Effect of sympathetic nervous system stimulation on cerebrovascular CO2 responsiveness

Cerebrovascular CO2 responsiveness, following noradrenaline (NA) infusion, was studied in the cat by continuous measurement of cerebral tissue oxygen tension (BrPO2), carbon dioxide tension (BrPCO2), pH (BrpH), and blood pressure (BP). Intravenous infusion of NA (1 microgram/kg/min) was done to stimulate the adrenergic nervous system. Inhalation of 5% CO2+air was performed for 3 minutes before, during, and after NA infusion. Cerebrovascular CO2 responsiveness was estimated from changes in BrPO2, BrPCO2, and BrpH. CO2 inhalation increased BrPO2, BrPCO2, and BP, but decreased BrpH, in the respective 3 stages. delta BrPO2 decreased significantly during NA infusion, but recovered after cessation of NA. NA infusion caused a decrease in CO2 responsiveness. This suggests that sympathetic hyperactivity can modify cerebrovascular CO2 responsiveness.