Abstract WP227: Magnetic Resonance Measurement Of Static Global And Regional Cerebral Autoregulation

Abstract

Background: Reliable methods used to test static cerebral autoregulation are time-consuming and/or invasive. Objectives: To evaluate if noninvasive magnetic resonance measured oxygen extraction fraction (OEF), cerebral blood flow (CBF), and oxygen metabolic index (OMI=CBF×OEF) can consistently detect expected physiological changes in humans under normal and 10-15% lowered mean arterial pressure (MAP). Methods: Static cerebral autoregulation was determined by measuring changes in CBF using a pseudo continuous arterial spin labeling (pCASL) approach and Oxygen Extraction Fraction (OEF) using MRI T2‘-weighted asymmetric spin echo echo-planar imaging (EPI) sequences, in response to 10-15% reductions in MAP in stroke-free controls induced by using IV Nicardipine. Images were acquired in 3T MR scanner (Trio, Siemens Medical Systems Inc). Autoregulation was measured globally and regionally in the anterior (ACA), the middle (MCA) and the posterior cerebral artery (PCA) territories of the brain manually defined using autopsy based model. Autoregulatory Index (AI) was computed (AI = %CBF change/% MAP change) supplemented by CBF associated OEF changes. Baseline regional CBF and OEF, AI, CBF and OEF changes to 10-15% lowering of MAP Results: Nineteen normal volunteers (mean age 30, 95% male, 50% white, 40% black, 10% others) were consented to the protocol approved by the institutional review board. MAP lowering was successfully achieved in all subjects (Mean ± standard deviation of MAP lowering of 12.5 ± 5.6 mm Hg). At a global level this resulted in no significant change between pre-MAP lowering CBF (56.0 ± 8.5 ml/100g/min) and post-MAP lowering CBF (55.9± 8.8 ml/100g/min). This translated to a AI of 0 ± 1.2. The CBF results corroborated with no significant change in OEF and OMI. Baseline regional CBF was higher in the MCA territory (66.1 ± 7.6 ml/100g/min) compared with the ACA territory (52.8 ± 8.6ml/100g/min, p<0.001). The AIs were consistent (ANOVA p=0.15) at regional levels across ACA (-1.5 ± 3.1), MCA(-0.3± 2.1) and PCA (-0.1 ± 1.4) territories. Conclusions: Global and regional static cerebral autoregulation can be measured using MR measurement of CBF, OEF and OMI, before and after 10-15% reductions in MAP in healthy volunteers.