Habituation of thermal sensations, skin temperatures, and norepinephrine in men exposed to cold air

We studied habituation processes by exposing six healthy men to cold air (2 h in a 10 degreesC room) daily for 11 days. During the repeated cold expos ures, the general cold sensations and those of hand and foot became habitua ted so that they were already significantly less intense after the first ex posure and remained habituated to the end of the experiment. The decreases in skin temperatures and increases in systolic blood pressure became habitu ated after four to six exposures, but their habituations occurred only at a few time points during the 120-min cold exposure and vanished by the end o f the exposures. Serum thyroid-stimulating hormone, total thyroxine and tri iodothyronine, norepinephrine, epinephrine, cortisol, and total proteins we re measured before and after the 120-min cold exposure on days 0, 5, and 10 . The increase in norepinephrine response became reduced on days 5 and 10 a nd that of proteins on day 10, suggesting that the sympathetic nervous syst em became habituated and hemoconcentration became attenuated. Thus repeated cold-air exposures lead to habituations of cold sensation and norepinephri ne response and to attenuation of hemoconcentration, which provide certain benefits to those humans who have to stay and work in cold environments.