Peripheral vascular responses to hypoxic hypoxia after aortic denervation

We wished to see whether aortic chemoreceptors and other vagal afferent traffic played an essential role in the circulatory adjustments to hypoxic hypoxia. Aortic chemoreceptors were denervated (AD) in one group (n = 6) of anesthetized dogs, bilateral cervical vagotomy (V) was done on a second group (n = 6), and a third group (n = 6) was sham-operated to serve as a control. Venous outflow from the left hindlimb was isolated. After a 20-min control period of ventilation with room air, the animals were ventilated for 60 min with 9% of O2 in N2. Arterial, mixed venous, and hindlimb venous blood samples were taken every 20 min. The cardiac output response to hypoxic hypoxia was attenuated at 40 and 60 min in both the AD and V groups (p less than 0.05). Hindlimb blood flow increased equally in all three groups during hypoxia. The pressor response at the onset of hypoxia (20 min) was abolished in the AD and V groups, but mean arterial pressure fell to similar levels in all three groups by 60 min of hypoxia. We concluded that reflex aortic chemoreceptor stimulation during hypoxia augmented cardiac output mostly by effects on the venous side of the circulation but played no role in skeletal muscle vascular responses to hypoxic hypoxia.