Respiratory and other responses in subjects immersed in cold water.

Subjects have been immersed in water at 27 degrees C and 10 degrees C and while immersed their respiratory rates, minute volumes, and end-tidal PCO2 levels were measured. Measurements were made with the subjects at rest, exercising at approximately 0.8 liter oxygen-min-1, and very vigorously at 1.8-2.0 liters oxygen-min-1. Immersion in the cold water caused an increase in respiratory rate and a fall in end-tidal PCO2. At the moderate rate of exercise the hyperventilation persisted in relation to the oxygen demand and there was still a significant reduction in end-tidal PCO2. At the greatest rates of exercise, the end-tidal PCO2 did not differ from that obtained in similar rates of exercise in warm water. Preheating the subject in a sauna so as to increase skin temperature, with minimal change in body temperature, greatly attenuated the ventilatory and end-tidal PCO2 responses to cold water immersion. The significance of these findings is discussed.