Arterial blood gas status in rats exposed to chronic CO at low and high altitude.

Arterial blood gases were measured in 52 unanesthetized Sprague-Dawley rats following six weeks exposure to either room air at ambient altitude (950 m), room air containing 100 ppm CO at ambient altitude, room air at 4575 m simulated high altitude, or room air containing 100 ppm CO at 4575 m simulated high altitude. PaCO2 was significantly higher in animals exposed to CO both at ambient altitude (38.2 vs 34.5 Torr) and simulated high altitude (28.3 vs 23.6 Torr). The data show that chronic exposure to low concentrations of CO depresses ventilatory drive at both ambient and simulated high altitude. This depression could be related to changes in brain blood flow and the acidity of the central medullary chemosensitive area or to changes in peripheral chemoreceptor activity.