Effects of extra-intracranial arterial bypass on cerebral blood flow and oxygen metabolism in humans.

Twelve patients, eleven with a carotid obstruction and one with an occlusion of the middle cerebral artery, were studied before and after a successful unilateral extra-intracranial arterial by-pass, (EIAB) using PET and the 15-0 steady-state technique to measure regional cerebral blood flow (CBF), oxygen extraction fraction and oxygen metabolic rate (CMRO2). In the whole group of patients, both CBF and CMRO2 increased significantly on both cerebral hemispheres after EIAB, returning toward control levels defined in age-matched subjects. Mean oxygen extraction fraction, on the other hand, was not affected. Individually, three different effects of EIAB emerged: 1) Alleviation of a state of long standing unilateral "misery-perfusion", as reported earlier; 2) parallel increase of CBF and CMRO2 bilaterally, which appeared due to improvement of a hemodynamic depression of metabolism, the precise mechanism of which remains obscure; 3) Complex, unexpected changes in the CBF-CMRO2 couple again resulting in increases in CMRO2. This metabolic improvement afforded by EIAB in our patients has not been reported before; it suggests that long-standing hemodynamic failure may induce a metabolic depression that is still potentially reversible by surgical revascularization.