Comparison of 85krypton and 133xenon cerebral blood flow measurements before, during, and following focal, incomplete ischemia in the squirrel monkey.

Abstract

A comparison of regional cerebral blood flow measurements made with beta- and gamma-emitting isotopes revealed good correspondence in areas of normal perfusion and reactive hyperemia but poor correspondence in areas of focal ischemia. After middle cerebral artery occlusion at normocapnia, there was a 65% reduction in regional cerebral blood flow from 1.40 plus or minus 0.27 ml/g min--1 to 0.49 plus or minus 0.10 ml/g min--1 in monkeys studied with 85Kr but only a 27% reduction in regional cerebral blood flow from 0.84 plus or minus 0.09 ml/g min--1 to 0.61 plus or minus 0.08 ml/g min--1 in monkeys studied with 133Xe. The lack of correlation within areas of focal, incomplete ischemia was attributed to an impairment of isotope delivery to the area of ischemia coupled with the inherent lack of spatial resolution of determinations made with 133Xe. This finding may partly explain the numerous discrepancies in experimental and clinical studies of the effects of alterations in the arterial partial pressure of CO2 on regional cerebral blood flow in areas of ischemia; it may also explain the failure of such studies to reflect the true severity of focal ischemia.

Influence of Cerebral Vasoconstricting and Vasodilating Agents on Blood Flow in Regions of Focal Ischemia

“…The GeigerMiiller probe recorded beta particles originating from very superficial layers of the brain and did not detect significant activity from a depth greater than 2.5 mm. 15 This is consistent with the characteristics of the indicator and is accepted by most workers in the field. 34 - 35 Consequently, rCBF within the area of focal, incomplete ischemia is accurately measured and the errors of "look through" and Compton scatter are eliminated.…”

Effects of Clonidine on Cerebral Blood Flow and the Response to Arterial CO2

“…In the case of Xe, a 'Y emitter, the isoresponse curve for the scin tillation detector is a narrow, truncated cone with 75% of the count arriving 1 cm from the detector surface and 50% of the count arriving 2.1 cm from the detector surface. In the case of Kr, a (3 emitter, a Geiger-Muller tube is used that measures (3 ac tivity coming from a discrete volume of tissue 2.0 mm in depth (Hanson et al, 1975). Thus, we pre sume that changes in CBF detected by Kr clear ance reflect changes proximal to the pial surface, whereas Xe clearance detects flow through the gray matter, white matter, and large thoroughfare vessels.…”

“…Thus, we pre sume that changes in CBF detected by Kr clear ance reflect changes proximal to the pial surface, whereas Xe clearance detects flow through the gray matter, white matter, and large thoroughfare vessels. Moreover, owing to the "look-through phenomenon" and "Compton scatter" described previously (Hanson et al, 1975), changes in CBF in superficial layers may go undetected when Xe clearance is employed. It should be stressed that these changes do not reflect an effect on extra cranial perfusion.…”

In vivo Studies on Intracellular pH, Focal Flow, and Vessel Diameter in the Cat Cerebral Cortex: Effects of Altered CO2 and Electrical Stimulation

“…The isoresponse curve of the detector system in the cat preparation is a truncated cone with 50 and 90% of the count deriving 10 mm and 2 mm, respectively, from the detector surface. Energy levels were set on a single channel analyzer to minimize Compton scatter (Hanson et al , 1975). As with the Urn clearance.…”