Regional Cerebral Blood Flow by 133 Xenon Inhalation

Abstract

Repeated measurements of regional cerebral blood flow (rCBF) were made by the short (ten minutes) ¹³³Xenon 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 (f₁) was calculated as well as the relative weight of this compartment (w₁, 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 f₁ and ISI varied in parallel and the w₁ showed generally only minor variations from one measurement to the other. However, in the other eight patients fluctuation of the w₁ and f₁ values were seen which often showed no meaningful relation to the clinical course. The observed w₁ 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 f₁ 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.