Ventilation of lungs in deeply hypothermic rats

¹ Department of Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York

Ventilation (Vi), oxygen consumption (Vo₂) and heart rate (H) were measured at esophageal temperatures (T) of 8–24 C. The trachea was cannulated; a body plethysmograph and pressure transducer registered breath volumes. Vo₂ was computed from oxygen content of effluent air. Vi, Vo₂, and H were each related to T by a regression of low slope from 8 to 18 C, and a high nearly-linear slope above 18° But the proportions among the three parameters changed; Vi was relatively less below 18°. Breaths were increasingly irregular as T decreased below 24°. Hypoxia induced greater Vi at 16–21°, but not at 13°, nor after excision of the carotid bodies. Vo₂ in hypoxia was greatly reduced; at 12–17° a Vo₂ as low as one-fifth of that in air continued for an hour. H also decreased sharply at Po₂ below 50 mm Hg. Carbon dioxide induced faster Vi even at 12°; its effects were not modified by carotidectomy. Gasps were regularly induced by hypoxia, and usually by hypercapnia; they occurred just as frequently after carotidectomy.