Simplified Calculation of Cardiac Output From Dye Dilution Curves Recorded by Oximeter

Abstract

Dye dilution curves recorded by cuvette oximeters were reduced empirically to triangles by drawing straight lines through the ascending and descending limbs of the curves. Values related to mean concn. of dye and dye passage time could than be measured directly from the record and calculation of cardiac output completed within a few min. Use of the triangle method for calculation of cardiac output from dye dilution curves recorded by cuvette oximeter increased the inherent variability of the dye method from approx. 11-14%. Cardiac output also was calculated from dye curves recorded with an ear oximeter by using a mean value for sensitivity to dye detd. by simultaneously recording earpiece and cuvette oximeter dye curves. The mean value for cardiac output detd. from earpiece dye curves by the triangle method did not differ from the mean obtained from simultaneously recorded cuvette oximeter curves by the replot method (32 subjects) or from the mean of almost simultaneous direct Fick values on 15 patients with mitral stenosis. The standard deviations of the differences between earpiece and cuvette and earpiece and direct Fick detns. were, however, 17 and 26%, resp. The accuracy of the method, although leaving much to be desired, is still of an order suitable for use in certain clinical and exptl. situations. Further improvements in oximeter design may considerably reduce the degree of variability which has been found.