Computer measurement of cardiac output by dye dilution: comparison of computer, Fick, and Dow techniques

Abstract

Seventy-five indocyanine green dye curves were done in 27 patients, with Fick cardiac output determinations being carried out just before the dye curves. A digital computer was programmed to calculate dye cardiac output by the method of Hamilton, using four different segments of the washout portion of the curves to approximate an exponential and exclude recirculation. Comparison of computer determinations with those done manually revealed remarkably similar results for all four programmes with a standard deviation of the difference of approximately 6%. Considerations of ease of programming and economy of calculations, as well as accuracy of the results, have led to selection of two of the programmes as providing the most effective method of analysis. Computer Hamilton analysis and the Dow formula were compared with the Fick in the entire patient population and in those patients with reduced cardiac output. The Dow formula produced significantly more scatter than the Hamilton technique in both normal and low output states; there was no consistent underestimation of cardiac output by the dye method in low output states, nor when the distance between injection site and sampling site was maximized. Analysis of dye curves by digital computer provides a rapid and accurate method for multiple cardiac output determinations.