Regional cerebral and extracranial blood flow measurements in acutely and chronically implanted cats: hydrogen clearance technique.

A technique is described for measuring regional blood flow concomitantly in the brain and in extracranial tissues of the cat. Hydrogen clearance using the tissue polarographic electrode appears to be a useful technique for intermittent measurements of cerebral blood flow (CBF) in relatively small areas. H2 was administered by inhalation for 10 min. Both chronic and acutely implanted electrodes were placed at different depths in the cat brain, on the surface of the cortex, and in extracranial tissues. Clearance rates in gray matter of 75 to 119 ml/min/100 g tissue have been obtained and of 11 to 14 ml/min/100 g tissue in white matter. Clearance curves have invariably been monoexponential in character in white matter and biexponential in gray matter. Successful recordings of H2 clearance curves were obtained from both chronically (up to 5 months) and acutely implanted electrodes. A new type of electrode is described. The "paperclip" electrode is placed at the surface of the cortex, has a reactive surface much greater than that of needle electrodes, thus limiting the possible variations due to vascularization differences from one local area to the next, and induces no damage to the brain tissue. To test the reliability of the technique, blood flow was measured during hypercapnia and progressive exsanguination. All electrodes indicated increased rCBF following 5-7% CO2 inhalation. A marked decrease in blood flow was seen with peripheral electrodes during exsanguination, whereas it was necessary to lower arterial blood pressure by more than 60% of the baseline value to record decreased flow in brain tissues. The constancy of response from electrodes and the lack of obvious tissue damage on dissection of the brain renders the method an adequate one. It provides highly focal recording of both CBF and extracranial flow in chronically implanted animals.