Effects of 2% carbon dioxide, 0.5% carbon dioxide, and 100% oxygen on cranial blood flow of the human neonate.

The effects of breathing 100% O2, 2% CO2, and 0.5% CO2 on the cranial blood flow of the normal human baby were investigated. A mercury in Silastic strain gauge was placed around the occipital head circumference (OFC) of a sleeping infant, and jugular flow was measured using venous occlusion plethysmography. Cranial flow was calculated using formulas derived from an electrical model. In matched sleep states cranial blood flow fell with 100% O2 (mean from eight babies = 32.8%), and rose with 2% CO2 (mean from seven babies = 40.6%). With 0.5% CO2 the flow rose in three babies and did not change in another four. These results indicate the extreme sensitivity of cerebral vasculature to the nature of the ambient gas.