Investigation of the Cerebrovascular Reserve Capacity to Identify Patients with Chronic Brain Ischemia Who May Benefit from Bypass Surgery

Abstract

In response to the result of the EC-IC bypass study [8], which failed to show any benefit for the prevention of cerebral ischemia in the surgical group, it has been argued that surgery has been overused. Accordingly, it has been suggested that only so-called hemodynamic cases, with a decreased cerebral perfusion pressure due to insufficient collateral blood supply, should be candidates for cerebral revascularization. The identification of these hemodynamic cases, however, is not possible when using clinical criteria and is still difficult on the basis of diagnostic studies such as angiography or CT scanning of the brain. Positron emission tomography (PET), on the other hand, which undoubtedly provides superior information on cerebral circulation and metabolism is not readily available. Therefore, we have used regional cerebral blood flow (rCBF) studies, under stimulated conditions with the Diamox test, in order to investigate the regulatory capacity of the cerebral circulation [7]. These studies were performed before and after bypass surgery in order to find out whether there was any improvement of the cerebrovascular reserve capacity following surgery which could then be regarded as evidence in support of the beneficial effect of the operation in these patients.