APPARATUS FOR CALCULATING CARDIAC OUTPUT

摘要

The invention provides apparatus for measuring the flow rate of liquid being circulated in a closed system by a pump using a bolus of indicator injected suddenly into the system upstream of the pump and a sampling station downstream of the pump. The apparatus includes signal means for location at the sampling station and adapted to provide an electrical signal proportional to the concentration of the indicator passing said station, the electrical signal having an increasing portion followed by a decaying exponential portion and a distorted portion caused by recirculation of the indicator. A signal analyzer is coupled to said signal means to receive said electrical signal and is adapted to provide a continuous output during the whole of said electrical signal corresponding to said increasing portion and said decaying exponential portion and including an extrapolated exponential portion replacing said distorted portion of the signal. The signal analyzer includes means to automatically zero said signal on a time base and a curve generator for receiving said signal from the zeroing means. The curve generator includes a capacitor which is charged by said signal while the signal is increasing and the curve generator is adapted to continuously compare the charge on said capacitor with said signal and to permit said capacitor to discharge exponentionally after said signal has reached a peak, at a rate matched to the decay rate of the electrical signal, said discharge rate continuously following the signal exponential decay rate. The signal analyzer also includes trigger means coupled to the curve generator and responsive to the charge on the capacitor, said trigger means being adapted to isolate the curve generator from said electrical signal when said charge on said capacitor has fallen to a predetermined level corresponding to a time during said exponential portion of said electrical signal and in advance of said distorted portion, whereby the signal analyzer output thereafter decays exponentially without interference from said distorted portion of the electrical signal. The apparatus also includes integrator means receiving said continuous signal analyzer output and adapted to integrate said output and provide a reading of the flow rate of the liquid.