Cerebral blood flow autoregulation: Effect of hypercapnia on cerebral tissue gas concentrations

Cerebral tissue oxygen and carbon dioxide tensions were monitored continuously in six rhesus monkeys using a Teflon coated catheter and a medical mass spectrometer. The monkeys were exposed to several ambient gas mixtures in a sealed helmet. Gases included air, 12% oxygen in nitrogen, and 12% oxygen with 5% carbon dioxide in nitrogen. Twelve percent oxygen in nitrogen resulted in a marked decrease in tissue pO 2 to 5.0 ± 2.2 mm Hg from a control of 16.5 ± 2.9. The addition of 5% carbon dioxide to the 12% oxygen provided almost complete amelioration of the decline in tissue pO 2 with a mean value of 15.7 ± 0.5 mm Hg.