Chronic exposure to carbon monoxide at high altitude: effects on mean electrical axis.

The effects of breathing CO continuously at high altitude on the mean electrical axis of the heart, hematocrit ratio and body weight were studied in laboratory rats. Laboratory rats were exposed for 6 weeks to: 100 or 500 ppm CO; 15,000 feet stimulated high altitude (SHA); or 100 or 500 ppm CO at SHA. SHA decreased body weight significantly; CO and CO-SHA interaction had no significant effect on body weight. CO and SHA increased hematocrit ratio significantly; five hundred ppm CO increased hematocrit ratio to a greater extent than 100 ppm CO. There was a significant interaction between 500 ppm CO and SHA on hematocrit ratio. The mean electrical axis (MEA) was shifted to the right by SHA, and shifted to the left by CO. The effect was dose dependent, with the greater left shift occurring with 500 ppm CO. There was a significant interaction between 500 ppm CO and SHA on the MEA. These results indicate that, in general, the effects produced by 15,000 feet SHA are not intensified by 100 ppm CO, but are intensified by 500 ppm CO.