Determination of Relative Changes in Cardiac Output from Noncalibrated Earpiece Dye-Dilution Curves

• The usual methods for the measurement of changes in cardiac output involve arterial puncture; it would be of value if a technique could be used without involving this proce-dure. Coomassie Blue dye and the photoelectric earpiece1"3 make it comparatively simple to obtain successive dye-dilution curves without arterial puncture. If the response of the re-cording system is linear to blood dye concen-tration and the vascular content of the ear is constant, it should be possible to measure relative changes in cardiac output without calibrating the corves. The purpose of this paper is to investigate the validity of using noncalibrated earpiece dye-dilntion curves for such measurements in man. Arterial cu-vette curves were used as the standard of comparison, and simultaneous earpiece curves were recorded during changes in posture, ex-ercise, and intravenous administrations of an antihypertensive agent (guanethidine), so-dium amobarbital, and norepinephrine