Apparatus and method for measuring cardiac output

摘要

A thermodilution cardiac output computer uses an autobalancing temperature-measuring circuit which adjusts the initial voltage derived from a thermistor and then holds constant the current through the thermistor as the thermistor responds to different temperatures in a blood-injectate mixture. The initial voltage is adjusted to a predetermined constant so that the response from thermistors of different initial resistance is the same. A Wheatstone bridge is not used. Before the temperature measurement, the voltage derived from the thermistor is adjusted to be equal to a predetermined constant either by varying the current through the thermistor or, with a constant current through the thermistor, by varying the gain of the amplifier sensing the voltage across the thermistor. During the temperature measurement this current or gain is held constant. The voltage change derived from the thermistor is integrated in a conventional integrator, and the integration is stopped at the tail of the decay of the temperature-time curve by an automatic timer. This termination point is calculated not as a percentage of the peak value of the curve or at a particular slope of the curve, but as a function of the time of two points high on the decay curve where the artifacts causing undulations in the curve are small compared to the temperature height of the curve. In this fashion, the triggering of the cutoff point by undulations in the curve is avoided.