Persistent peripheral vasodilation and sympathetic activity in hypotension after maximal exercise

Abstract

Hemodynamics (by aortic Doppler), autonomic factors (power spectrum analysis 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 days: a nonexercise (control) day (30 min of upright rest followed by 60 min of supine rest) and an exercise day (maximal upright bicycle exercise followed by 60 min supine) in random order. After exercise, diastolic pressure was reduced for the entire hour, cardiac output increased (+33.8%, P < 0.05), stroke volume was unchanged, and systemic vascular resistance fell (-28.6%, P < 0.01). Indexes of vagal activity were reduced for 60 min, whereas the sympathetic indexes were elevated. Baroreflex sensitivity was also reduced for the first 10 min after exercise. Renin activity increased threefold after exercise. The postexercise hypotension results from a persisting peripheral vasodilation despite an increase in renin activity: the persistent sympathetic activity and reduced vagal tone are probably reflex responses to this vasodilatation.

Potential causes, mechanisms, and implications of post exercise hypotension

“…In both normotensive 33,63 and borderline hypertensive 38,39 individuals, these indirect indices suggest that sympathetic outflow is increased over the same interval in which PEH is observed. This may be a reflexive response to partially offset the exercise induced hypotension.…”

“…In those studies that have observed a decline in blood pressure following exercise, the average decrement in pressure was approximately 8/9 (SBP/DBP) mm Hg in the normotensive population, 16,[20][21][22][23]25,[31][32][33][34][35] 14/9 mm Hg in the borderline hypertensive population [10][11][12]34,[36][37][38][39] and 10/7 mm Hg in the hypertensive population. 13 37 We recently examined the effects of the exercising muscle mass by comparing the PEH response to both leg and arm ergometry at the same relative intensity.…”

“…10,11,19,22,24,[31][32][33]35,41,[43][44][45][59][60][61]63,71,72 Treadmill exercise at similar intensities has also been documented to elicit PEH. 14,15,20,25,34,40,[55][56][57][58] Direct comparisons of the effect of exercise intensity have, for the most part, found that PEH occurs independent of exercise intensity.…”

“…The onset of hypotension following exercise has been found to occur within the initial minutes after exercise 33,72,79 or at some time point between 30 min and 1 h following exercise. 9,16,31,44,49,57,61 Most studies have measured blood pressure for only 1-2 h following exercise 12,13,16,20,22,23,25,34,[36][37][38][39]55,58,75 and the majority of these have found a nadir in blood pressure during that time with a return or trend towards baseline pressure at the cessation of measurement.…”

“…13,15,57 In all such instances the decrements were found to be due to reductions in stroke volume. In humans, it is common to observe an increased heart rate during some or all of the hypotensive period, 20,22,33,35,58,63,77 whereas rodents often display decreased or unchanged heart rates. 30,[48][49][50]54 Of interest is that, with the exception of one study, 43 changes in human cardiac output post exercise appear dependent on the initial state of hypertension.…”