Control of Skin Blood Flow at the Boundaries of the Thermal Comfort Zone

Abstract

PURPOSE: The control of skin blood flow in the thermal comfort zone is largely unknown. We tested the hypothesis that skin blood flow at the boundaries of the thermal comfort zone is predominantly under reflex control. METHODS: Ten healthy subjects (age: 26 ± 4 y, 4 females) wearing shorts and a t-shirt underwent a 90 min behavioral test in which they voluntarily moved between a warm (39.9 ± 0.2°C, RH: 20 ± 0%) and a cool (16.9 ± 1.4°C. RH: 49 ± 3%) room when they felt ‘too warm’ or ‘too cool’. This test defined the boundaries of the thermal comfort zone for each subject. Skin blood flow was measured continually on the ventral forearm at two locations using laser Doppler flowmetry. One of these locations was maintained at 34°C, ensuring skin blood flow was under reflex control (RFX). The temperature of the other location was not controlled, and thus, skin blood flow was under local and reflex control (L+RFX). Blood pressure (Finometer), and weighted mean skin and rectal temperatures were also measured continually. Data are reported as a 30 s average immediately prior to moving from cool to warm (C→W) or warm to cool (W→C). Data were averaged across behaviors for a given subject (behaviors/subject = 9 ± 3). Skin blood flow data are reported as absolute values, the change from pre-test baseline, and as cutaneous vascular conductance (CVC). RESULTS: Mean skin temperature was different at C→W (33.5 ± 0.7°C) compared to W→C (36.1 ± 0.5°C, P<0.01), but rectal temperature did not differ at these points (C→W: 36.8 ± 0.2°C, W→C, 36.7 ± 0.2°C, P=0.17). At baseline, C→W and W→C, absolute skin blood flow and CVC were higher at RFX compared to L+RFX (P≤0.01). However, at both locations absolute skin blood flow and CVC were higher (P<0.01) at W→C compared to C→W (P<0.01), which was also consistent with the change from baseline data (P<0.01). Nevertheless, whether expressed as skin blood flow or CVC, the change from baseline at RFX compared to L+RFX was not different at either W→C (RFX: +21 ± 23 PU, +0.27 ± 0.24 mmHg/PU vs. L+RFX: +29 ± 15 PU, +0.33 ± 0.16 mmHg/PU; P≥0.10) or C→W (RFX: -6 ± 15 PU, -0.09 ± 0.16 mmHg/PU vs. L+RFX: -3 ± 6 PU, -0.04 ± 0.06 mmHg/PU; P≥0.39) CONCLUSION: These data indicate that changes in skin blood flow at the boundaries of the thermal comfort zone are largely under reflex control in young healthy adults.