[Kinetics of adjustment of cardiac output to muscular exertion].

The kinetics of oxygen uptake (VO2), cardiac output (Q), and heart rate (HR) were studied in three healthy male subjects during onset of exercises up to 750 kpm/min. VO2 was measured on a single breath basis, Q by CO2-N2 rebreathing method at 30" intervals from time 0 to 6 min of exercise, and HR beat by beat. In the transition from rest to exercise, the increase of Q and VO2 follows a single exponential function, while h. r. a double exponential. Average half times of Q and VO2 during the onset of exercise are about 18" and 26" respectively. Q changes seem to anticipate VO2 changes at the first 15-45 s of exercise, while thereafter a proportional increase is observed. This non-linear increase of Q to VO2 at the beginning of exercise may presumably be due to a neurogenic control of h.r. and hence of Q from receptors at muscular level.