Apparatus and method for blood pressure pulse waveform contour analysis

• US 6,017,313 A
• Filed: 03/20/1998
• Issued: 01/25/2000
• 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): O'Connor, Cary
• Assistant Examiner(s): ASTORINO, MICHAEL C
• Application Number:
  US09/045,420
• Time in Patent Office: 676 Days
• Field of Search: 600/481, 600/484, 600/485, 600/486, 600/500
• 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) fitting a mathematical model of a curve to a diastolic portion of the waveform to determine a first set of curve fitting parameters;

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

c) 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;

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

e) selecting as superior the first model parameter with the least error associated with it;

f) determining a second model parameter of an electrical analog model of the 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 second model parameters;

h) selecting as superior the second model parameter with the least error associated with it; and

i) reporting to a user of the apparatus the first and second model parameters selected as superior, wherein the first and second model parameters reported to the user are not necessarily obtained from the same set of curve fitting parameters.

2. Apparatus according to claim 1 wherein the electrical analog model is a second or higher order electrical analog model.

3. Apparatus according to claim 2 wherein the electrical analog model is the modified Windkessel model.

4. An apparatus according to claim 1, wherein the first and second model parameters reported to the user are not necessarily obtained from the same set of curve fitting parameters.

5. The apparatus according to claim 1, wherein the apparatus comprises a computer programmed to carry out the steps of:

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

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

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

6. 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;

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;

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

g) determining an error associated with each model parameter determined in step e in order to establish which model parameter determined in step e has the least error associated with it.

7. Apparatus according to claim 6 further wherein the electrical analog model has at least two parameters associated with it each representing different aspects of the vasculature, and wherein the computer is programmed to perform the following steps:

h) for each of the two or more different model parameters, identifying which one of the model parameters determined in step g has the least error associated with it and associating the identified model parameters with the waveform being processed, wherein a first identified parameter may be obtained from a first diastolic data set of the diastolic waveform and a second identified parameter may be obtained from a different diastolic data set of the diastolic waveform.

8. Apparatus according to claim 6 wherein the electrical analog model is a second or higher order electrical analog model.

9. Apparatus according to claim 8, wherein the electrical analog model is the modified Windkessel model.

10. The apparatus according to claim 6, wherein the apparatus comprises a computer programmed to carry out the steps of:

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

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

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

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

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

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

c) 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;

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

e) selecting as superior the first model parameter with the least error associated with it;

f) determining a second model parameter of an electrical analog model of the 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 second model parameters;

h) selecting as superior the second model parameter with the least error associated with it; and

i) reporting to a user of the apparatus the first and second model parameters selected as superior, wherein the first and second model parameters reported to the user are not necessarily obtained from the same set of curve fitting parameters.

12. A method according to claim 11, wherein the electrical analog model is a second or higher order electrical analog model.

13. A method according to claim 12, wherein the electrical analog model is the modified Windkessel model.

14. The method according to claim 11, wherein analyzing a digitized arterial blood pressure waveform using a computer comprises:

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

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

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

15. 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;

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

g) determining an error associated with each model parameter determined in step e in order to establish which model parameter determined in step e has the least error associated with it.

16. A method according to claim 15, further wherein the electrical analog model has at least two parameters associated with it each representing different aspects of the vasculature, and including the additional step of:

h) for each of the two or more different model parameters, identifying which one of the model parameters determined in step g has the least error associated with it and associating the identified model parameters with the waveform being processed, wherein a first identified parameter may be obtained from a first diastolic data set of the diastolic waveform and a second identified parameter may be obtained from a different diastolic data set of the diastolic waveform.

17. A method according to claim 15, wherein the electrical analog model is a second or higher order electrical analog model.

18. A method according to claim 17, wherein the electrical analog model is the modified Windkessel model.

19. The method according to claim 15, wherein analyzing a digitized arterial blood pressure waveform using a computer comprises:

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

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

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

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

a) marking a point representative of the onset of diastole;

b) marking a point representative of the end of diastole, the end of diastole determined by locating the point where the waveform ceases monotonic decay; and

c) determining the point at which the waveform ceases to decay monotonically by finding the point at which the waveform changes at less than about a 0.1% rate.

21. Apparatus for identifying a diastolic portion of a digitized arterial blood pressure waveform comprising a computer programmed to carry out the steps of:

a) marking a point representative of the onset of diastole; and

b) marking a point representative of the end of diastole, the end of diastole determined by locating the point where the waveforn ceases monotonic decay,

wherein the point at which the waveform ceases to decay monotonically is determined by finding the point at which the waveform changes at less than about a 0.1% rate.

22. Apparatus for identifying a diastolic portion of a digitized arterial blood pressure waveform comprising a computer programmed to carry out 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; and

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

23. Apparatus according to claim 22, wherein the point at which the waveform ceases to decay monotonically is determined by finding the point at which the waveform changes at less than about a 0.1% rate.