Skin-temperature perturbation experiment

Twelve resting volunteers wore a water-perfused suit. Tubes covered the torso, upper arms and legs; the right forearm remained uncovered for laser Doppler blood-flow measurement. Six thermocouples estimated mean skin temperature; a sublingual thermocouple measured oral temperature. A dry-air capsule measured local sweat output from outgoing air moisture. ^[ref]

After two control scans near $34{}^{\circ }\mathrm{C}$ skin temperature, the suit cooled and then warmed the skin. Mean oral temperature was $36.6{}^{\circ }\mathrm{C}$ during both cooling and early warming; mean skin readings were $30.5$ and $38.2{}^{\circ }\mathrm{C}$. Cutaneous vascular conductance fell during cooling and rose during warming. The inference is that compensatory blood-flow responses can precede an appreciable internal temperature change. ^[ref]

Repeated baselines controlled comparison within participants; closed mouths reduced oral-probe cooling artifacts. A later control with reduced oral temperature was excluded. Oral temperature is a proxy, local flow is not whole-body heat transfer, and the fixed condition order leaves time effects possible. Brain imaging measured regional blood flow, not direct neuron firing or causal necessity. ^[ref]