Temperature regulation in the dog in helium-oxygen environments

Helium-oxygen mixtures have been reported to alter thermoregulation in humans and animals because of convective heat transfer differences between a helium-oxygen and a nitrogen-oxygen environment. Thermoregulation in unrestrained dogs was tested in a chamber at temperatures of 23, 33, and 43 degrees C, in air or 80% helium-20% oxygen (HeO). Respirations in air in these temperatures were 15, 134, and 322 breaths/min, respectively. Heart rates increased with chamber temperature, averaging 69 at 23, 82 at 33, and 103 beats/min at 43 degrees C. In HeO, responses to increasing temperatures differed from air. Respiration was 13 at 23, 49 at 33, and 336 breaths/min at 43 degrees C. Heart rates were 79 at 23, 70 at 33, and 97 at 43 degrees C. Rectal temperatures rose in both atmospheres at 43 degrees C. Shivering occurred in dogs in HeO at 23 degrees C but not in air. Results indicated that the dogs' thermoregulatory responses were markedly different in the two gas mixtures due to convective heat transfer differences, which were especially noticeable when responses in HeO at 33 degrees C were compared to those in air.