(1) A comparative study on determination of cardiac output by simultaneously recorded earpiece and brachial arterial cuvette curves was made on 23 subjects, both in resting state and during leg-exercise on a bicycle ergometer.
(2) The values for resting cardiac output were well agreed in both methods, with close correlation and no deviation of regression line from unity.
(3) Relative cardiac output during exercise determined by both methods were compared in terms of percentage value of the reciprocal of area under the curves, in comparison to each resting value. Close correlation was again obtained between the values by the 2 methods. Although there was a minor tendency for less increases in cardiac output by the earpiece method during exercise, the difference between the values by the 2 methods was small enough to be disregarded for the practical purpose. The physiological reaction of the ear capillaries to exercise may be suggested to contribute in part to this difference.
(4) It was concluded that with the use of a reliable equipment and with careful preparations before procedure, the earpiece indicator-dilution technique offers a potential promise in evaluation of the central circulation of the human beings in both resting and working state.