Heart rate and core temperature as indicators of heat stress during deep underwater activity.

In hyperbaric environments, comfortable ambient temperatures are necessarily higher than normal room temperature, and high levels of humidity are also common. These conditions are stressful and even hazardous for an exercising diver. We monitored the heart rates and core temperatures of divers participating in deep experimental dives to pressures up to 300 msw. Accelerated heart rates (100 to 180 beats/min) and elevated core temperatures (+0.4 to 0.9 degrees C) were registered. The increase in heart rate can be explained by the rise in core temperature. Formulas are presented for the relationships between heart rate and duration of activity, between core temperature and duration of activity, and between heart rate and core temperature. These formulas allow the estimation of core temperature from the diver's pulse, and serve to prevent excessive heat stress which could lead to an accident.