Journal of Applied Physiology, Vol 40, Issue 2 266-268, Copyright © 1976 by American Physiological Society
On-line cardiac output by digital computer
F. Huber, I. E. Sodal and J. V. Weil
Many devices for fast cardiac output calculations employ special
assumptions and departures from the Stewart-Hamilton method. These
assumptions and departures can cause substantial errors. This publication
describes an on-line computer system for evaluating dye-dilution curves
according to the classical Stewart-Hamilton method. Dilution curves are
smoothed, using a digital filter to eliminate heartbeat noise.
Recirculation is removed using the constant ratio property of exponentials.
The quality of the curves is evaluated by determining the length of the
base line, the extent and the fit to an exponential downslope, and a figure
of merit based on the five tanks-in-series model. Dilution curves, the
logarithmic form, and the exponential ratios are displayed on a CRT for
visual checks. Comparison of cardiac outputs obtained by this on-line
system with results obtained by hand calculations showed a mean difference
of 150 ml. Repeated evaluation of one electronically simulated dye curve
resulted in SD = 10 ml for computer results and SD = 200 ml for hand
calculations.
