If the patients survives the acute episode, elimination of carbon monoxide occurs in the rate of a halt-time of 3 to 4 hours. Nevertheless, there may remain after effect. Therefore, the present study was desinged to elucidate the change of myocardial tissue caused by acute carbon monoxide poisoning were evaluated by electrton microscopic observation of the severity of the mitochondrial swelling and cytochrome oxidase activity, which was demonstrated by histochemical staining with diaminobenzidine(DAB).

Male Sprague-Dawley rats were exposed to the carbon monoxide of 1500 ppm for 150 minutes. They were divided into two groups ; one group were treated with hyperbaric oxygenation 15 minutes after carbon monoxide exposure, the other were not treated. Rats were sacrified 6 hours, 12 hours, 1 day, 3 days, 7days, 14 days, and 21 days after carbon monoxide exposure. The specimens were collected from the apex of the heart.

In the group without hyperbaric oxygenation, mitochondrial swelling subsided 21 days after carbon monoxide exposure accompained by restoration of cytochrome oxidase activity. On the other hand, with hyperbaric oxygenation, healing process was shortened. Cytochrome oxidase activity was restored 7 days after carbon monoxide exposure.