IMPAIRED SYMPATHETIC VASCULAR REGULATION IN HUMANS AFTER ACUTE DYNAMIC EXERCISE

1. The reduction in vascular resistance which accompanies acute dynami c exercise does not subside immediately during recovery, resulting in a post-exercise hypotension. This sustained vasodilatation suggests th at sympathetic vascular regulation is altered after exercise. 2. There fore, we assessed the baroreflex control of sympathetic outflow in res ponse to arterial pressure changes, and transduction of sympathetic ac tivity into vascular resistance during a sympatho-excitatory stimulus (isometric handgrip exercise) after either exercise (60 min cycling at 60% peak aerobic power (V-O2,V-peak) or sham treatment (60 min seated rest) in nine healthy subjects.3. Both muscle sympathetic nerve activ ity and calf vascular resistance were reduced after exercise (-29.7+/- 8.8 and -25.3+/-9.1%, both P<0.05). The baroreflex relation between di astolic pressure and sympathetic outflow was shifted downward after ex ercise (postexercise intercept, 218+/-38 total integrated activity (he artbeat)(-1); post-sham intercept, 318+/-51 total integrated activity (heartbeat)(-1), P<0.05), indicating less sympathetic outflow across a ll diastolic pressures. Further, the relation between sympathetic acti vity and vascular resistance was attenuated after exercise (post-exerc ise slope, 0.0031+/-0.0007 units (total integrated activity)(-1) min; post-sham slope, 0.0100+/-0.0033 units (total integrated activity(-1) min, P<0.05), indicating less vasoconstriction with any increase in sy mpathetic activity. 4. Thus, both baroreflex control of sympathetic ou tflow and the transduction of sympathetic activity into vascular resis tance are altered after dynamic exercise. We conclude that the vasodil atation which underlies post-exercise hypotension results from both ne ural and vascular phenomena.