Ventilatory recovery from hypothermia in anesthetized cats.

Ventilation and breathing pattern were recorded in a group of seven anesthetized cats during rewarming from 24 to 38 degrees C of esophageal temperature. It was found that at 24 degrees C, ventilation was very much depressed accounting for an alveolar hypoventilation resulting in hypoxia and hypercapnia. During rewarming, ventilation increased steadily; this was caused by sequential changes in central inspiratory activity (VT/Ti) and Ti/Tt ratio reflecting breath timing. Changes in VT/Ti have been initially attributed to an improvement in chemoresponsiveness and subsequently, to an involvement of supra-pontine thermoregulatory control areas during rewarming. Marked changes in breath timing, especially observed between 28 and 34 degrees C, have been attributed to a direct effect of rewarming upon the brain stem respiratory network. It has the result, that during hypothermia, several components of the respiratory control system are differently affected causing marked changes in breathing pattern and ventilation. They are accompanied by modifications in arterial blood pressure and heart rate.