Chemodenervation does not alter cerebrovascular response to hypoxic hypoxia

We tested the hypothesis that sinoaortic chemodenervation would alter the increase in cerebral blood flow (CBF) during isocapnic hypoxic hypoxia in 1- to 7-day-old lambs. Lambs were anesthetized with pentobarbital and studied during moderate (arterial O₂ content [CaO₂] = 10 vol/100 ml) and severe (CaO₂ = 6 vol/100 ml) hypoxic hypoxia. Regional brain blood flows were measured with the radioactive microsphere technique. Cerebral oxygen consumption (CMRO₂) was calculated as the product of forebrain blood flow and the difference in oxygen contents between arterial and sagittal sinus blood. Lambs were then subjected to either sham surgery (n = 6) or to carotid chemodenervation and cervical vagotomy (n = 6). Chemodenervation was verified by abolition of the transient increase in blood pressure after intravenous injection of sodium cyanide in intact subjects. Neither sham surgery nor chemodenervation had an effect on CMRO₂ or CBF during hypoxic hypoxia. These data thus do not support the hypothesis that arterial chemoreceptors play any substantial role in the regulation of cerebral vascular tone during hypoxic hypoxia in the 1- to 7-day-old anesthetized lamb.