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Our purpose if to develop a survival strategy for man trapped in a confined space. A previous study showed that in the rat there is a critical exposure time beyond which hypoxic survival improves. To evaluate the general applicability of these findings in the rat and the influence of body size, the effect of exposure time on hypoxic survival was studied in immature pigs (26 kg). The pig consumed the oxygen in a sealed chamber until hypoxic collapse. We measured blood pressure, oxygen consumption, inspired O2 and CO2, minute ventilation, ECG, body temperature, and PO2, PCO2 and pH in arterial and venous blood. Five groups of pigs were confined in different initial volumes of air, producing total exposure times of 0.5, 1.3, 2.3, 4.8 and 6.7 h. There was no significant difference between the experimental groups for any of the parameters measured during the exposure. Unlike the rat, in the pig there was no "adjustment time" beyond which the animal could survive to a lower PIO2. Terminal inspired PO2 increased as a function of exposure time. This was related to either hypoventilation or lung edema. There was a correlation between the level of carbon dioxide in the blood at 60-70 torr inspired oxygen and the terminal PO2. Pigs which failed to clear the carbon dioxide succumbed early to hypoxia. In a confined space it is preferable to maintain normoxic conditions for as long as possible.

Effect of Exposure Time on the Survival of Immature Pigs in a Confined Atmosphere