Estimation of Cardiac Output in Man Using an Ear Oximeter and Coomassie Blue Dye

A method of measuring cardiac output from dyedilution curves recorded by an ear oximeter is described. No sampling of blood is necessary to make the dye-dilution curves quantitative. The inaccuracies inherent in the "end-tail" method of calibration are thus avoided and the technical procedure greatly simplified. Theoretical considerations, circuitry and calibration procedures are discussed. Forty-one cardiac output estimations were made in 15 subjects. Coomassie blue was used as indicator. Comparison was made between the results obtained by the technique under study and by the end-tail venous method. Seven results had to be excluded from the comparison due to manifest inaccuracy of the reference method, which is inherently inaccurate. In spite of this, there was reasonably good agreement. The standard deviation of the differences between simultaneous values by both methods was 14.3 per cent. Fifty-two dye-dilution curves were recorded in seventeen white subjects at rest and during steady-state exercise at loads up to 600 kilogram-meters per minute. Comparison was made between the cardiac output estimates obtained by the technique described and by the "arterial end-tail" method. The standard deviation of the differences between the simultaneous values from the two methods was 14.2 per cent.