Serial determinations of cardiac output at rest.

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Abstract
Cardiac output was determined in a group of healthy volunteers, age range 21-39 years, using the dye-dilution technique with Cardio-green as an indicator, a direct recording system, and reinfusion of the flood after each recording. Ten determinations at 5-min. intervals gave a mean cardiac index in 14 subjects of 3.18 1 min. m2. The average coefficient of variation was 8.6%. Thereafter 2 determinations were made during the collection of expired air. No systematic change occurred during the 45-min. period, but when the subjects breathed through the mouthpiece for determination of O2 uptake there was a small (6%) increase in cardiac output. An example is also given of experiments where disturbances caused a more marked variation in cardiac output. The technique used in this investigation is well suited for studies where changes in cardiac output have to be followed with repeated determinations.