Reduction of functional neuronal connectivity in long-term treated hypertension

Anatomic imaging of patients with chronic well-treated hypertension has demonstrated dilatation of the lateral cerebral ventricles and left brain atrophy, whereas positron emission tomography has shown only subtle reductions in regional cerebral metabolic rates for glucose in some subcortical nuclei. To further explore the implications of the imaging changes, an analytic technique designed to determine functional neuronal connectivity between regions of interest (ROIs) was applied to the data on regional cerebral metabolic rates for glucose to determine if and where in the brain reduction of functional neuronal connectivity occurred.

Glucose metabolism was measured by positron emission tomography in 17 older men (age, 68 +/- 8 years) with well-controlled, noncomplicated hypertension of at least 10 years' duration and in 25 age- and sex-matched healthy control subjects. A significant correlation difference analysis was performed to determine which ROI pairs had reduced correlation coefficients (reduced functional neuronal connectivity). The vascular pattern of the reduction was determined after allocating the ROIs to their appropriate vascular territories.

Compared with the control subjects, hypertensive patients had reduced correlation coefficients in cortical territories of the internal carotid arteries but not of the vertebrobasilar arteries. The border zone supplied by the middle and anterior cerebral arteries was most affected.

The border zone between the anterior and middle cerebral arteries is vulnerable to ischemia from carotid pathology, systemic hypotension, or both. We hypothesize that although these hypertensive patients were "well controlled" and had normal neuropsychological tests, they may have experienced ischemia severe enough to cause border zone reduction of functional neuronal connectivity as a result of carotid pathology, antihypertensive medications, hypotensive episodes with a right-shifted autoregulation curve, or other factors in isolation or combination.