Role of the autonomic nervous system in the hypoxic response of the pulmonary vascular bed

The hypoxic pulmonary vascular response was evaluated in anesthetized dogs before and after bilateral cervical sympathectomy or vagotomy. A tracheal divider was used for independent ventilation of the right and left lungs. Relative distribution of perfusion to the right and left lungs was studied by the 133Xenon technique. Measurements were made with both lungs breathing room air and when one lung was ventilated on O 2 and the other on N 2 for varying times up to 30 min. Unilateral N 2 ventilation reduced perfusion by 33 %. The intensity of the response was inversely related to the Pa O 2 . Significant response occurred within one minute after the onset of hypoxia and maximal shift was reached by 10 min. Cervical vagotomy had no effect on the response. Perfusion to the hypoxic lung fell by 11 % after bilateral cervical sympathectomy suggesting the presence of two components to the hypoxic pulmonary vascular response, one occurring locally and one reflexly mediated through the sympathetic system.