Methods and apparatus for determining cardiac output
First Claim
1. A method for determining cardiac output to within a constant scale factor, comprising:
- measuring a physiological signal of a patient using a sensor, the physiological signal indicative of cardiovascular system activity and measured over a plurality of cardiac cycles;
determining, from the physiological signal, beat-to-beat variability of the physiological signal across multiple cardiac beats;
determining cardiac output to within a constant scale factor using the beat-to-beat variability information extracted from the physiological signal; and
presenting the cardiac output on a display of a computing device;
wherein determining beat-to-beat variability includesconstructing a cardiac contractions timing signal from the physiological signal by forming an impulse train in which each impulse is located at the onset of upstroke of each pulse;
determining an impulse response, which when convolved with the cardiac contractions timing signal, fits the physiological signal;
determining a time constant by fitting an exponential function to a tail end of the impulse response; and
determining cardiac output to within a constant scale factor using the time constant.
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Abstract
The present invention provides methods and apparatus for determining a dynamical property of the systemic or pulmonary arterial tree using long time scale information, i.e., information obtained from measurements over time scales greater than a single cardiac cycle. In one aspect, the invention provides a method and apparatus for monitoring cardiac output (CO) from a single blood pressure signal measurement obtained at any site in the systemic or pulmonary arterial tree or from any related measurement including, for example, fingertip photoplethysmography.
According to the method the time constant of the arterial tree, defined to be the product of the total peripheral resistance (TPR) and the nearly constant arterial compliance, is determined by analyzing the long time scale variations (greater than a single cardiac cycle) in any of these blood pressure signals. Then, according to Ohm'"'"'s law, a value proportional to CO may be determined from the ratio of the blood pressure signal to the estimated time constant. The proportional CO values derived from this method may be calibrated to absolute CO, if desired, with a single, absolute measure of CO (e.g., thermodilution). The present invention may be applied to invasive radial arterial blood pressure or pulmonary arterial blood pressure signals which are routinely measured in intensive care units and surgical suites or to noninvasively measured peripheral arterial blood pressure signals or related noninvasively measured signals in order to facilitate the clinical monitoring of CO as well as TPR.
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Citations
21 Claims
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1. A method for determining cardiac output to within a constant scale factor, comprising:
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measuring a physiological signal of a patient using a sensor, the physiological signal indicative of cardiovascular system activity and measured over a plurality of cardiac cycles; determining, from the physiological signal, beat-to-beat variability of the physiological signal across multiple cardiac beats; determining cardiac output to within a constant scale factor using the beat-to-beat variability information extracted from the physiological signal; and presenting the cardiac output on a display of a computing device;
wherein determining beat-to-beat variability includesconstructing a cardiac contractions timing signal from the physiological signal by forming an impulse train in which each impulse is located at the onset of upstroke of each pulse; determining an impulse response, which when convolved with the cardiac contractions timing signal, fits the physiological signal; determining a time constant by fitting an exponential function to a tail end of the impulse response; and determining cardiac output to within a constant scale factor using the time constant. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. A method for determining a dynamical property of the systemic or pulmonary arterial tree, comprising:
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measuring a physiological signal of a patient using a sensor, the physiological signal indicative of cardiovascular system activity over a plurality of cardiac cycles; determining the timing of cardiac contractions in relation to each other, which occur in a sequence of cardiac contractions, where the determination is made from the physiological signal; determining, from the timing of cardiac contractions and the physiological signal, a mathematical relationship between the timing of cardiac contractions in the sequence and the physiological signal occurring over the plurality of cardiac cycles; determining a dynamical property of the systemic or pulmonary arterial tree using the relationship; determining at least one of cardiac output and vascular resistance from the dynamical property; and presenting the at least one of cardiac output and vascular resistance on a display of a computing device. - View Dependent Claims (10, 11, 12, 13, 14)
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15. A method for determining cardiac output to within a constant scale factor, comprising:
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measuring a physiological signal of a patient using a sensor, the physiological signal indicative of cardiovascular system activity and measured over a plurality of cardiac cycles; modeling the physiological signal as an output of a mathematical function; determining an input to the mathematical function from the physiological signal, where the input is indicative of cardiac contractions; identifying the mathematical function, which when applied to the input, fits the measured physiological signal over a plurality of cardiac cycles; determining cardiac output to within a constant scale factor from the identified function; and presenting the cardiac output on a display of a computing device. - View Dependent Claims (16, 17, 18, 19, 20, 21)
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Specification