Apparatus and methods for the noninvasive measurment of cardiovascular system parameters
First Claim
1. A method of noninvasively measuring cardiac output of a living subject, comprising the steps of:
- measuring systolic minus diastolic pulse pressure of the subject;
measuring the heart rate of the subject;
computing the cardiac output of the patient from the following equation;
space="preserve" listing-type="equation">CO=HR*PP*C*0.133 where CO is cardiac output in liters/minute;
HR is the measured heart rate in beats/minutes;
PP is the measured systolic minus diastolic pulse pressure in mmHg;
0.133 is a conversion factor; and
C is a capacitance value representative of arterial compliance, wherein C has a magnitude of about
space="preserve" listing-type="equation">C=X*10.sup.-6 Farads,and X is a function of one or more of pulse pressure, age in years, height in centimeters, and weight in kilograms.
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Abstract
Apparatus and methods for noninvasively measuring cardiovascular system parameters. According to a first preferred embodiment, the apparatus generates a time varying electrical voltage waveform having voltages corresponding to systolic and diastolic arterial pressures of the subject, the parameters being modelled by a lumped element electric circuit model analogous to the living subject'"'"'s cardiovascular system, said circuit model including a systolic capacitor analogous to arterial compliance during systole, said apparatus comprising means for computing the value of said systolic capacitor from a measurement of an elapsed time between two voltage levels within a portion of said voltage waveform corresponding to systole, according to a predetermined criteria; and means for computing at least one said cardiovascular system parameter from said capacitor value. According to a second embodiment, a time-varying systolic arterial compliance is measured by measuring an arterial pulse pressure waveform. A third embodiment discloses a method of measuring cardiac output noninvasively from a cuff measurement of a patient'"'"'s systolic minus diastolic blood pressure and a heart rate measurement. Cardiac output equations are derived from an unmodified Windkessel circuit model which models arterial compliance as a single lumped capacitance. General formulas for the value of the lumped capacitance are provided which are used to more accurately compute cardiac output from this circuit model.
116 Citations
19 Claims
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1. A method of noninvasively measuring cardiac output of a living subject, comprising the steps of:
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measuring systolic minus diastolic pulse pressure of the subject; measuring the heart rate of the subject; computing the cardiac output of the patient from the following equation;
space="preserve" listing-type="equation">CO=HR*PP*C*0.133where CO is cardiac output in liters/minute;
HR is the measured heart rate in beats/minutes;
PP is the measured systolic minus diastolic pulse pressure in mmHg;
0.133 is a conversion factor; and
C is a capacitance value representative of arterial compliance, wherein C has a magnitude of about
space="preserve" listing-type="equation">C=X*10.sup.-6 Farads,and X is a function of one or more of pulse pressure, age in years, height in centimeters, and weight in kilograms. - View Dependent Claims (2, 3, 4)
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5. A method of noninvasively measuring cardiac output of a living subject, comprising the steps of:
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measuring systolic minus diastolic pulse pressure of the subject; measuring the heart rate of the subject; and computing the cardiac output of the patient as a function of heart rate, the measured systolic minus diastolic pulse pressure, a constant, and a capacitance value indicative of arterial compliance, wherein said capacitance has a non-constant value and is derived from a Windkessel circuit model analog. - View Dependent Claims (6, 7, 8, 9, 10, 11, 12)
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13. An apparatus for measuring cardiac output using system parameters of a living subject, comprising:
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means for modeling the parameters of the living subject with a lumped element electric circuit model analogous to the living subject'"'"'s cardiovascular system, wherein the circuit model includes a systolic capacitor analogous to arterial compliance during systole; first transducer means for sensing a time varying arterial pressure pulse waveform from the living subject and converting said pressure pulse waveform to an electrical voltage waveform having voltages corresponding to systolic and diastolic arterial pressures of the subject; means for measuring the heart rate of the subject means for computing the value of said systolic capacitor from measurements of the living subject'"'"'s heart rate and pulse pressure; and means for computing the cardiac output from said capacitor value. - View Dependent Claims (14, 15, 16, 17, 18, 19)
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Specification