Measurement of cardiac output by earpiece dye-dilution method with automatic calibration of dye concentration.

A non-invasive method for measuring cardiac output by an earpiece dye densitometer was proposed. The densitometer is dichromatic and has an air capsule to make subject's ear bloodless by inflation, so that it can calibrate indocyanine green dye concentration without blood sampling. Duplicate measurements of cardiac output showed a good agreement in 40 cases (r = 0.97, standard deviation (S.D.) = 8.9%), which was comparable to the result of the cuvette method (r = 0.98, S.D. = 8.1%). Simultaneous measurements of cardiac output by the earpiece method (x) and the standard cuvette method (y) revealed a good agreement (r = 0.91, y = 0.96x+0.34, S.D. = 16.4%) in 52 measurements of 25 cases. A similarly good correlation was obtained between the two methods during ergometer exercise in supine position in 5 cases. These suggest that this earpiece dye-dilution method is reliable for cardiac output measurement and advantageous for clinical use because of non-invasive technique.