HUMAN TEMPERATURE REGULATION DURING NARCOSIS INDUCED BY INHALATION OF 30-PERCENT NITROUS-OXIDE

The study investigated the effect of inhalation of 30% nitrous oxide (N2O) on temperature regulation in humans. Seven male subjects were immersed to the neck in 28-degrees-C water on two separate occasions. They exercised at a rate equivalent to 50% of their maximum work rate on an underwater cycle ergometer for 20 min and remained immersed for an additional 100 min after the exercise. In one trial (AIR) the subjects inspired compressed air, and in the other trial (N2O) they inspired a gas mixture containing N2O (20.93% O2-30% N2O-49.07% N2). Sweating, measured at the forehead, and shivering thermogenesis, as reflected by O2 uptake, were monitored throughout the 100-min recovery period. The threshold core temperatures at which sweating was extinguished and shivering was initiated were established relative to resting preexercise levels. Neither the magnitude of the sweating response nor the core threshold at which it was extinguished was significantly affected by the inhalation of N2O. In contrast, shivering thermogenesis was both significantly reduced during the N2O condition and initiated at significantly lower core temperatures [change in esophageal temperature (DELTAT(es)) = -0.98 +/- 0.33-degrees-C and change in rectal temperature (DELTAT(re)) = -1.26-degrees-C] during the N2O than during the AIR condition (DELTAT(es)) = -0.36 +/- 0.31-degrees-C and DELTAT(re) = -0.44 +/-0.22-degrees-C). The null zone, defined. as the range of core temperatures between the-thresholds for cessation of sweating and onset of shivering, was significantly enlarged from 0.59 +/- 0.27 and 0.59 +/- 0.16-degrees-C, as determined with T(es) and T(re) in the AIR condition, to 0.95 +/- 0.50 and 1.32 +/- 0.38-degrees-C in the N2O condition, respectively.