Journal of Applied Physiology, Vol 62, Issue 2 421-428, Copyright © 1987 by American Physiological Society
Effect of habituation to subanesthetic N2 or N2O levels on pressure and anesthesia tolerance
R. W. Brauer, J. A. Dutcher, W. Hinson and W. S. Vorus
Exposure of CD-1 mice to subanesthetic partial pressures of N2O (0.5 atm)
or N2 (10-20 atm) for periods up to 14 days results in up to 40% decreases
in the mean threshold pressure eliciting type I high-pressure neurological
syndrome (HPNS) seizures, and in increases up to 38% in the N2 partial
pressure producing anesthesia. For all combinations of preexposure time, N2
partial pressure, as well as identity of the conditioning gas the relations
between the convulsion threshold pressure (Pc) and the anesthesia N2
pressure (Pa) appear to be uniquely correlated by the equation Pa = 54.5 -
0.2(Pc - 60)1.2. The potency of N2O with respect to these habituation
phenomena is between 28 and 33 times higher than that of N2, depending on
the aspects compared. Evidence is presented indicating that after 14 days
of habituation the animals have attained between 75 and 85% compensation
for the anesthetic as well as the anticonvulsant effects of the
conditioning gas. The bearing of the results on the problem of the nature
of the antagonism between inert gas narcotic agents and high pressure and
on the hypothesis that habituation tends toward restoration of isofluidity
(or some analogous normalization process) are discussed.
