USE OF DICHROMATIC EARPIECE DENSITOMETRY FOR DETERMINATION OF CARDIAC OUTPUT

Dye-dilution curves were recorded simultaneously by a monochromatic earpiece densitometer, a dichromatic earpiece densitometer and a cuvette densitometer through which blood was sampled continuously from a radial artery. Comparison of cardiac output values were made using the direct coupled arterial cuvette as a standard in nine healthy subjects during three periods of rest and during two periods of pedalling a bicycle ergometer at different levels of work output. Data are also included from similar studies carried out in five cardiac patients in whom no great vessel or intracardiac shunts could be demonstrated. The results showed a high degree of variability for the monochromatic earpiece densitometer values standard deviation of differences 31 because of baseline variations due to changing conditions in the ear. The dichromatic earpiece densitometer which compensates for dynamic changes in the ear showed satisfactory comparison with arterial cuvette densitometer standard deviation of differences 14. The dichromatic earpiece densitometer showed a linear relationship between its calibration factor for dye centimeters deflectionmilligrams dyeliter of blood and the relative blood content of the ear. A dichromatic ear densitometer appears feasible for estimating cardiac output where use of more direct methods is precluded.