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To find whether exercise or upright posture affected the internal temperature threshold for cutaneous vasodilation or the relationship between skin blood flow (SkBF) and sweat rate (SR), the relationship of esophageal temperature (Tes) to forearm SkBF and SR was measured in four settings: supine rest, upright rest, supine exercise, and upright exercise. All studies were performed at an elevated skin temperature (38-38.5 degrees C). Compared with values from supine rest, upright exercise was associated with an increase in the internal temperature threshold for vasodilation of 0.39 +/- 0.07 degrees C (P less than 0.01), whereas there was no significant alteration in the threshold for the onset of sweating. Neither the ultimate slope of the SkBF-Tes relationship nor that of the SR-Tes relationship was altered by upright exercise. The upright posture and exercise each contributed to the elevation in the threshold for cutaneous vasodilation, with the average shifts being 0.11 +/- 0.05 degrees C (P less than 0.05) and 0.28 +/- 0.08 degrees C (P less than 0.01), respectively. The net effect of this shift in threshold was to reduce the level of SkBF at any level of Tes during exercise and to increase the difference in threshold between vasomotor and sudomotor responses.
Johnson et al. (Wed,) studied this question.