Method for vascular impedance measurement

• US 5,316,004 A
• Filed: 03/26/1993
• Issued: 05/31/1994
• Est. Priority Date: 12/28/1990
• Status: Expired due to Term

• Current Assignee: Regents of The University of Minnesota (University of Minnesota)
• Original Assignee: Regents of The University of Minnesota (University of Minnesota)
• Inventors: Cohn, Jay N., Finkelstein, Stanley M., Chesney, Charles F.
• Primary Examiner(s): Kamm, William E.
• Assistant Examiner(s): SCHAETZLE, KENNEDY
• Application Number:
  US08/038,357
• Time in Patent Office: 431 Days
• Field of Search: 128/672, 128/668, 128/691, 128/692, 128/713, 364/413.03, 364/413.02
• US Class Current: 600/485
• CPC Class Codes: A61B 5/02007 Evaluating blood vessel condition, e.g. elasticity, compliance
• CPC Class Codes: A61B 5/021 Measuring pressure in heart or blood vessels A61B5/0205 takes precedence
• CPC Class Codes: A61B 5/029 Measuring or recording blood output from the heart, e.g. minute volume A61B8/065 takes precedence
• CPC Class Codes: G09B 23/28 for medicine
• CPC Class Codes: Y10S 128/92 Computer assisted medical diagnostics

Abstract

A vascular impedance measurement instrument includes a transducer to obtain a digitized arterial blood pressure waveform. The digitized data is used to determine cardiac output, and to subsequently obtain measurements of impedance parameters using the modified Windkessel model of the arterial system. The instrument is used as an aid in diagnosing, treating and monitoring patients with cardiovascular disease.

Claims

1. A method for measuring vascular impedance properties from the blood pressure waveform of a patient, the waveform containing heart beat signals, comprising the steps of:

measuring and digitizing an arterial blood pressure of a patient to produce a series of digitized data samples representing a waveform of the arterial blood pressure of the patient;

processing a heart beat signal in the digitized blood pressure waveform, marking a segment of the heart beat signal corresponding to systole, and determining an ejection time by measuring the duration of said segment;

processing the same series to determine a mean arterial pressure of the patient;

processing said ejection time and other patient data to determine a cardiac output measurement value for the patient from at least said ejection time and other patient data; and

processing the sample series and the cardiac output value and mean arterial pressure to determine for the patient one or more parameters of a vascular impedance model, the parameters being measures of vascular impedance properties.

8. The method of claim 1, 2, 3, 4 or 7 further wherein the vascular impedance model is a modified Windkessel model of the vasculature.

9. The method of claim 1, 2, 3, 4 or 7 further wherein the vascular impedance model is a first order model of the vasculature.

2. A method for measuring vascular impedance properties from the blood pressure waveform of a patient, the waveform containing heart beat signals, comprising the steps of:

measuring and digitizing an arterial blood pressure of a patient to produce a series of digitized data samples representing a waveform of the arterial blood pressure of the patient, the waveform containing heart beat signals;

processing the heart beat signals in the digitized blood pressure waveform to select a group of representative heart beat signals, said heart beat signals selected according to predetermined criteria whereby unwanted signals are filtered out;

processing a heart beat signal in the digitized blood pressure waveform, marking a segment of the heart beat signal corresponding to systole, and determining an ejection time by measuring the duration of said segment;

processing at least said ejection time and other patient data to determine a cardiac output measurement value for the patient; and

processing the sample series, the cardiac output value and mean arterial pressure to determine for the patient one or more parameters of a vascular impedance model, the parameters being measures of vascular impedance properties.

3. A noninvasive method for measuring vascular impedance properties from the blood pressure waveform of a patient, the waveform containing heart beat signals, comprising the steps of:

noninvasively measuring an arterial blood pressure of a patient using a technique of arterial tonometry and generating a corresponding analog arterial blood pressure waveform signal;

digitizing the blood pressure waveform signal to produce a corresponding series of digitized data samples representing the waveform of the arterial blood pressure of a patient; and

processing the sample series to determine a mean arterial pressure of the patient;

processing the sample series and other patient data to determine a cardiac output measurement value for the patient; and

processing the sample series and the cardiac output measurement value and mean arterial pressure to determine for the patient one or more parameters of a vascular impedance model, the parameters being measures of vascular impedance properties.

4. A method for measuring vascular impedance properties from the blood pressure waveform of a patient, the waveform containing heart beat signals, comprising the steps of:

measuring and digitizing an arterial blood pressure of a patient to produce a corresponding series of digitized data samples representing a waveform of the arterial blood pressure of the patient;

processing the sample series to determine a cardiac output measurement value for the patient;

processing heart beat signals in the digitized blood pressure waveform, and marking segments of the heart beat signals corresponding to diastole; and

processing the marked diastolic segments of the sample series and the cardiac output value and mean arterial pressure to determine for the patient one or more parameters of a vascular impedance model, the parameters being measures of vascular impedance properties.

5. The method according to claim 4 further wherein the step of processing the sample series determine a cardiac output measurement value includes the step of determining the measurement using the ejection time of the heart as determined from the sample series.

6. The method according to claim 5 further wherein the step of processing the sample series to determine a cardiac output value includes the step of determining stroke volume substantially in accordance with the following formula:

space="preserve" listing-type="equation">SV=-6.6+(0.25×

ET)+(40.4×

BSA)-(0.51×

Age)-(0.62×

HR),

where SV equals stroke volume in ml/beat, ET is ejection time in msec, BSA is body surface area in square meters, Age is expressed in years, and HR is heart rate in beats per minute.

7. A method for processing the blood pressure waveform of a patient to determine the condition of a patient'"'"'s vasculature from the shape of certain portions of the waveform, including at least the compliance of the patient'"'"'s blood vessels, the waveform containing heart beat signals, comprising the steps of:

measuring and converting a blood pressure waveform of the patient to a corresponding analog signal;

digitizing the blood pressure waveform signal for a series of the patient'"'"'s heart beats and storing the signal in a digital storage device;

processing the digitized blood pressure waveform signal to;

(a) count the number of heart beats per unit time in the digitized blood pressure waveform to produce a heart rate signal for the patient, and

(b) search a heart beat signal in the digitized blood pressure waveform, mark events indicating a beginning and ending of systole, and determine an ejection time signal by measuring a time between the marked events;

processing the heart rate signal, the ejection time signal, and values representing the patient'"'"'s age and body surface area to generate an output signal indicative of the patient'"'"'s cardiac output;

processing the digitized blood pressure waveform and determining therefrom a mean arterial pressure signal indicative of the patient'"'"'s mean arterial pressure;

processing the digitized blood pressure waveform and marking segments of the waveform corresponding to a period of diastole in the heart; and

processing the marked segments of the digitized blood pressure waveform, the cardiac output signal and the mean arterial pressure signal, to analyze the shape of the marked diastolic segments and determine one or more signals representing a condition of the patient'"'"'s vasculature from a vascular impedance model, the one or more signals including a least a compliance signal representative of the flexibility of the patient'"'"'s blood vessels.