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Neuroradiological functional imaging techniques demonstrate the patterns of hypoperfusion and hypometabolism that are thought to be useful in the differential diagnosis of Alzheimer's disease (AD) from other dementing disorders. Besides the distribution patterns of perfusion or energy metabolism, vascular transit time (VTT), vascular reactivity (VR), and oxygen extraction fraction (OEF), which can be measured with positron emission tomography (PET), provide hemodynamic aspects of brain pathophysiology. In order to evaluate the hemodynamic features of AD, PET studies were carried out in 20 patients with probable AD and 20 patients with vascular dementia (VaD). The PET findings were not included in their diagnostic process of AD. Using oxygen-15-labeled compounds, cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO(2)), OEF, cerebral blood volume, and VTT were measured quantitatively during resting state. To evaluate VR, CBF was also measured during CO(2) inhalation. There was a significant increase in OEF in and around the parietotemporal cortices, but both VTT and VR were well preserved in patients with AD. By contrast, VR was markedly depressed and VTT was mildly prolonged in patients with VaD. Thus, from the hemodynamic point of view, the preservation of vascular reserve may be a distinct difference between AD and VaD. Furthermore, this indicates a hemodynamic integrity of the vasculature in the level of arterioles in AD.

To elucidate the hemodynamic pathophysiology underlying Alzheimer's disease (AD), cerebral blood flow (CBF), cerebral metabolic rate of oxygen (CMRO2) and oxygen extraction fraction (OEF) were measured with positron emission tomography in 10 patients with probable AD and in 20 age-matched normal volunteers. By the 15O intravenous bolus injection method, CBF was measured during resting state, CO2 inhalation (hypercapnia) and hyperventilation (hypocapnia), and the vascular reactivity (VR) was estimated by comparing the CBF changes (delta CBF%/PaCO2 mmHg) in the hyper- or hypocapnic to the resting state. By the 15O2 single-breath method or 15O steady-state method, CMRO2 and OEF were measured during resting state. Based on 26 regions of interest, local CBF, CMRO2 and OEF were compared statistically between the two groups. As compared with the control group, the mean CBF and CMRO2 decreased to as low as 77.0% and 88.4% of the normal values, respectively, while the mean OEF increased by 12.1% (p < 0.05) in AD patients. These changes were most pronounced in the supramarginal and superior temporal gyri. There was no focal change in VR in the AD group, and no significant difference was seen in VR to either hyper- or hypocapnia between AD and control groups. The results may suggest a vascular involvement, possibly at the capillary level, that might cause a relative misery perfusion syndrome accompanied by preserved vascular reactivity in AD.