Exposure to heat: Comparison of responses of dog and man

In separate experiments dogs and men were exposed to various combinations of dry-bulb (DB) and wet-bulb (WB) temperatures (DB 37.8 to 54.4°C, WB 23.9 to 47.2°C). Rectal temperature (Tr), tolerance time (TT) and incidence of tetany were noted. In some experiments total plasma catecholamines and blood(venous or arterial) pH and\(P_{CO_2 } \) were also measured. Dogs were removed from the heat when Tr reached 42.0°C and men were removed when Tr reached 39.2°C or for other reasons.Dog and man, when exposed to particular environmental conditions, hyperventilate to the extent that, in man blood CO2 and pH approximate 20 mm Hg and 7.6 respectively and, in the dog 10 mm Hg and 7.7 respectively. When the heat load is very high,both dog and man hyperventilate earlier and the changes in blood pH and CO2 are more rapid. However, whereas man experiences intense carpopedal spasm, the dog does not, even though the changes in pH and CO2 are greater in the dog. There was no significant change in plasma catecholamines during heat stress.