Validation of noninvasive maximal cardiac output measurement

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Abstract
Due to the invasiveness of direct techniques and problems that constrain the use of popular indirect techniques during very heavy (non-steady-state) exercise, measurements of maximal caridac out-put are seldom included in studies of exercise. The acetylene-rebreathing technique is well-suited for maximal exercise: however, until recent technological advances, difficulties involved in collecting and measuring alveolar acetylene samples have restricted its use. Cardiac output values measured via the acetylene-rebreathing technique (.ovrhdot.QA) (modified for use with a mass spectrometer) and the dye-dilution technique (.ovrhdot.QD) at rest and during light were compared to maximal exercise in 6 moderately active males. Although .ovrhdot.QA consistently underestimated .ovrhdot.QD, the 2 techniques showed a significant correlation of 0.87 throughout all levels of exercise. During maximal exercise, .ovrhdot.QA and .ovrhdot.QD values were not significantly different (24.7 and 26.7 l .cntdot. min-1, respectively). Modifications in the .ovrhdot.QA technique that reduce potential sources of error were also examined. The acetylene-rebreathing technique, modified for use with a mass spectrometer, is a simple and valid procedure for measuring maximal cardiac output.