Ventilation of lungs in deeply hypothermic rats

Abstract

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. Submitted on October 26, 1960