Correspondence of brain and rectal temperatures of guinea pigs in helium environments

Brain and rectal temperatures were measured in guinea pigs exposed to helium-oxygen environments at pressures as high as 50 bars. Very high correlations (r = .856, P less than 0.001) between the two values were observed, with an average difference of 0.47 degrees C (computed SD = 0.31). Brain temperature was usually higher than rectal. At a given ambient temperature, heat loss at 50 bars was more rapid than at 20 bars, which supports existing data for lower pressures. At 50 bars, normal equilibrium temperatures (approximately equal to 39 degrees C) could be maintained only if ambient temperature was in the vicinity of 35 degrees C. Lower ambient temperatures resulted in lower equilibrium temperatures. Between 33 and 39 degrees C, brain temperature can be predicted from rectal temperature, with an error of about 0.5 degree C.