Effect of hyperoxia, hypercapnia, and hypoxia on cerebral interstitial oxygen tension and cerebral blood flow

The assessment of cerebral interstitial oxygen tension (piO₂) can provide valuable information regarding cerebrovascular physiology and brain function. Compartment-specific cerebral piO₂ was measured by ¹⁹F NMR following the infusion of an oxygen-sensitive perfluorocarbon directly into the interstitial and ventricular space of the in vivo rat brain. ¹⁹F T₁ measurements were made and cerebral piO₂ were obtained through in vitro calibrations. The effects of graded hyperoxia, hypercapnia, and hypoxia on piO₂ and cerebral blood flow (CBF) were investigated. Under normoxia (arterial pO₂ ∼ 120 mm Hg), piO₂ was ∼30 mm Hg and jugular venous pO₂ was ∼50 mm Hg. During hyperoxia (arterial pO₂ = 90-300 mm Hg), piO₂ increased linearly with the arterial pO₂. Following hypercapnia (arterial pCO₂ = 20-60 mm Hg), the piO₂ increased sigmoidally with increasing CBF. With hypoxia (arterial pO₂ = 30-40 mm Hg), CBF increased ∼56% and piO₂ decreased to ∼15 mm Hg. The hypoxia-induced CBF increase was effective to some extent in compensating for the reduced piO₂. This methodology may prove useful for investigating cerebral piO₂ under pathologically or functionally altered conditions.