Regional Cerebral Blood Flow by 133 Xenon Inhalation: Preliminary Evaluation of an Initial Slope Index in Patients with Unstable Flow Compartments

Abstract

Repeated measurements of regional cerebral blood flow (rCBF) were made by the short (ten minutes) 133 Xenon inhalation technique and bicompartmental analysis in 11 patients with cerebrovascular disorders, mainly acute cerebral infarction. rCBF was measured 3 to 11 times during one to two weeks. The blood flow of the fast compartment (f 1 ) was calculated as well as the relative weight of this compartment (w 1 , assumed to correspond to gray matter). In addition a new flow index, the Initial Slope Index (ISI) modified for the inhalation technique, was used. This index of predominantly gray matter flow was calculated from a one-minute epoch of the early part of the clearance curve corrected for recirculation. In three of the patients the f 1 and ISI varied in parallel and the w 1 showed generally only minor variations from one measurement to the other. However, in the other eight patients fluctuation of the w 1 and f 1 values were seen which often showed no meaningful relation to the clinical course. The observed w 1 changes indicated that some tissues (slowly perfused gray matter and/or rapidly perfused white extracerebral tissues) fluctuate between the fast and the slow compartment. In such cases the f 1 values obtained cannot be used for comparison between measurements, since they represent flow rates of varying tissues and do not always represent a true gray matter blood flow. In these patients the ISI, which is independent of such weight changes, showed moderate and clinically likely variations.