Cerebral circulation

Abstract: The brain is critically dependent on a continuous supply of blood to function. Therefore, the cerebral vasculature is endowed with neurovascular control mechanisms that assure that the blood supply of the brain is commensurate to the energy needs of its cellular constituents. The regulation of cerebral blood flow (CBF) during brain activity involves the coordinated interaction of neurons, glia, and vascular cells. Thus, whereas neurons and glia generate the signals initiating the vasodilation, endothelial cells, pericytes, and smooth muscle cells act in concert to transduce these signals into carefully orchestrated vascular changes that lead to CBF increases focused to the activated area and temporally linked to the period of activation. Neurovascular coupling is disrupted in pathological conditions, such as hypertension, Alzheimer disease, and ischemic stroke. Consequently, CBF is no longer matched to the metabolic requirements of the tissue. This cerebrovascular dysregulation is mediated in large part by the deleterious action of reactive oxygen species on cerebral blood vessels. A major source of cerebral vascular radicals in models of hypertension and Alzheimer disease is the enzyme NADPH oxidase. These findings, collectively, highlight the importance of neurovascular coupling to the health of the normal brain and suggest a therapeutic target for improving brain function in pathologies associated with cerebrovascular dysfunction.

Abstract: During the past decade, technological advances have made it possible to measure regional cerebral hemodynamics in individual patients. Studies performed with these techniques have demonstrated that the degree of carotid stenosis correlates poorly with the hemodynamic status of the ipsilateral cerebral circulation. The primary determinant of cerebral perfusion pressure and blood flow under these circumstances is the adequacy of collateral circulatory pathways. Since collateral circulation varies from patient to patient, there is no critical degree of carotid stenosis that consistently produces hemodynamic compromise of the cerebral circulation. It is, thus, time to abandon the concept of the hemodynamically significant carotid stenosis as it relates to the pathogenesis and treatment of cerebrovascular disease. Measurement of regional cerebral hemodynamics have provided new insight into the pathogenesis of tranisent ischemic attacks and generated some preliminary data on the prognostic and therapeutic importance of chronic reductions in regional cerebral perfusion pressure. Further investigations into the importance of hemodynamic factors in ischemic stroke can now be based on accurate assessment of cerebral (not carotid or vertebrobasilar) hemodynamics in the context of other coexisting epidemiological, clinical, hematological, and angiographic risk factors.

Abstract: Faraci, Frank M., and Donald D. Heistad. Regulation of the Cerebral Circulation: Role of Endothelium and Potassium Channels. Physiol. Rev. 78: 53–97, 1998. — Several new concepts have emerged in re...