Prediction of survival time of rats in severe heat

The response pattern of the rectal temperature of unanesthetized rats exposed to an acute heat in a room of 42.5 degrees C, rh 40% was analyzed in relation to survival time (S), equilibrium rectal temperature (Te), rise in Te from the initial temperature (Delta Te), and the slope of the changes in rectal temperature during the equilibrium period (Gt). A very wide fluctuation of the survival time (from 46.8 to 250.0 min) was observed between individual rats. For prediction of the survival time, following formula was obtained: log(S) = K1 - K2 times log (Te) - K3 times log (Delta Te) + k4 times 10- minus Gt. K1-4 are constants which differ according to sex. The predicted survival time showed highly constant results in individual rats when measured by repeated exposures. The predicted time coincided well with the survival time actually measured, the difference between the two (measured minus predicted) being 2.2 plus or minus 21.7 min (mean plus or minus SD) IN 77 RATS. There was also a significant correlation between the survival time predicted for acute heat exposure and the actual survival time of individual rats when they were exposed to a chronic heat by daily elevation of the rearing room temperature by 1.0 degrees C.