Use of dichromatic earpiece densitometry for determination of cardiac output.

after injection of 5 mg of indocyanine green into the superior vena cava of 14 subjects during rest and exercise were recorded by a dichromatic ear densitometer, a conventional ear oximeter used as a monochromatic densitometer, and a cuvette coupled to the radial artery. Calibration of earpieces assumed linearity for extrapolation of the deflection at 90 set after injection on the basis of dye concentration estimated from hematocrit and spectrophotometry of plasma samples from the radial artery and arm vein. With the cuvette as a reference, cardiac output values gave no systematic variation when calibrated from arterial blood. The standard deviation of differences by ear oximeter was 31 y0 and by dichromatic ear densitometer 14y0. The dichromatic ear densitometer showed a linear relationship between its calibration factor for dye (cm deflection/mg dye per liter of blood) and the relative blood content of the ear