Method and apparatus for measuring cardiac output
First Claim
1. A method for measuring cardiac output (CO) of a patient comprising the following steps:
- sensing arterial blood pressure and converting the sensed arterial blood pressure to a pressure signal;
calculating an estimate of stroke volume as a function only of selected characteristics of the sensed pressure signal and of predetermined, patient unspecific constants; and
calculating an estimate of CO as a function of the estimated stroke volume and a current heart rate value.
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Abstract
Cardiac stroke volume and output are estimated using an arterial pressure signal, which may be obtained either invasively, using a catheter-mounted pressure sensor, or non-invasively, with an external plethysmographic sensor mounted with a finger cuff. Both pulsatile and non-pulsatile (continuous) components of the sensed pressure signal are analyzed. Stroke volume is estimated as a function of the ratio between the area under the entire pressure curve and a linear combination of various components of impedance. Depending on the embodiment, first and/or second time derivatives of the pressure signal are used to determine the impedance components. The estimated stroke volume is preferably corrected based on the amount of deviation from a reference pressure of the mean pressure, which itself is determined from the sensed pressure signal. The invention is thus able to estimate stroke volume and cardiac output from the pressure signal alone, with no need for calibration using other highly invasive techniques.
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Citations
23 Claims
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1. A method for measuring cardiac output (CO) of a patient comprising the following steps:
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sensing arterial blood pressure and converting the sensed arterial blood pressure to a pressure signal;
calculating an estimate of stroke volume as a function only of selected characteristics of the sensed pressure signal and of predetermined, patient unspecific constants; and
calculating an estimate of CO as a function of the estimated stroke volume and a current heart rate value. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 17, 18, 20, 21, 22)
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16. A method for measuring cardiac output (CO) of a patient comprising the following steps:
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sensing arterial blood pressure and converting the sensed arterial blood pressure to a pressure signal;
calculating an area under the entire pressure signal, including both pulsatile and non-pulsatile portions of the pressure signal, over a cardiac cycle;
estimating selected impedance values from the pressure signal;
calculating a mean pressure value of the pressure signal;
calculating an estimate of stroke volume as a function only of selected characteristics of the sensed pressure signal and of predetermined constants, including, the selected characteristics including the ratio between the calculated area and the estimated selected impedance values; and
calculating an estimate of CO as a function of the corrected, estimated stroke volume and a current heart rate value;
in which the pressure signal is uncalibrated, whereby the steps of calculating the estimate of the stroke volume of calculating the estimate of CO are independent of external calibration.
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19. A system for measuring cardiac output (CO) of a patient comprising:
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pressure sensing means for sensing arterial blood pressure;
signal processing means for converting the sensed arterial blood pressure to a pressure signal;
processing means;
for calculating an estimate of stroke volume as a function only of selected characteristics of the sensed pressure signal and of predetermined constants; and
for calculating an estimate of CO as a function of the estimated stroke volume and a current heart rate value.
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23. A computer-readable medium having computer-executable instructions for performing steps for measuring cardiac output (CO) of a patient comprising the following steps:
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sensing arterial blood pressure and converting the sensed arterial blood pressure to a pressure signal;
calculating an estimate of stroke volume as a function only of selected characteristics of the sensed pressure signal and of predetermined, patient unspecific constants; and
calculating an estimate of CO as a function of the estimated stroke volume and a current heart rate value.
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Specification