Nocturnal temperature and subcutaneous blood flow in humans

The aim of this study was to investigate the possible relationship between variations in local skin and body temperatures, and a subcutaneous hyperaemia response during sleep in humans. Nocturnal subcutaneous blood flow (SBF) was measured in the lower legs of 9 subjects for 8-12 h under outpatient conditions. The core temperature was measured by a tympanic membrane temperature sensor, and the local skin temperature was measured by a skin temperature sensor. The 133Xe wash-out technique with portable CdTe(Cl) detectors was used for measurement of the SBF. The SBF increased significantly (P < 0.0001) after 1 h sleep, with the hyperaemia persisting for 2 h. During the hyperaemic phase, the local skin temperature increased significantly (P < 0.0001) and then decreased again in the post-hyperaemic phase (P < 0.01). The core temperature decreased significantly during the measurement period (P < 0.01). Separate ordinary linear regression analyses revealed no significant correlations between the measured temperature parameters and the blood flow levels during sleep. The results indicate no governing role of the local skin or body temperatures on the local SBF. The local skin temperature increased significantly secondary to the nocturnal subcutaneous hyperaemia (i.e. active vasodilatation), which is believed to be involved in a thermoregulatory effector mechanism.