Estimates of cardiac output from forward part of indicator dilution curves

¹ Cardiopulmonary Research Unit, Department of Physiology, University of Sydney, Sydney, Australia

A study was made of 135 dye-dilution curves, 77 of which were obtained from dogs and 58 from man. It was previously shown that the degree of asymmetry of indicator dilution curves varies with changes in flow, volume, and path length, and this has been found to influence the estimates of cardiac output made from the initial part of the curves by the forward triangle and Dow methods, and by a new method described in this paper. This variation may be minimized by the calculation of separate constants for each injection site and by keeping the variation in flow and volume as small as possible. Errors are likely to arise when these methods are used outside the range of the normal data. It has been found that this variation in asymmetry is mainly responsible for the scatter in the estimates of cardiac output using these methods. The agreement between the forward triangle and the Dow methods was found to be very close and the reason for this is discussed.