Nose-Only Exposure of Rats to Carbon Monoxide

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Abstract
Animals were exposed nose-only to 0, 527, 1091, or 1800 parts per million (ppm) carbon monoxide for 1 h/day, for 74 consecutive days. Blood carboxyhemoglobin (COHb) concentrations in the 1800 ppm group approached those concentrations associated with lethality (62+%). Respiratory minute volume was reduced to 73% of preexposure values in animals exposed to 1800 ppm CO, through changes in respiratory rate. Most of the erythrocyte parameters showed increases that were proportional to the CO concentration. Accumulation half-lives for COHb in the low, medium, and high exposure groups were 17.2, 12.6, and 9.0 min, respectively; the elimination half-lives were 42.3, 32.6, and 29.7 min, respectively Heart weights were increased by up to 32% in males and 47% in females as a result of this very high exposure to 1800 ppm CO. Chronic inflammation was observed in the cardiac muscle of animals exposed to 1800 ppm CO. The inflammation consisted of scattered interstitial aggregates of lymphohistiocytic cells, found most frequently in the ventricular walls and septum. In a few instances, the inflammatory infiltrations were accompanied by minimal amounts of muscle-fiber atrophy and necrosis.