Hypoxia increases the cutaneous threshold for the sensation of cold

Cutaneous temperature sensitivity was tested in 13 male subjects prior to, during and after they breathed either a hypocapnic hypoxic (HH), or a normocapnic hypoxic (NH) breathing mixture containing 10% oxygen in nitrogen. Normocapnia was maintained by adding carbon dioxide to the inspired gas mixture. Cutaneous thresholds for thermal sensation were determined by a thermosensitivity testing device positioned on the plantar side of the first two toes on one leg. Heart rate, haemoglobin saturation, skin temperature at four sites (arm, chest, thigh, calf) and adapting temperature of the skin (Tad; degrees centigrade), i.e. the temperature of the toe skin preceding a thermosensitivity test, were measured at minute intervals. Tympanic temperature (Tty; degrees centigrade) was measured prior to the initial normoxic thermosensitivity test, during the hypoxic exposure and after the completion of the final normoxic thermosensitivity test. End-tidal carbon dioxide fraction and minute inspiratory volume were measured continuously during the hypoxic exposure. Ambient temperature, Tty, Tad and mean skin temperature remained similar in both experimental conditions. Cutaneous sensitivity to cold decreased during both HH (P