Simultaneous and rapidly repeated cardiac output determinations by dye-dilution method

Reproducibility of cardiac output determinations by dye dilution at rest and during graded treadmill exercise has been assessed by means of simultaneous, rapidly repeated measurements with two Waters 250-A densitometers at both a single sampling site and from both arms. A total of 232 paired-dilution curves was recorded from 10 normal subjects with both densitometers sampling from the same radial artery, and 158 curves from 9 subjects, one densitometer sampling each radial artery simultaneously. Measurements were made with subjects recumbent and during walking varying from level to a 12° treadmill elevation. With both densitometers sampling the same arterial stream cardiac output variation from the two instruments progressively increased from 7% (0.562 liter/min) at rest to 11% (2.773 liter/min) at peak exercise as represented by a standard deviation of the difference related to mean cardiac output. When two arterial streams were being sampled for each injection, variation between instruments amounted to 9–12% of mean cardiac output. Significantly greater variation was observed in curves obtained within 1 min of each other from the same densitometer. measurement of cardiac output during exercise; cardiac output technique; variation in dye-dilution technique; bilateral cardiac output measurements; upright treadmill exercise Submitted on July 12, 1963