PERSISTENT PERIPHERAL VASODILATION AND SYMPATHETIC ACTIVITY IN HYPOTENSION AFTER MAXIMAL EXERCISE

Hemodynamics (by aortic Doppler), autonomic factors (power spectrum an alysis of heart rate and blood pressure variabilities and baroreceptor sensitivity), and plasma renin activity during the hypotension after maximal exercise were studied in 10 normal subjects on two separate da ys: a nonexercise (control) day (30 min of upright rest followed by 60 min of supine rest) and an exercise day (maximal upright bicycle exer cise followed by 60 min supine) in random order. After exercise, diast olic pressure was reduced for the entire hour, cardiac output increase d (+33.8%, P < 0.05), stroke volume was unchanged, and systemic vascul ar resistance fell (-28.6%, P < 0.01). Indexes of vagal activity were reduced for 60 min, whereas the sympathetic indexes were elevated. Bar oreflex sensitivity was also reduced for the first 10 min after exerci se. Renin activity increased threefold after exercise. The postexercis e hypotension results from a persisting peripheral vasodilatation desp ite an increase in renin activity: the persistent sympathetic activity and reduced vagal tone are probably reflex responses to this vasodila tation.