Cold acclimatization and finger numbness.

Abstract

Evidence is scarce on the alterations in human performance that follow repeated exposure to cold climates. These experiments have therefore attempted to establish whether people show any measurable changes in hand function when they live in cold environments. The investigations started as field studies in Canada and continued as cold-room researches later in England. The field tests in the sub-Arctic were mostly in terms of tactile sensitivity of the fingers. The volunteers for these tests were termed either indoor or outdoor men, according to the amount of time they usually worked outside. Their fingers were chilled for 6 min, and it was found that air temperatures of — 16 to — 25° C at wind speeds of about 4 m.p.h. had a much greater numbing effect on the indoor men. One criterion used for numbness estimation was the two-point tactile discrimination threshold. The increase in this threshold was seven times greater for the indoor men, although both groups had equally sensitive fingers before cold exposure. A definite but smaller difference was also found after exposure as regards their vibration-detection thresholds. Over a large range of wind-chill conditions the indoor men gave a marked and linear increase in their two-point thresholds. But with the same changes in environmental severity the outdoor men showed no such alteration in sensitivity. Extremely severe exposures, however, did give equally marked numbness in both groups. The higher the skin temperatures after exposure, the less were the numbness scores in either group. [Other workers have shown that Eskimos have higher skin temperatures and resting hand blood flows than white men (Brown & Page 1952).] The outdoor men had higher finger-skin temperatures before and particularly after the experimental cold exposures. Possibly, then, the outdoor men might have developed a greater resting finger blood flow which more effectively maintained their finger warmth and tactile discrimination. This suggestion needs study by further cold-room research. Cold-room experiments have shown so far that short daily exposures have a cumulative effect during the winter-time; the increase in the two-point threshold after chilling was halved within 2 to 5 weeks. But an English summer prevented this adaptation taking place. Would either recent tropical experience or concurrent hot-room exposure also hinder acclimatization to cold?