprises:

obtaining, using a first sensor disposed in a device, a first data set representing time-varying information on at least one pulse pressure wave within vasculature at the wrist of the subject;

obtaining, using a second sensor disposed in the device, a second data set representing time-varying information about motion data of the subject;

identifying, using one or more processors, a first point in the first data set, the first point representing an arrival time of the pulse pressure wave at the wrist;

identifying, using the one or more processors, a second point in the second dataset, the second point representing an earlier time at which the pulse pressure wave originates at the heart of the subject; and

computing the first PTT or the second PTT as a difference between the first and second points.

9. The method of claim 8, wherein the information about the at least one pulse pressure wave comprises photoplethysmographic (PPG) data and the information about the motion of the subject comprises motion cardiogram (MoCG) or seismocardiogram (SCG) data.

10. The method of claim 8, wherein the device is worn by the subject on the wrist.

11. The method of claim 8, wherein the first sensor comprises an optical sensor and the second sensor comprises an accelerometer.

12. The method of claim 8, further comprising computing a blood pressure of the subject as a parameterized function of the first PTT or the second PTT.

13. The method of claim 12, further comprising calibrating one or more parameters of the parameterized function based on a measured blood pressure.

14. The method of claim 1, wherein the first PTT is obtained automatically when the subject is lying in a horizontal position, and the second PTT is obtained automatically when the subject is in a vertical position.

15. One or more machine-readable storage devices storing instructions that are executable by one or more processing devices to perform operations comprising:

obtaining a first pulse transit time (PTT) measurement for a subject, wherein the PTT represents a time taken by a pulse pressure wave traveling to the wrist of the subject, and wherein the first PTT is measured when the wrist of the subject is at a first height;

obtaining a second PTT measurement for the subject, wherein the second PTT is measured when the wrist of the subject is at a second height;

computing a hydrostatic difference in blood pressure as a function of the difference between the first height and the second height; and

computing a calibration metric as a function of (i) the hydrostatic difference in blood pressure, and (ii) the difference between the first PTT and the second PTT.

16. The one or more machine-readable storage devices of claim 15, wherein the first PTT is obtained when the subject is in a horizontal position such that the first height is substantially equal to the vertical height of the heart of the subject.

17. The one or more machine-readable storage devices of claim 15, wherein the second PTT is obtained when the subject is in a vertical position.

18. The one or more machine-readable storage devices of claim 17, wherein the difference between the first height and the second height is estimated based on information on the height of the subject.

19. The one or more machine-readable storage devices of claim 18, wherein estimating the difference between the first height and the second height comprises estimating a height difference between the wrist and the heart of the subject when the subject is in the vertical position with the corresponding arm of the subject in a substantially straight vertical configuration.

20. The one or more machine-readable storage devices of claim 15, further comprising using the calibration metric to adjust a blood pressure value to compensate for hydrostatic differences.

21. The one or more machine-readable storage devices of claim 15, wherein the hydrostatic difference in blood pressure is determined as a function of a product of (i) the difference between the first height and the second height, (ii) density of blood of the subject, and (iii) acceleration due to gravity.

22. The one or more machine-readable storage devices of claim 15, wherein measuring the first PTT or the second PTT comprises:

obtaining, using a first sensor disposed in a device, a first data set representing time-varying information on at least one pulse pressure wave within vasculature at the wrist of the subject;

obtaining, using a second sensor disposed in the device, a second data set representing time-varying information about motion data of the subject;

identifying, using one or more processors, a first point in the first data set, the first point representing an arrival time of the pulse pressure wave at the wrist;

identifying, using the one or more processors, a second point in the second dataset, the second point representing an earlier time at which the pulse pressure wave originates at the heart of the subject; and

computing the first PTT or the second PTT as a difference between the first and second points.

23. The one or more machine-readable storage devices of claim 22, wherein the information about the at least one pulse pressure wave comprises photoplethysmographic (PPG) data and the information about the motion of the subject comprises motion cardiogram (MoCG) or seismocardiogram (SCG) data.

24. The one or more machine-readable storage devices of claim 22, wherein the device is worn by the subject on the wrist.

25. The one or more machine-readable storage devices of claim 22, wherein the first sensor comprises an optical sensor and the second sensor comprises an accelerometer.

26. The one or more machine-readable storage devices of claim 22, further comprising instructions for computing a blood pressure of the subject as a parameterized function of the first PTT or the second PTT.

27. The one or more machine-readable storage devices of claim 26, further comprising instructions for calibrating one or more parameters of the parameterized function based on a measured blood pressure.

28. The one or more machine-readable storage devices of claim 15, wherein the first PTT is obtained automatically when the subject is lying in a horizontal position, and the second PTT is obtained automatically when the subject is in a vertical position.

29. A system comprising:

memory; and

one or more processing devices configured to perform operations comprising;

obtaining a first pulse transit time (PTT) measurement for a subject, wherein the PTT represents a time taken by a pulse pressure wave traveling to the wrist of the subject, and wherein the first PTT is measured when the wrist of the subject is at a first height;

obtaining a second PTT measurement for the subject, wherein the second PTT is measured when the wrist of the subject is at a second height;

computing a hydrostatic difference in blood pressure as a function of the difference between the first height and the second height; and

computing a calibration metric as a function of (i) the hydrostatic difference in blood pressure, and (ii) the difference between the first PTT and the second PTT.

30. The system of claim 29, wherein the first PTT is obtained when the subject is in a horizontal position such that the first height is substantially equal to the vertical height of the heart of the subject.

31. The system of claim 29, wherein the second PTT is obtained when the subject is in a vertical position.

32. The system of claim 31, wherein the difference between the first height and the second height is estimated based on information on the height of the subject.

33. The system of claim 29, wherein the one or more processing devices are configured to use the calibration metric to adjust a blood pressure value to compensate for hydrostatic differences.

34. The system of claim 29, further comprising a first sensor and a second sensor disposed in a device, wherein the one or more processing devices are configured to measure the first PTT or the second PTT by:

obtaining, from the first sensor, a first data set representing time-varying information about at least one pulse pressure wave within vasculature at the wrist of the subject;

obtaining, from the second sensor, a second data set representing time-varying information about motion data of the subject;

identifying a first point in the first data set, the first point representing an arrival time of the pulse pressure wave at the wrist;

identifying a second point in the second dataset, the second point representing an earlier time at which the pulse pressure wave originates at the heart of the subject; and

computing the first PTT or the second PTT as a difference between the first and second points.

35. The system of claim 34, wherein the information about the at least one pulse pressure wave comprises photoplethysmographic (PPG) data and the information about the motion of the subject comprises motion cardiogram (MoCG) or seismocardiogram (SCG) data.

36. The system of claim 34, wherein the device is a wrist-wearable device.

37. The system of claim 34, wherein the first sensor comprises an optical sensor and the second sensor comprises an accelerometer.

38. The system of claim 34, wherein the one or more processing devices are further configured to compute a blood pressure of the subject as a parameterized function of the first PTT or the second PTT.

39. The system of claim 38, wherein the one or more processing devices are configured to calibrate one or more parameters of the parameterized function based on a measured blood pressure.

40. The system of claim 29, wherein the first PTT is obtained automatically when the subject is lying in a horizontal position, and the second PTT is obtained automatically when the subject is in a vertical position.