Vascular and metabolic reserve in Alzheimer's disease

Vascular and metabolic reserve were analyzed in probable Alzheimer's diseas e (AD) and vascular dementia (VaD). Cerebral blood flow (CBF), cerebral blo od volume (CBV), cerebral metabolic rate of oxygen (CMRO2), and oxygen extr action fraction (OEF) were measured quantitatively with positron emission t omography (PET). Vascular reactivity (VR) was also calculated by comparing the CBF during 5% CO, inhalation with the CBF during normal breathing. Vasc ular transit time (VTT) that was calculated as a ratio of CBV/CBF and VR re flect vasodilating capacity of the small resistance vessels, whereas OEF de signates metabolic (oxygen-extraction) reserve in threatening brain ischemi a. Significant increase in OEF was seen in the parieto-temporal cortex and both VTT and VR were preserved in AD patients. By constrast, there was no s ignificant increase in OEF whereas VTT was prolonged and VR was markedly de pressed in VaD patients. The increase of OEF and preserved VTT and VR seen in AD patients indicate the possible participation of vascular factors in t he pathogenesis of AD perhaps at the capillary level. (C) 2000 Published by Elsevier Science Inc. All rights reserved.