RESPONSES OF THE VEINS AND ARTERIOLES OF THE FOREARM TO WALKING DURING ACCLIMATIZATION TO HEAT IN MAN *

Abstract

Plethysmographic studies of venous tone and blood flow of the forearm were carried out to determine whether or not the increasing adequacy of general circulation with acclimatization to heat was associated with alterations of peripheral circulation. Subjects were acclimatized to heat by walking for 30 minutes 4 times a day on a treadmill at 3.5 mph with a 5% grade. Two studies of 4 subjects each were carried out with 2 and 1 control days respectively (77[degree]F), and in 9 and 6 heat days (120[degree]F) respectively. The veins of the forearm constricted in response to walking in both environments. This veno-constriction on days 3 and 4 in the hot environment was significantly greater than that of other days in the heat or in the control environments. Blood flow of the forearm during walking was much greater in the hot environment than in the cool environment but relatively less on days 3 and 4 in the hot environment than on other days in the hot environment. Peripheral vascular responses to walking in the heat were most intense on days 3 and 4 in the hot environment when the men showed the greatest subjective improvement with walking in the heat. These effects did not persist, however, suggesting that other factors also contributed to the improved circulatory responses with acclimatization to heat.