Independence of hypoxic death of inspiratory PCO2 in rats and fossorial mole rats.

Laboratory white rats and fossorial mole rats (Spalax ehrenbergi) were subjected to progressive hypoxia by enclosure in a thermoregulated, confined atmosphere. Variable levels of environmental CO2 were obtained by controlling the duration of CO2 absorbance. Rats had preimplanted electroencephalographic (EEG) and electrocardiographic (EKG) electrodes and a rectal temperature probe. Animals were followed until their last gasp and EEG flattening, at which time the chamber's atmosphere was analyzed. The mole rat demonstrated a significantly lower terminal PIO2 [20.9 +/- 3.5 (SD) vs. 38.0 +/- 8.4 (SD) Torr]; however, in both animals terminal PIO2 was independent of PICO2 over a range of the latter of 0-117 Torr. Rats showed a progressive decline in rectal temperature from a PIO2 of 80 Torr on, amounting finally to 2.3 degrees C. The rats' oxygen consumption was maintained down to a PIO2 of 65 Torr and declined from then on. A group of rats with maximal CO2 accumulation showed a greater decline of rectal temperature and a steeper drop of VO2 with respect to PO2 compared to a group with no CO2 buildup. The main result was unexpected, in view of the theoretical synergism of the adverse effects of hypoxia and hypercapnia, and should reorient current thinking on survival and resuscitation in confined spaces.