Venous Pressure and Cutaneous Reactive Hyperemia in Exhausting Exercise and Certain Other Circulatory Stresses

Skin blood flow during incremental exercise in a thermoneutral and a hot dry environment

Eight physically fit men performed two incremental bicycle ergometer tests, one in an ambient temperature of 25 degrees C and the other at 40 degrees C. Oesophageal temperature (Tes) increased continuously throughout the tests up to 38.0 and 38.3 degrees C, respectively. In both environments, forearm blood flow (plethysmography) was linearly related to Tes above the Tes threshold for vasodilation, but at the heaviest work loads this relationship was clearly attenuated and therefore indicated skin vasoconstriction, which tended to be more pronounced at 25 degrees C. During recovery at 25 degrees C, in some subjects the forearm blood flow increased above the levels observed at the end of the graded exercise in spite of a decreasing Tes. Skin blood flow, measured by laser Doppler flow meter at the shoulder, was quantitatively different but, on average, seemed to reveal the same response pattern as the forearm blood flow. In spite of the higher level of skin blood flow in the heat, blood lactate accumulation did not differ between the two environments. The present results suggest that there is competition between skin vasoconstriction and vasodilation at heavy work rates, the former having precedence in a thermoneutral environment to increase muscle perfusion. During short-term graded exercise in a hot environment, skin vasoconstriction with other circulatory adjustments seems to be able to maintain adequate muscle perfusion at heavy work levels, but probably not during maximum exercise.

Partition of blood flow to the cutaneous and muscular beds of the forearm at rest and during leg exercise in normal subjects and in patients with heart failure

The purpose of this study was to determine the relative effects of various levels of exercise on blood flow to skin and muscle of the resting extremity of normal subjects and the manner in which this distribution is modified by congestive heart failure. Blood flow to the skin and muscle of the forearm was determined plethysmographically with the aid of epinephrine iontophoresis at rest and during supine leg exercise in 12 normal subjects and in 9 patients with failure. In normal resting subjects, forearm blood flow averaged 6.30 ml/min/100 ml, 52% partitioned to muscle and 48% to skin. In the patients, forearm blood flow averaged 2.94 ml/min/100 ml, with 48% to muscle and 52% to skin. In normal subjects performing mild exercise, forearm muscle flow was not significantly changed, but during moderate and strenuous activity it was significantly reduced. Cutaneous blood flow, however, declined early at all levels of exertion. In the normal subjects, cutaneous hyperemia occurred late during moderate exercise but with strenuous exercise, was delayed until after exercise had been discontinued. In contrast, in the patients, forearm muscle blood flow decreased strikingly during leg exercise, cutaneous flow fell and remained depressed during the entire period of exercise, and no postexercise hyperemia occurred. Thus, in congestive heart failure, both the cutaneous and muscle beds of the forearm are abnormally constricted at rest, there is excessive vasoconstriction in both beds during leg exercise, and postexercise cutaneous vasodilation is abolished.