Graded cutaneous vascular responses to dynamic leg exercise

The cutaneous vascular conductance-esophageal temperature (CVC-Tes) relationship was examined at five work loads (75-200 W) in each of four men to find whether there is a role for exercise intensity in the control of skin blood flow (SkBF). Several factors contributed to our evaluation of the CVC-Tes relationship during work. Laser-Doppler velocimetry (LDF) provided a continuous measure of SkBF that is not influenced by underlying muscle blood flow. Local warming to 39 degrees C at the site of measurement of SkBF provided a consistent skin temperature and facilitated observation of changes in LDF. Mean arterial pressure was measured noninvasively once per minute to calculate CVC. Supine exercise minimized baroreceptor-induced cutaneous vasoconstriction. Our major finding was that the internal temperature at which CVC began to rise during exercise (CVC threshold) was graded with work load beyond 125 W (P less than 0.05). In that range the CVC threshold increased by 0.16 degrees C for every increment of 25 W. The CVC threshold was never reached at the highest work load in three of the four subjects. There was no consistent effect of work load on the slope of the CVC-Tes relationship or on the internal temperature at which sweating began during exercise (sweat rate threshold). We conclude that the level of work beyond 125 W affects the CVC-Tes relationship in a graded fashion, principally through shifts in threshold.