Misery perfusion with preserved vascular reactivity in Alzheimer's disease.

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.

Regional correlations between the EEG and oxygen metabolism in dementia of Alzheimer's type.

To determine the relationship between EEG slowing and cerebral hypometabolism in dementia, 10 patients with dementia of Alzheimer's type (DAT) were evaluated with quantitative topographic EEG and positron emission tomography (PET). Power in each 1-Hz frequency band from 2-20 Hz, power ratio index, and normalised PET data from corresponding cortical sites were compared to data obtained from 20 normal volunteers. PET revealed significant parieto-temporal hypometabolism, and topographic EEG mapping and power spectrum analysis revealed a slowing of the background EEG that was most pronounced in the parietal-temporal areas. Correlation analysis between EEG power spectrum data and CMRO2 revealed significant negative correlations for frequencies below 8 Hz and significant positive correlations above 8 Hz in the parieto-temporal regions, which have previously been identified as the areas most severely affected by pathological changes associated with DAT. Correlation coefficients plotted as functions of frequency illustrated the relationships between EEG changes and reduced CMRO2, supporting previous views that EEG slowing in DAT may be related to hypometabolism in cortical regions most affected by the disease.

Scalp topography of SEP late components in patients with supra-tentorial lesions.

Somatosensory evoked potentials (SEP) to simultaneous bilateral median nerve stimulation were recorded in 7 patients with unilateral brain lesions, 8 patients with degenerative dementia, and 5 normal volunteers. Right-left amplitude difference was compared from serial topographic images and the amplitude was compared at homologous electrodes. In patients with unilateral lesions, the amplitude from the frontopolar, frontal, anterior-temporal, and/or occipital electrodes was smaller on the affected side at 240 and 360 msec, regardless of whether the subjects showed sensory deficit or not. No significant laterality was seen in the primary sensorimotor areas. Distribution obtained from the patients with degenerative dementia was quite symmetrical. A significant right-left amplitude difference was seen at the anterior temporal site at 180 and 240 msec in normal controls, although an almost symmetrical distribution was obtained on the topographic images. The late components of SEP are not associated with the primary somatosensory function, but possibly with other cortical pathways.