Effect of hypothermia on the survival of the immature pig in a confined atmosphere.

The rat has an optimal body temperature (TB = 20 degrees C) for hypoxic survival in a confined space. The general applicability of this finding and the influence of body size was studied in immature pigs (27 kg). The pig consumed oxygen in a sealed chamber until it reached the terminal state. We measured blood pressure, inspired O2 and CO2, minute ventilation, ECG, ambient and body temperatures, and PO2, PCO2, O2-content and pH in arterial and venous blood. Four different cooling procedures produced a terminal TB of 26 +/- 3.1 degrees C, 30.1 +/- 2.9 degrees C, 30.0 +/- 2.8 degrees C and 22.6 +/- 2.1 degrees C and a terminal PIO2 of 28.0 +/- 10.2 torr, 30.8 +/- 7.6 torr, 31.5 +/- 5.6 torr and 41.7 +/- 15.4 torr respectively (mean +/- SD). Oxygen consumption, minute ventilation and cardiac output increased from baseline values of 0.5 l.h-1.kg-1, 10 l.min-1, and 6 l.min-1 respectively at the start of cold exposure, and declined moderately as a function of PIO2 below 60 torr. With respect to the relation between terminal body temperature and terminal PIO2 (but not PaO2), we found an optimal body temperature (26 degrees C) at which the animal can survive to the lowest PIO2. Using the allometric approach, i.e. linear extrapolation of temperature as a function of logarithm body mass, the optimal body temperature for man would be 27.5 degrees C. The advantage of hypothermia in the hypoxic survival of the whole animal is its effect on the reduction of the inspired-arterial O2 difference.