Using skin temperature gradients or skin heat flux measurements to determine thresholds of vasoconstriction and vasodilatation

Forearm-fingertip skin temperature differentials (Tsk-diff) are used to indicate vasomotor tone, vasoconstriction defined as having occurred when Tsk-diff greater than or equal to4degreesC (Sessler et al. 1987, 1988a, b). This study was conducted to determine whether Tsk-diff or finger pad heat flux (HF) can be used to predict when vasoconstriction and vasodilatation occur. Seven subjects (one female) sat in water at [mean (SD)] 40.7 (0.8)degreesC until their core temperature (T,) increased by 1degreesC, ensuring vasodilatation. The water was then cooled [at a rate of 0.6 (0.1)degreesC.min(-1)] until T-c fell to 0.5degreesC below pretesting values, causing vasoconstriction. Subjects were then rewarmed in water [41.2 (1.0)degreesC]. Skin blood flow (SkBF) was measured using laser Doppler flowmetry (LDF) on the left second finger pad [immersed in water at 10.4 (1.4)degreesC as part of another experiment], and infrared plethysmography on the third finger pad of both hands. Tsk-diff and HF were measured on the right upper limb, which remained in air. When vasodilated, the subjects had a stable Tsk-diff and HE During cooling, rapid-onset vasoconstriction occurred coincidental with large gradient changes in HF and Tsk-diff (inflection points). In two subjects the original vasoconstriction definition (Tsk-diff greater than or equal to4degreesC) was not attained, in the other five this was achieved 31-51 min after vasoconstriction. During rewarming, the Tsk-diff and HF inflection points less accurately reflected the onset of vasodilatation, although with one exception they were within 5 min of the LDF changes. We conclude that Tsk-diff and HF inflection points predict vasoconstriction accurately, and better than Tsk-diff greater than or equal to4degreesC.