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

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Abstract
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