A simple gradient calorimeter was developed for measurements of nonevaporative heat loss of the head, and used on three subjects, with heads unprotected but the body adequately clothed, at temperatures between 32°C and − 21°C. Heat loss was linearly related to external temperature by the regression equation (correlation coefficient 0.97 ± 0.01), H = (284.8 – 7.55 x t°C) in K Cal/m2 of head per hour. This means that at −4°C the heat loss from the head may amount to half the total resting heat production of the man. The insulation of the tissues of the head was calculated as about 0.4 clo units, and did not change with the external temperature. To see if it would change if there was general vasoconstriction or vasodilation, a second series of experiments was carried out: a) at 10°C with the subjects unclothed; b) at 20°C with the subjects clothed; and c) at 29°C with subjects clothed and with a heating pad on the chest. While the tissue insulation of the finger increased by a factor of six times in (a) compared with (b), that of the head was constant. In (c) the tissue insulation of the head decreased slightly, indicating slight vasodilation. The importance of insulation of the head in the cold to extend the tolerance time is pointed out by practical examples.
Submitted on October 17, 1956
- Copyright © 1957 the American Physiological Society