Cerebral Blood Flow and Cerebral Metabolic Rate of Oxygen Requirements for Cerebral Function and Viability in Humans

Abstract

Summary: This study was undertaken to determine the minimum CBF and CMR07 required by the human brain to maintain normal functio-n and viability for more than a few hours. Positron emission tomography (PET) was used to perform regional measurements in 50 subjects with varying degrees of cerebral ischemia but no evidence of infarction. There were 24 normal subjects, 24 subjects with arteriographic evidence of vascular disease of the carotid system, and two subjects with reversible ischemic neurological deficits due to cerebral vasospasm. Min imum values found in the 48 subjects with normal neu rological function were 19 mi/IOO g-min for regional ce rebral blood flow (rCBF) and 1.3 mi/IOO g-min for re gional cerebral metabolic rate of oxygen (rCMROJ). Minimum values for all 50 subjects with viable cerebral tissue were 15 ml/IOO g-min for rCBF and 1.3 mi/IOO gMeasurements of regional cerebral blood flow (reB F) in experimental animals subjected to focal cerebral ischemia have demonstrated the existence of two separate thresholds for ischemic neuronal damage. Electrocerebral activity diminishes at flows below 20 mlllOO g-min, whereas membrane failure and cell death do not occur until reBF falls below �10 mlllOO g-min (Jones et aI. , 198 1;Astrup, 1982;Heiss and Rosner, 1983; Branston et aI. , 1984). Values for reBF within this range of 10-20 mlllOO g-min have been correlated with reversible

Metabolic Crisis without Brain Ischemia is Common after Traumatic Brain Injury: A Combined Microdialysis and Positron Emission Tomography Study

“…In the first instance, we used the criterion of OEF40.75 and in the second we used the criteria of critical oligemia proposed by Coles et al (2004). Critical oligemia uses the concept that the lowest cerebral venous oxygen content (CvO 2 ) in an infarction is below the threshold of 3.5 mL/100 mL (Yundt and Diringer, 1997;Powers et al, 1985. Hence the formula for critical oligemia used was OEF crit ¼ (CaO 2 -3.5)/CaO 2 .…”

“…Indeed, a single valid OEF threshold for ischemia has not been agreed on in the literature. Alternatively, a reduction in CMRO 2 o1.4 mL/(100 mL/min À1 ) has been shown to be a threshold below which tissue viability is lost under conditions of ischemia (Powers et al, 1985;Ackerman et al, 1989). If we use this CMRO 2 definition of irreversibly injured tissue, then in the three subjects who displayed CMRO 2 r1.3, 2/3 had an LPR 440 and might be considered ischemic, while one did not.…”

“…To be independent of a single OEF threshold, we used an alternative definition of ischemia, namely CvO 2 o3/5 mL/100 mL, proposed by Powers et al (1985), Sutton et al (1990), and recently by Coles et al (2004). The CvO 2 -based analysis reveals that only 1% of all regions imaged were in the ischemic range.…”

Calibrated MRI to Evaluate Cerebral Hemodynamics in Patients with an Internal Carotid Artery Occlusion

“…The ability of the vasculature to modulate its tone through dilation or constriction is called the cerebrovascular reserve capacity, which is typically evaluated by measuring the cerebrovascular reactivity (CVR). 2 Upon exhaustion of the cerebrovascular reserve capacity, further reductions in perfusion pressure are countered by increasing the oxygen extraction fraction (OEF) 3 from arterial blood. When these mechanisms are not sufficient, the cerebral metabolic rate of oxygen (CMRO 2 ) will decrease and this can lead to tissue ischemia.…”

“…When these mechanisms are not sufficient, the cerebral metabolic rate of oxygen (CMRO 2 ) will decrease and this can lead to tissue ischemia. 1,3 Impaired CVR is a predictor for increased risk of ipsilateral stroke and transient ischemic attack (TIA) in patients with steno-occlusive carotid disease. 4,5 Similarly, increased OEF has been shown to predict recurrent ischemic stroke in patients with symptomatic occlusive disease of the cerebral vasculature.…”