Human Cardiovascular Adjustments to Rapid Changes in Skin Temperature during Exercise

Abstract

In 11 normal men, central circulatory responses were measured while skin temperature was changed in a square-wave pattern during uninterrupted exercise (26% to 64% maximal oxygen consumption). Skin temperature was changed at 30-minute intervals, beginning at 32°C. On raising it to 38.2°C at low oxygen consumption (Vo 2 ), cardiac output increased 2.5 liters/min, and central blood volume, aortic mean pressure, and stroke volume fell (7%, 7%, and 11%, respectively). Right atrial mean pressure fell 2.2 and 2.3 mm Hg during control and heating periods, respectively. All variables returned to control levels when skin temperature was reduced toward 26.9°C. Raising it to 40°C reproduced these changes with a more clear-cut drop in right atrial mean pressure. Results indicated reduced peripheral venous tone and cutaneous pooling of blood during heating and rapid reversal on cooling. On raising skin temperature to 38.7°C at high Vo 2 , cardiac output increased 19% (3.1 liters/min), stroke volume decreased 14%, and central blood volume rose slightly. Aortic mean pressure fell during the control period and was maintained or rose during heating periods. On cooling, central blood volume and stroke volume rose, cardiac output remained elevated, and aortic mean pressure fell. Increases in cardiac output during heating were related to skin temperature and not to Vo 2 or body temperature. At high Vo 2 , circulatory adjustments favor metabolic rather than thermoregulatory demands. This work was supported in part by U. S. Public Health Service Grant HE-09773 from the National Heart Institute. A part of this study was conducted through the Clinical Research facility of the University of Washington, supported by the National Institutes of Health (Grant FR-37). ADDITIONALDr. Rowell was an Established Investigator of the American Heart Association and was supported by the Washington State Heart Association.A preliminary report of this work was presented at the annual meeting of the American Heart Association, November 23, 1968, Miami, Florida. Received August 19, 1968. Accepted for publication March 25, 1969. thermal and metabolic stresses have depended upon manipulation of environmental temperature rather than skin temperature. But, where natural conditions are simulated, skin temperature may vary throughout the exposure (1). It will also vary over the body surface and may well be reduced, the more severe the exercise, due to an increased sweating response (1). In short, skin temperature is not tightly controlled by exposing subjects to controlled environments, but it is important in both direct local control and reflex control of the vasoactive state of the skin (2). Accordingly, it is important to control this variable when attempting to understand the mechanisms governing human cardiovascular responses to metabolic and thermal stresses. Our experimental design was based on controlling skin temperature as closely as possible and manipulating it in a square-wave pattern between extremes during uninterrupted exercise. It ...

Hypohydration impairs endurance exercise performance in temperate but not cold air

“…It therefore remains possible that cold skin in cold HYP (Fig. 3B) maintained a larger central blood volume and better preserved stroke volume and cardiac output (9,17,19,22,29). Similar T re and HR at exhaustion between cold HYP and temperate HYP also seem to support this conclusion since performance in temperate HYP, but not cold HYP, was less than cold and temperate EUH ( Table 1).…”

Circulatory and thermal responses of men with different training status to prolonged physical work in dry and humid heat.

“…On the other hand, the increases in cardiac output were significantly related to increases in skin blood flow, as estimated by the thermal conductance. Similarly, a significant correlation (0.74) between increases in cardiac output and skin temperature was found during light exercise in water-perfused suits, in which the skin temperature was maintained at different levels (30). Thus at lower work loads higher thermal stress, as indicated by skin temperature or skin blood flow, may be coupled with elevated cardiac output, despite reduced stroke volume.…”

“…The mechanism behind the reduced stroke volume in the heat seems to be related to the increased level of skin blood flow (30), which, together with the reduction in the tone of distensible cutaneous veins (35), increases the pressure and blood volume of the veins. Because 70 % of the blood volume is below heart level in humans and most of it is in the veins, the venous pooling of blood under heat stress reduces cardiac filling, central blood volume, and stroke volume (30). In an upright walking man the muscle pump empties the veins during each contraction, but the arterial inflow is so high that the average venous pressure and volume are increased (10).…”

Pooling in Chronic Orthostatic Intolerance

“…28 Venoconstriction to adrenergic stimulation is regional; thus, there is excellent evidence dating to Donegan's work 29 on human splanchnic and cutaneous venoconstriction in response to sympathetic stimulation, but there is less evidence for the response of other venous beds. Cutaneous nerves mainly subserve thermal reflexes 30 and not the arterial baroreflex, and even the splanchnic response depends on passive redistribution. 31 The idea of a uniform generalized sympathetic/autonomic response to maintain homeostasis 32 has not been demonstrated in practice.…”