Pulse wave velocity measuring device

• US 6,331,162 B1
• Filed: 01/28/2000
• Issued: 12/18/2001
• Est. Priority Date: 02/01/1999
• Status: Expired due to Term

• Current Assignee: Gary F. Mitchell
• Original Assignee: Gary F. Mitchell
• Inventors: Mitchell, Gary F.
• Primary Examiner(s): Nasser, Robert L.
• Application Number:
  US09/493,892
• Time in Patent Office: 690 Days
• Field of Search: 600/485, 600/500-503, 600/507
• US Class Current: 600/485
• CPC Class Codes: A61B 5/02125 of pulse wave propagation time
• CPC Class Codes: A61B 5/02416 using photoplethysmograph signals, e.g. generated by infrared radiation A61B5/14552 takes precedence
• CPC Class Codes: A61B 5/0285 Measuring or recording phase velocity of blood waves
• CPC Class Codes: A61B 5/0295 using plethysmography, i.e. measuring the variations in the volume of a body part as modified by the circulation of blood therethrough, e.g. impedance plethysmography
• CPC Class Codes: A61B 5/318 Heart-related electrical modalities, e.g. electrocardiography [ECG]
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives

Abstract

A pulse wave velocity measuring device generally comprises first and second photoplethysmographic transducers or probes electrically operably connected to a computer. The transducers are positioned on a patient'"'"'s back to record pulse waveform information at two locations along the descending thoracic aorta. Additionally, the patient'"'"'s ECG is recorded. Once the pulse waveforms and ECG waveform are recorded, noise or artifact ridden data is excluded, and the pulse waveforms are signal averaged using the ECG data points as fiducial references. Then, the signal averaged pulse waveforms are analyzed (again, with the ECG data providing fiducial points) to determine the foot of each waveform and the foot-to-foot transit time between the two transducers. Pulse wave velocity is then determined by dividing the distance between the transducers by the foot-to-foot transit time. Additionally, a mouthpiece pressure transducer and related circuitry can be connected to the computer for measuring a patient'"'"'s pulse wave velocity as a function of blood pressure.

Claims

1. A method for determining the pulse wave velocity of blood in the descending thoracic aorta comprising the steps of:

a. obtaining a first pulse waveform of blood in blood vessels near a first location on the surface of a patient'"'"'s skin and proximate the fourth thoracic vertebra;

b. obtaining a second pulse waveform of blood in blood vessels near a second location on the surface of the skin and proximate the second lumbar vertebra; and

c. calculating a pulse wave velocity by;

i. determining a first reference point on the first pulse waveform;

ii. using a fiducial reference point to determine a corresponding second reference point on the second pulse waveform;

iii. determining a time difference between the first and second reference points; and

iv. dividing a distance between the first and second surface locations by the time difference.

2. A method for determining the pulse wave velocity of blood in a blood vessel having a substantially uniform and symmetric distribution of branching blood vessels, the method comprising the steps of:

a. obtaining a first pulse waveform of blood in blood vessels proximate a first location on the surface of a patient'"'"'s skin and associated with a first location along the blood vessel;

b. obtaining a second pulse waveform of blood in blood vessels proximate a second location on the surface of the skin and associated with a second location along the blood vessel;

c. calculating a pulse wave velocity by;

i. determining a foot of the first pulse waveform;

ii. determining a foot of the second pulse waveform;

iii. determining a time difference between the foot of the first pulse waveform and the foot of the second pulse waveform; and

iv. dividing a distance between the first and second surface locations by the time difference

d. repeating steps a-c to calculate a plurality of pulse wave velocities;

e. excluding any pulse wave velocities that fall without a predetermined percentage of a mean pulse wave velocity; and

f. averaging the remaining pulse wave velocities.

3. A method for determining pulse wave velocity in a blood vessel having a substantially uniform and symmetric distribution of branching blood vessels, the method comprising the steps of:

a. obtaining a first pulse waveform of blood in blood vessels proximate a first location on the surface of a patient'"'"'s skin and associated with a first location along the blood vessel;

b. obtaining a second pulse waveform of blood in blood vessels proximate a second location on the surface of the skin and associated with a second location along the blood vessel;

c. separately signal averaging the first and second pulse waveforms, wherein one of the pulse waveforms is used to provide at least one fiducial point for signal averaging the pulse waveforms; and

d. calculating a pulse wave velocity by;

i. determining a foot of the first pulse waveform;

ii. determining a foot of the second pulse waveform;

iii. determining a time difference between the foot of the first pulse waveform and the foot of the second pulse waveform; and

iv. dividing a distance between the first and second surface locations by the time difference.

4. A method for determining pulse wave velocity in a blood vessel having a substantially uniform and symmetric distribution of branching blood vessels, the method comprising the steps of:

a. obtaining a first pulse waveform of blood in blood vessels proximate a first location on the surface of a patient'"'"'s skin and associated with a first location along the blood vessel;

b. obtaining a second pulse waveform of blood in blood vessels proximate a second location on the surface of the skin and associated with a second location along the blood vessel; and

c. calculating a pulse wave velocity by;

i. determining a foot of the first pulse waveform;

ii. determining a foot of the second pulse waveform;

iii. determining a time difference between the foot of the first pulse waveform and the foot of the second pulse waveform; and

iv. dividing a distance between the first and second surface locations by the time difference;

d. wherein the step of determining each foot of the pulse waveforms comprises the sub-steps of;

i. calculating a derivative of the pulse wave signal;

ii. determining a peak of the derivative;

iii. determining a first threshold value of the derivative;

iv. determining a second threshold value of the derivative less than the first threshold value;

v. searching forward in time from a fiducial point to determine a first point on the derivative that is the first to exceed the first threshold; and

vi. searching back in time along the derivative to determine a second point on the derivative that is the first to exceed the second threshold, wherein the second point on the derivative is the foot of the pulse waveform.

5. The method of claim 4 further comprising the steps of:

obtaining an ECG waveform; and

determining a peak of a QRS portion of the ECG waveform for use as the fiducial point.

6. The method of claim 4 wherein the fiducial point is the peak of the derivative.

7. The method of claim 4 wherein:

a. the first threshold value is equal to 50% of the peak of the derivative; and

b. the second threshold value is equal to 20% of the peak of the derivative.

8. A device for measuring pulse wave velocity in a blood vessel having a substantially uniform and symmetric distribution of branching blood vessels, the device comprising:

a. a signal analyzing means for analyzing signals; and

b. first and second transducers operably electrically connected to the signal analyzing means, wherein the transducers are configured to respectively provide to the signal analyzing means first and second pulse wave signals corresponding to pulse waveforms in blood vessels proximate first and second locations on the surface of a patient'"'"'s skin and associated with first and second locations along the blood vessel;

c. wherein the signal analyzing means is configured;

i. to record the pulse wave signals;

ii. to display the recorded pulse wave signals and to allow a user to designate portions of the recorded pulse wave signals that are not to be used in signal averaging the pulse wave signals;

iii. to signal average the pulse wave signals;

iv. to use a fiducial reference point to determine a first reference point on the first pulse wave signal and a corresponding second reference point on the second pulse waveform;

v. to determine a time difference between the first and second reference points; and

vi. to calculate the pulse wave velocity by dividing a distance between the first and second surface locations by the time difference.

9. A device for measuring pulse wave velocity in a blood vessel having a substantially uniform and symmetric distribution of branching blood vessels, the device comprising:

a. a signal analyzing means for analyzing signals; and

b. first and second transducers operably electrically connected to the signal analyzing means, wherein the transducers are configured to respectively provide to the signal analyzing means first and second pulse wave signals corresponding to pulse waveforms in blood vessels proximate first and second locations on the surface of a patient'"'"'s skin and associated with first and second locations along the blood vessel;

c. wherein the signal analyzing means is configured;

i. to use a fiducial reference point to determine a foot of the first pulse wave signal and a corresponding foot of the second pulse waveform, wherein for determining the foot of each pulse wave signal, the signal analyzing means is configured;

A. to calculate a derivative of the pulse wave signal;

B. to determine a peak of the derivative;

C. to determine a first threshold value for the derivative equal to 50% of its peak;

D. to determine a second threshold value for the derivative equal to 20% of its peak;

E. to determine a first point on the derivative forward in time from a fiducial point that is the first to exceed the first threshold; and

,

F. searching back in time along the derivative, to determine a second point on the derivative that is the first to exceed the second threshold, wherein the second point on the derivative is the foot of the pulse wave signal;

ii. to determine a time difference between the first and second reference points; and

iii. to calculate the pulse wave velocity by dividing a distance between the first and second surface locations by the time difference.

11. The device of claim 9 wherein the signal analyzing means is configured to use the peak of the QRS as the second fiducial point in determining the reference point on each pulse wave signal.

10. A device for measuring pulse wave velocity in a blood vessel having a substantially uniform and symmetric distribution of branching blood vessels, the device comprising:

a. a signal analyzing means for analyzing signals;

b. first and second transducers operably electrically connected to the signal analyzing means, wherein the transducers are configured to respectively provide to the signal analyzing means first and second pulse wave signals corresponding to pulse waveforms in blood vessels proximate first and second locations on the surface of a patient'"'"'s skin and associated with first and second locations along the blood vessel; and

c. an ECG recording device operably electrically connected to the signal analyzing means and configured to provide to the signal analyzing means an ECG signal corresponding to a patient'"'"'s ECG;

d. wherein the signal analyzing means is configured;

i. to determine a peak of a QRS of the ECG signal;

ii. to record and signal average the pulse wave signals, using the QRS peak as a first fiducial point,

iii. to use a second fiducial reference point to determine a first reference point on the first pulse wave signal and a corresponding second reference point on the second pulse waveform;

iv. to determine a time difference between the first and second reference points; and

v. to calculate the pulse wave velocity by dividing a distance between the first and second surface locations by the time difference.

12. A method for determining pulse wave velocity in a blood vessel having a substantially uniform and symmetric distribution of branching blood vessels, the method comprising the steps of:

a. obtaining a first pulse waveform of blood in blood vessels proximate a first location on the surface of a patient'"'"'s skin and associated with a first location along the blood vessel;

b. obtaining a second pulse waveform of blood in blood vessels proximate a second location on the surface of the skin and associated with a second location along the blood vessel;

c. calculating a pulse wave velocity by;

i. determining a first reference point on the first pulse waveform;

ii. determining a corresponding second reference point on the second pulse waveform;

iii. determining a time difference between the first and second reference points; and

iv. dividing a distance between the first and second surface locations by the time difference;

d. repeating steps a-c to calculate a plurality of pulse wave velocities;

e. excluding any pulse wave velocities that fall without a predetermined percentage of a mean pulse wave velocity; and

f. averaging the remaining pulse wave velocities.

13. A method for determining pulse wave velocity in a blood vessel having a substantially uniform and symmetric distribution of branching blood vessels, the method comprising the steps of:

a. obtaining a first pulse waveform of blood in blood vessels proximate a first location on the surface of a patient'"'"'s skin and associated with a first location along the blood vessel;

b. obtaining a second pulse waveform of blood in blood vessels proximate a second location on the surface of the skin and associated with a second location along the blood vessel; and

c. calculating a pulse wave velocity by;

i. determining a first reference point on the first pulse waveform;

ii. determining a corresponding second reference point on the second pulse waveform;

iii. determining a time difference between the first and second reference points; and

iv. dividing a distance between the first and second surface locations by the time difference;

d. wherein the steps of determining the first and second reference points on the pulse waveforms each comprise the sub-steps of;

i. calculating a derivative of the pulse wave signal;

ii. determining a peak of the derivative;

iii. determining a threshold value of the peak of the derivative; and

iv. searching along the derivative to determine a point on the derivative at the threshold value, wherein that point is the reference point on the pulse waveform.

14. A method for determining pulse wave velocity in a blood vessel comprising the steps of:

a. obtaining a pulse waveform of blood in blood vessels proximate each of a plurality of spaced-apart locations on the surface of the skin and associated with a plurality of spaced-apart locations along the blood vessel;

b. using a fiducial reference point, determining corresponding reference points on the pulse waveforms; and

c. applying linear regression analysis to the corresponding reference points on the pulse waveforms to determine pulse wave velocity.

15. The method of claim 14 wherein the reference point on each pulse waveform is the foot of the pulse waveform, as determined in each case by:

a. calculating a derivative of the pulse waveform;

b. determining a peak of the derivative;

c. determining at least one threshold value of the peak of the derivative; and

d. searching along the derivative to determine a point on the derivative at the threshold value, wherein that point is foot of the pulse wave signal.

16. The method of claim 14 wherein the reference point on each pulse waveform is the foot of the pulse waveform, as determined in each case by:

a. calculating a derivative of the pulse waveform;

b. determining a peak of the derivative;

c. determining a first threshold value of the derivative;

d. determining a second threshold value of the derivative less than the first threshold value;

e. searching forward in time from a fiducial point to determine a first point on the derivative that is the first to exceed the first threshold; and

f. searching back in time along the derivative to determine a second point on the derivative that is the first to exceed the second threshold, wherein the second point on the derivative is the foot of the pulse waveform.

17. The method of claim 14 wherein the method further comprises the step of separately signal averaging the pulse waveforms, wherein one of the pulse waveforms is used to provide at least one fiducial point for signal averaging the pulse waveforms.

18. The method of claim 17 wherein the pulse waveforms are screened for extraneous noise content and waveform shape, and the highest quality pulse waveform is used to provide the at least one fiducial point for signal averaging the pulse waveforms.

19. The method of claim 14 wherein the step of applying linear regression analysis is performed with respect to a fiducial point provided by one of the pulse waveforms.

20. The method of claim 14 wherein the step of applying linear regression analysis is performed with respect to a fiducial point provided by a recorded ECG waveform.

21. A method for determining pulse wave velocity in a blood vessel comprising the steps of:

a. obtaining a pulse waveform of blood in blood vessels proximate each of at least three spaced-apart locations on the surface of the skin and associated with at least three spaced-apart locations along the blood vessel;

b. using a fiducial reference point, determining corresponding reference points on the pulse waveforms and the relative time delays from the fiducial reference point to the corresponding reference points; and

c. using linear regression analysis to calculate pulse wave velocity, wherein the slope of a generally linear relationship between the corresponding reference points, each as a function of respective location on the surface of the skin versus relative time delay, is the pulse wave velocity.

22. The method of claim 21 further comprising the steps of:

a. determining if any of the corresponding reference points, as a function of respective location on the surface of the skin versus relative time delay, fall substantially outside the linear relationship; and

b. recalculating pulse wave velocity without the corresponding reference points that fall substantially outside the linear relationship.

23. A method for determining pulse wave velocity in a blood vessel comprising the steps of:

a. obtaining a pulse waveform of blood in blood vessels proximate each of a plurality of spaced-apart locations on the surface of the skin and associated with a plurality of spaced-apart locations along the blood vessel;

b. separately signal averaging the pulse waveforms, wherein one of the pulse waveforms is used to provide at least one first fiducial point for signal averaging the pulse waveforms; and

c. calculating a pulse wave velocity by;

i. determining corresponding reference points on the pulse waveforms, wherein each corresponding reference point has an associated time point; and

ii. determining a generally linear relationship between the time points and the spaced-apart locations on the surface of the skin, wherein the generally linear relationship is the pulse wave velocity.

24. The method of claim 23 wherein the step of determining the generally linear relationship comprises the sub-steps of determining the time differences between the corresponding reference points;

and dividing the distances between the spaced-apart locations on the surface of the skin by respective time differences.

25. The method of claim 23 wherein the step of determining the generally linear relationship comprises using linear regression analysis to calculate pulse wave velocity, wherein the slope of the generally linear relationship between the corresponding reference points, each as a function of respective location on the surface of the skin versus relative time delay, is the pulse wave velocity.

26. The method of claim 23 wherein the pulse waveforms are screened for extraneous noise content and waveform shape, and the highest quality pulse waveform is used to provide the at least one first fiducial point for signal averaging the pulse waveforms.

27. The method of claim 23 wherein one of the pulse waveforms is also used to provide at least one second fiducial point for determining the corresponding reference points on the pulse waveforms.

28. A method for determining pulse wave velocity in a blood vessel comprising the steps of:

a. obtaining pulse waveforms at least three spaced-apart locations along the blood vessel;

b. using a fiducial reference point, determining corresponding reference points on the pulse waveforms; and

c. applying linear regression analysis to the corresponding reference points on the pulse waveforms to determine pulse wave velocity.

29. The method of claim 28 further comprising the step of separately signal averaging the pulse waveforms using at least one fiducial provided by one of the pulse waveforms.

30. A device for measuring pulse wave velocity in a blood vessel comprising:

a. a signal analyzer; and

b. at least three transducers operably electrically connected to the signal analyzer, wherein the transducers are configured to provide to the signal analyzer respective pulse wave signals corresponding to pulse waveforms in blood vessels proximate a plurality of spaced-apart locations on the surface of the skin and associated with at least three spaced-apart locations along the blood vessel;

c. wherein the signal analyzer is configured;

i. to record the pulse wave signals;

ii. using a fiducial reference point, to determine corresponding reference points on the pulse wave signals and the relative time delays from the fiducial reference point to the corresponding reference points; and

iii. to calculate pulse wave velocity using linear regression analysis, wherein the slope of a generally linear relationship between the corresponding reference points, each as a function of respective location on the surface of the skin versus relative time delay, is the pulse wave velocity.

31. A device for measuring pulse wave velocity in a blood vessel comprising:

a. a signal analyzer; and

b. a plurality of transducers operably electrically connected to the signal analyzer, wherein the transducers are configured to provide to the signal analyzer respective pulse wave signals corresponding to pulse waveforms in blood vessels proximate a plurality of spaced-apart locations on the surface of the skin and associated with a plurality of spaced-apart locations along the blood vessel;

c. wherein the signal analyzer is configured;

i. to record the pulse wave signals;

ii. to separately signal average the pulse wave signals, with one of the pulse wave signals being used to provide at least one first fiducial point for signal averaging the pulse wave signals; and

iii. to calculate a pulse wave velocity by;

determining corresponding reference points on the pulse wave signals, wherein each corresponding reference point has an associated time point; and

determining a generally linear relationship between the time points and the spaced-apart locations on the surface of the skin, wherein the generally linear relationship is the pulse wave velocity.