The Use of the Ear Oximeter for Measurement of the Cardiac Output During Walking Exercise in Human Subjects ‡

For the study of walking exercise in human subjects, an accurate method for measurement of the cardiac output is needed which can be applied repeatedly and with minimal discomfort to the subject. Continuous recording of dye-dilution curves by means of an ear oximeter has been used previously,"'9'10 for estimating the cardiac output at rest, and requires only venipuncture. However, the accuracy of this method has been seriously questioned for the following principal reasons: a. Dye-dilution curves obtained from the ear frequently differ in form from those obtained simultaneously from a systemic artery. b. The presently available commercialif earpiece has been used in prior studies without full consideration of the photometric characteristics of the earpiece system. c. Methods for the calibration of earpiece curves, in terms of mg. per cent of dye in arterial blood per cm. of galvanometer deflection, have been inadequate.