Regional Cerebral Blood Flow Determination by the Hydrogen Clearance Technique and Comparison With Oxygen Availability in the Rabbit

Abstract

Hydrogen clearance using the tissue polarographical electrode appears to be a potentially useful technique for intermittent measurements of rCBF in relatively small areas. Both chronic and acutely implanted electrodes were placed at different depths in rabbit cerebrum including cortex and subcortical gray and white matter. Polarographical electrodes, oppositely charged, sensing oxygen availability (O ₂ a) also were implanted proximately for comparison of both rCBF response and O ₂ a under conditions of normocapnia and hypercapnia. No functional difference was discerned between chronic and acute electrodes. Generally rates of blood flow were faster in gray matter than in white. Both monoexponential and biexponential curves, representing one and two compartments of blood flow, respectively, were observed in both gray and white matter. Some three-compartment curves also were seen. Hypercapnia generally induced faster rCBF in all compartments as well as increased O ₂ a. Occasionally a change in compartmentalization was recorded from a single electrode during hypercapnia, and two instances of paradoxical decrease in rCBF were observed. A multicompartmental model with an arteriovenous thoroughfare shunt was postulated to account for the wide range of blood flow values recorded: from 5.2+ to 0.2 ml per gram per minute.