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

Abstract

SUMMARY 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 (CMRO 2 ). In the whole group of patients, both CBF and CMRO, 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-CMRO 2 couple again resulting in increases in CMRO 2 . 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. Stroke Vol 16, No 4, 1985 THE CONTINUOUS OXYGEN 15 INHALATION METHOD provides a regional measurement of the cerebral blood flow (CBF) and oxygen metabolic rate (CMRO,). Earlier semi-quantitative studies carried out by this method 1 -2 showed the disappearance, after an extra-intracranial by-pass operation (EIAB), of two different patterns of focal functional anomaly. The first one, termed misery-perfusion, consists of a lowered CBF and an increased oxygen extraction fraction (OEF) downstream from a carotid occlusion. This pattern reflects the relative maintenance of the CMRO, and was interpreted as evidence of a drop in the cerebral perfusion pressure to a point beyond the lower threshold of CBF auto-regulation. For the second type, involving a reduced CBF with no rise in the OEF, no satisfactory pathophysiological interpretation was put forward. 2However in these semi-quantitative studies it was possible neither to measure the CMRO, nor to detect bilateral effects of the EIAB, both of which objectives form the centre of present work. Patients and MethodsThe study involved 12 consecutive patients in whom the permeability of the EIAB was verified. One preoperative study was an isolated CBF measurement (case No. 3). Eleven of these patients suffered from internal carotid artery (ICA) obstruction and the last a middle cerebral artery (MCA) occlusion. Mean age was 56 ± 9.3 years.Individual clinical, angiographic and CT Scan data Received July 16, 1984; revision #1 accepted December 7, 1984. are summed up in table 1. The advisability of EIAB was judged on the basis of clinical and angiographic criteria, independently of pre-operative PET results. Clinical signs of "hemodynamic" ischemia was the deciding factor in 5 cases (patients No. 5,6,9,11,12) ...

Extracranial-intracranial bypass for ischemic cerebrovascular disease: what have we learned from the Carotid Occlusion Surgery Study?

“…12 This criticism was likely invalid given that multiple groups have reported that STA-MCA cortical branch anastomosis can reverse an abnormally elevated oxygen extraction fraction (OEF). 6,17,33,39 Second, many of the highest-risk patients may have been operated on outside of the trial and, therefore, not included in the study results, leading to a selection bias. 3,42 This claim was conclusively refuted by further data provided by the EC-IC Bypass Trial Investigators.…”

Paradoxical reduction of cerebral blood flow after acetazolamide loading: a hemodynamic and metabolic study with 15O PET

“…In the contralateral hemisphere of the low CBF b subgroup, metabolic reduction was considered to be attributable to trans-hemispheric functional depression. Recovery of CMRO 2 in the contralateral hemisphere after bypass surgery supports this view [38] .…”

Oxygen Extraction Fraction at Maximally Vasodilated Tissue in the Ischemic Brain Estimated from the Regional CO2 Responsiveness Measured by Positron Emission Tomography

“…manipUlate the absolute value of OEF in relation to these pathophysiological circumstances (Baron et al, 1983;Wi se et al, 1983;Powers et al, 1984;Samson et al, 1985).…”