Methods and apparatus for determining cardiac output

摘要

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.

主权项

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 includes
constructing 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; anddetermining cardiac output to within a constant scale factor using the time constant.