Changes of cardiac and respiratory rhythm in non- and tracheostomized rats exposed to nitrogen dioxide.

Cardiac and respiratory changes in non- and tracheostomized rats were examined during exposure to 20 ppm of NO2 for 150 min. The abnormal respiratory pattern consisted of rapid shallow breathing, deep breathing, and apnea, and the bradyarrhythmias were observed in the tracheostomized rats during exposure. Also, similar changes were seen in the nontracheostomized rats. A decrease in the heart rate (HR) was observed in both non- and tracheostomized rats. The decrease in HR was depressed by atropine injection, and the abnormal respiratory patterns were almost abolished by this drug. It was suggested, from these results, that the cardiac and respiratory abnormalities could be induced without the irritation to upper respiratory tracts, and that the vagal efferent pathway had an important role in the appearance of the abnormalities during exposure.