Influence of vagal blockade on respiratory and circulatory functions in hypothermic dogs

¹ Department of Physiology and Pharmacology, Duke University Medical Center, Durham, North Carolina

Anatomical and physiological dead spaces were enlarged as a result of reduction in body temperature to 28 C in spontaneously respiring anesthetized dogs. Respiratory dead space at 32 C was not significantly different from that at normal body temperature. Vagal blockade resulted in an increase in tidal volume and decrease in respiratory frequency and increased anatomic and physiologic dead space at normal and reduced temperatures. Alveolar ventilation and cardiac output declined equally (percentagewise) with reduction in body temperature to 32 C; at 28 C alveolar ventilation fell more precipitously so that alveolar ventilation-cardiac output ratio (ventilation-perfusion) at 28 C was approximately one-half that at 37 and 32 C. Arterial-alveolar carbon dioxide pressure differences were independent of temperature and vagal blockade. The results indicate no impairment of gas transport or gas exchange at 32 or 28 C in spontaneously respiring anesthetized dogs.