Intersubject variability in cardiac output-O2 uptake relation of men during exercise

Intersubject variability in the relation between cardiac output (Q) and O2 uptake (VO2) was examined during supine cycling up to the maximum level in 40 normal untrained men age 27 +/- 4 (SD) yr. In individual subjects, Q increased linearly against VO2 in the submaximum exercise range. The SD of Q on VO2 was so small (0.47 +/- 0.25 l/min) that Q could be given by a linear function of VO2 as Q = K(VO2 - VO2 r) + Qr, where K, VO2 r, and Qr are the slope of the regression line, the resting VO2, and resting Q, respectively. K varied widely among the subjects studied, ranging from 5.5 to 10.3 and was independent of both physical characteristics and Qr, which ranged from 3.7 to 8.3 l/min. However, K correlated significantly with changes in heart rate, stroke volume, mean arterial pressure, and systemic vascular conductance. From these results, we concluded that the intersubject variability in the Q-VO2 relation was caused independently by individual variations in resting hemodynamics and in cardiovascular response to exercise.