Apparatus and method for blood pressure pulse waveform contour analysis

• US 6,394,958 B1
• Filed: 11/05/1999
• Issued: 05/28/2002
• Est. Priority Date: 03/20/1998
• Status: Expired due to Term

• Current Assignee: Hypertension Diagnostics, Inc.
• Original Assignee: Hypertension Diagnostics, Inc.
• Inventors: Bratteli, Christopher W., Morgan, Dennis J., Cohn, Jay N., Finkelstein, Stanley M.
• Primary Examiner(s): Lacyk, John P.
• Assistant Examiner(s): ASTORINO, MICHAEL C
• Application Number:
  US09/434,077
• Time in Patent Office: 935 Days
• Field of Search: 600/300,301,481-486,500-508,513-515
• 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 5/02108 from analysis of pulse wave characteristics
• CPC Class Codes: A61B 5/7239 using differentiation including higher order derivatives
• CPC Class Codes: A61B 7/00 Instruments for auscultation
• CPC Class Codes: A61B 7/045 Detection of Korotkoff sounds A61B5/0225 takes precedence; measuring blood pressure A61B5/021

Abstract

Methods and apparatus for processing an arterial blood pressure waveform to extract clinically useful information on the state of the cardiovascular system are disclosed herein. In order to obtain the parameters of the modified Windkessel model, the diastolic portion of a subject'"'"'s blood pressure waveform is scanned over a plurality of ranges and the range that produces the best fit of data and lowest error estimates are selected. In addition, multiple empirically determined starting values of the ‘A’ parameters are used to find the best fit of the model data to the actual arterial blood pressure waveform data.

Claims

1. Apparatus for analyzing a digitized arterial blood pressure waveform comprising a computer programmed to carry out the steps of:

a) identifying a diastolic portion of the waveform starting at an initial point;

b) fitting a mathematical model of a curve to the diastolic portion of the waveform to determine a first set of curve fitting parameters;

c) fitting the mathematical model to the diastolic portion of the waveform to determine a second set of curve fitting parameters;

d) determining a first model parameter of an electrical analog model of a vasculature for each of the first and second sets of curve fitting parameters;

e) determining an estimate of the error associated with each of the first model parameters; and

f) selecting as superior the first model parameter with the least error associated with it.

8. The apparatus of claim 1, wherein the first model parameter is selected from the group:

C₁=proximal or capacitive compliance,

C₂=distal or reflective or oscillatory compliance, and

L=inertance.

9. The apparatus of claim 1, wherein the computer is further programmed to perform the step:

g) identifying a near-notch region of the waveform around a dicrotic notch of the waveform, wherein the first set of curve fitting parameters are determined by defining the diastolic portion of the waveform to begin at a first point within the near-notch region, and the second set of curve fitting parameters are determined by defining the diastolic portion of the waveform to begin at a second point within the near-notch region, where the first and second points are different.

2. Apparatus for analyzing a digitized arterial blood pressure waveform comprising

a computer programmed to carry out the steps of:

a) identifying a diastolic portion of the waveform starting at an initial point;

b) fitting a mathematical model of a curve to the identified diastolic portion of the waveform to determine a first set of curve fitting parameters using a first set of initial condition parameters as an initial condition;

c) fitting the mathematical model to the diastolic portion of the waveform to determine one or more additional sets of curve fitting parameters using one or more additional sets of initial condition parameters as initial conditions wherein each set of initial conditions are different from one another;

d) determining a measure of the quality of fit for each set of curve fitting parameters to identify sets of parameters that meet a minimum requirement;

e) determining one or more model parameters of an electrical analog model of the vasculature using each of the sets of the curve fitting parameters that meet the minimum requirement; and

f) changing the identified diastolic portion of the waveform and repeating steps b, c, d and e.

10. The apparatus of claim 2, wherein the one or more model parameters are selected from the group:

C₁=proximal or capacitive compliance,

C₂=distal or reflective or oscillatory compliance, and

L=inertance.

11. The apparatus of claim 2, wherein the step f) of changing the identified diastolic portion of the waveform comprises:

f)(1) identifying a near-notch region of the waveform around a dicrotic notch of the waveform; and

f)(2) marking a point on the waveform within the near-notch region as the onset of diastole, wherein the point is different than the initial point.

3. Apparatus for identifying a diastolic portion including an onset of diastole and an end of diastole of a digitized arterial blood pressure waveform, the waveform including a dicrotic notch, comprising a computer programmed to carry out the steps of:

a) identifying a near-notch region of the waveform around the dicrotic notch;

b) marking a point on the waveform within the near-notch region as the onset of diastole; and

c) marking a point representative of the end of diastole.

12. The apparatus of claim 3, wherein the step a) of identifying the near-notch region comprises bracketing the dicrotic notch based on derivatives of the waveform.

13. The apparatus of claim 3, wherein the step a) of identifying the near-notch region comprises:

a)(1) low-pass filtering the waveform between systole and end diastole for each beat to obtain a filtered waveform; and

a)(2) bracketing the dicrotic notch based on derivatives of the filtered waveform.

14. The apparatus of claim 3, wherein the step a) of identifying the near-notch region comprises:

a)(1) low-pass filtering the waveform between systole and end diastole for each beat using an eight-pole low-pass Butterworth filter with an attenuation of about 6 dB at its corner frequency to obtain a filtered waveform; and

a)(2) bracketing the dicrotic notch based on derivatives of the filtered waveform.

15. The apparatus of claim 3, wherein the computer is further programmed to perform the steps:

d) fitting a mathematical model of a curve to a first diastolic portion of the waveform starting at a first point within the region to determine a first set of curve fitting parameters;

e) fitting the mathematical model to a second diastolic portion of the waveform starting at a second point different than the first point within the region to determine a second set of curve fitting parameters;

f) determining a first model parameter of an electrical analog model of a vasculature for each of the first and second sets of curve fitting parameters;

g) determining an estimate of the error associated with each of the first model parameters; and

h) selecting as superior the first model parameter with the least error associated with it.

17. The method of claim 12, further comprising the step:

g) identifying a near-notch region of the waveform around a dicrotic notch of the waveform, wherein the first set of curve fitting parameters are determined by defining the diastolic portion of the waveform to begin at a first point within the near-notch region, and the second set of curve fitting parameters are determined by defining the diastolic portion of the waveform to begin at a second point within the near-notch region, where the first and second points are different.

4. A method for analyzing a digitized arterial blood pressure waveform using a computer comprising the steps of:

a) identifying a diastolic portion of the waveform starting at an initial point;

b) fitting a mathematical model of a curve to the diastolic portion of the waveform to determine a first set of curve fitting parameters;

c) fitting the mathematical model to the diastolic portion of the waveform to determine a second set of curve fitting parameters;

d) determining a first model parameter of an electrical analog model of a vasculature for each of the first and second sets of curve fitting parameters;

e) determining an estimate of the error associated with each of the first model parameters; and

f) selecting as superior the first model parameter with the least error associated with it.

16. The method of claim 4, wherein the first model parameter is selected from the group:

C₁=proximal or capacitive compliance,

C₂=distal or reflective or oscillatory compliance, and

L=inertance.

5. A method for analyzing a digitized arterial blood pressure waveform using a computer comprising the steps of:

a) identifying a diastolic portion of the waveform;

b) fitting a mathematical model of a curve to the identified diastolic portion of the waveform to determine a first set of curve fitting parameters using a first set of initial condition parameters as an initial condition;

c) fitting the mathematical model to the diastolic portion of the waveform to determine one or more additional sets of curve fitting parameters using one or more additional sets of initial condition parameters as initial conditions wherein each set of initial conditions are different from one another;

d) determining a measure of the quality of fit for each set of curve fitting parameters to identify sets of parameters that meet a minimum requirement;

e) determining one or more model parameters of an electrical analog model of the vasculature using each of the sets of the curve fitting parameters that meet the minimum requirement; and

f) changing the identified diastolic portion of the waveform and repeating steps b, c, d and e.

18. The method of claim 5, wherein the one or more model parameters are selected from the group:

C₁=proximal or capacitive compliance,

C₂=distal or reflective or oscillatory compliance, and

L=inertance.

19. The method of claim 5, wherein the step f) of changing the identified diastolic portion of the waveform comprises:

f)(1) identifying a near-notch region of the waveform around a dicrotic notch of the waveform; and

f)(2) marking a point on the waveform within the near-notch region as the onset of diastole, wherein the point is different than the initial point.

6. A method for identifying a diastolic portion of a digitized arterial blood pressure waveform comprising:

a) identifying a region of the waveform around the dicrotic notch;

b) marking a point on the waveform within the region as the onset of diastole;

c) marking a point representative of the end of diastole; and

d) marking the point representative of the end of diastole based on the decay of the waveform being monotonic.

7. A method for computer analysis of a digitized blood pressure waveform using an electrical analog model of the vasculature comprising identifying a superior model parameter from more than one model parameter wherein each model parameter is fit to the model, wherein the superior model parameter is determined by reference to an estimate of the error associated with each parameter.

24. The method of claim 7, wherein each one of the more than one model parameters are selected from the group:

C₁=proximal or capacitive compliance,

C₂=distal or reflective or oscillatory compliance, and

L=inertance.

20. A method for identifying a diastolic portion of a digitized arterial blood pressure waveform comprising the steps of:

a) identifying a region of the waveform around the dicrotic notch;

b) marking a point on the waveform within the region as the onset of diastole; and

c) marking a point representative of the end of diastole,

wherein the a) identifying the near-notch region comprises bracketing the dicrotic notch based on derivatives of the waveform.

30. The method of claim 20, further comprising:

d) fitting a mathematical model of a curve to the diastolic portion of the waveform to determine a first set of curve fitting parameters;

e) fitting the mathematical model to the diastolic portion of the waveform to determine a second set of curve fitting parameters;

f) determining a first model parameter of an electrical analog model of a vasculature for each of the first and second sets of curve fitting parameters;

g) determining an estimate of the error associated with each of the first model parameters; and

h) selecting as superior the first model parameter with the least error associated with it.

21. A method for identifying a diastolic portion of a digitized arterial blood pressure waveform comprising:

a) identifying a region of the waveform around the dicrotic notch;

b) marking a point on the waveform within the region as the onset of diastole; and

c) marking a point representative of the end of diastole,

wherein the a) identifying the near-notch region comprises bracketing the dicrotic notch from a positive-going zero-crossing of a second derivative of the waveform to a following negative-going zero-crossing of the second derivative of the waveform.

22. A method for identifying a diastolic portion of a digitized arterial blood pressure waveform comprising:

a) identifying a region of the waveform around the dicrotic notch;

b) marking a point on the waveform within the region as the onset of diastole; and

c) marking a point representative of the end of diastole,

wherein the a) identifying the near-notch region comprises;

a)(1) low-pass filtering the waveform between systole and end diastole for each beat to obtain a filtered waveform; and

a)(2) bracketing the dicrotic notch based on derivatives of the filtered waveform.

23. A method for identifying a diastolic portion of a digitized arterial blood pressure waveform comprising:

a) identifying a region of the waveform around the dicrotic notch;

b) marking a point on the waveform within the region as the onset of diastole; and

c) marking a point representative of the end of diastole,

wherein the a) identifying the near-notch region comprises;

a)(1) low-pass filtering the waveform between systole and end diastole for each beat using an eight-pole low-pass Butterworth filter with an attenuation of about 6 dB at its corner frequency to obtain a filtered waveform; and

a)(2) bracketing the dicrotic notch from a positive-going zero-crossing of a second derivative of the waveform to a following negative-going zero-crossing of the second derivative of the filtered waveform.

25. A method for identifying a diastolic portion of a digitized arterial blood pressure waveform comprising the steps of:

a) identifying a region of the waveform around the dicrotic notch;

b) marking a point on the waveform within the region as the onset of diastole;

c) marking a point representative of the end of diastole;

d) fitting a mathematical model of a curve to a first diastolic portion of the waveform starting at a first point within the region to determine a first set of curve fitting parameters;

e) fitting the mathematical model to a second diastolic portion of the waveform starting at a second point different than the first point within the region to determine a second set of curve fitting parameters;

f) determining a first model parameter of an electrical analog model of a vasculature for each of the first and second sets of curve fitting parameters;

g) determining an estimate of the error associated with each of the first model parameters; and

h) selecting as superior the first model parameter with the least error associated with it.

26. A method for computer analysis of a digitized blood pressure waveform using an electrical analog model of the vasculature comprising identifying a superior value of a first model parameter from more than one value of the first model parameter wherein each value of the first model parameter is determined from parameters fit to the model, wherein the superior value of the first model parameter is determined by reference to an estimate of the error associated with each value.

27. The method of claim 26, wherein each one of the more than one value for the first model parameter is based on a different starting point of a diastolic portion of the waveform.

28. The method of claim 26, wherein each one of the more than one value for the first model parameter is based on a different starting point of a diastolic portion of one beat of the form.

29. The method of claim 26, wherein the first model parameter is selected from the group:

C₁=proximal or capacitive compliance,

C₂=distal or reflective or oscillatory compliance, and

L=inertance.