The cerebral vasculature is exquisitely sensitive to changes in leadtshteopcaerrteibalraplrvesassuordeiloafticoanrbaonnddhiyopxeidrpee(rPfCusOio2)n. Hypercapnia and, recipro- cally, hypocapnia is a potent mediator of cerebral vasoconstric- tion leading to decreased cerebral blood flow (1). ...