Vascular impedance measurement instrument

• US 5,211,177 A
• Filed: 12/28/1990
• Issued: 05/18/1993
• Est. Priority Date: 12/28/1990
• Status: Expired due to Term

• Current Assignee: Regents of The University of Minnesota The A Non-Profit Organization of MN
• 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:
  US07/635,278
• Time in Patent Office: 872 Days
• Field of Search: 128/713, 128/691, 128/692, 128/672, 128/668, 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. Apparatus for measuring vascular impedance properties from the blood pressure waveform of a patient, the waveform containing heart beat signals, comprising:

means for measuring an arterial blood pressure of a patient and producing a corresponding series of digitized data samples representing a waveform of the arterial blood pressure of the patient;

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

means for determining a mean arterial pressure of the patient from the sample series;

means for receiving said ejection time for determining a cardiac output measurement value for the patient from at least said ejection time and other patient data;

means for determining for the patient one or more parameters of a vascular impedance model from the sample series and from the cardiac output value and mean arterial pressure, the parameters being measures of vascular impedance properties; and

means for reporting the one or more parameters.

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

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

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

means for measuring an arterial blood pressure of a patient and producing a corresponding series of digitized data samples representing a waveform of the arterial blood pressure of the patient;

heart beat signal selection means for selecting a group of representative heart beat signals from the digitized blood pressure waveform, said heart beat signals selected according to predetermined criteria whereby unwanted signals are filtered out;

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

means for determining a mean arterial pressure of the patient from the sample series;

means for receiving said ejection time for determining a cardiac output measurement value for the patient from at least said ejection time and other patient data;

means for determining for the patient one or more parameters of a vascular impedance model from the sample series and from the cardiac output value and mean arterial pressure, the parameters being measures of vascular impedance properties; and

means for reporting the one or more parameters.

3. Noninvasive apparatus for measuring vascular impedance properties from the blood pressure waveform of a patient, the waveform containing heart beat signals, comprising:

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

digitization means for producing a corresponding series of digitized data samples representing the waveform of the arterial blood pressure of the patient;

means for determining a mean arterial pressure of the patient from the sample series;

means for determining a cardiac output measurement value for the patient from the sample series and from other patient data;

means for determining for the patient one or more parameters of a vascular impedance model from the sample series and from the cardiac output measurement value and mean arterial pressure, the parameters being measures of vascular impedance properties; and

means for reporting the one or more parameters.

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

means for measuring an arterial blood pressure of a patient and producing a corresponding series of digitized data samples representing a waveform of the arterial blood pressure of the patient;

means for determining a mean arterial pressure of the patient from the sample series;

means for determining a cardiac output measurement value for the patient from the sample series;

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

means for determining for the patient one or more parameters of a vascular impedance model from the marked diastolic segments of the sample series and from the cardiac output value and mean arterial pressure, the parameters being measures of vascular impedance properties; and

means for reporting the one or more parameters.

5. An apparatus according to claim 4 further wherein the means for determining a cardiac output measurement value includes means for determining the measurement using the ejection time of the heart as determined from the sample series.

6. The apparatus of claim 5 further wherein the means for determining a cardiac output value includes means for 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. Apparatus 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:

a transducer means for converting a blood pressure waveform of the patient to a corresponding analog signal;

a digital storage device;

an analog-to-digital converter means for digitizing the blood pressure waveform signal for a series of the patient'"'"'s heart beats and storing the signal in the digital storage device;

first processing means connected to the digital storage device for 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;

second processing means for receiving the heart rate signal, the ejection time signal, and values representing the patient'"'"'s age and body surface area, and for generating therefrom an output signal indicative of the patient'"'"'s cardiac output;

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

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

fifth processing means for receiving the marked segments of the digitized blood pressure waveform, the cardiac output signal and the mean arterial pressure signal, for analyzing the shape of the marked diastolic segments and for determining one or more signals representing a condition of the patient'"'"'s vasculature from a vascular impedance model, the one or more signals including at least a compliance signal representation of the flexibility of the patient'"'"'s blood vessels; and

display means responsive to the one or more signals for displaying the magnitude thereof.