Abstract
Bradycardiac response to nonapneic facial immersion in man was examined at water temperatures of 10, 20, 30, 35, 40, and 47°C. The response was mainly dependent on the water temperature. In general, the colder the water, the greater the response. However, the least response was noted at 40°C; at 47°C the bradycardia was greater than at 40°C. The bradycardiac response was generally more marked in trained swimmers and divers than in subjects unaccustomed to swimming. The magnitude of changes in facial skin temperature appeared to have an additional influence on the cardiac slowing. Heart rate reached the minimum value in 20-30 sec, then tended to return toward the initial rate during immersion. Stimulation of cutaneous cold receptors is assumed to be most responsible for the development of bradycardia on nonapneic facial immersion, and the return of heart rate during immersion may be attributed to adaptation of these receptors.
