CHICAGO — Individuals with both Alzheimer's disease and hypertension had significantly lower blood flow in multiple regions of the brain on magnetic resonance imaging, compared with their counterparts without hypertension, investigators reported in a poster at the annual meeting of the Radiological Society of North America.
In the study of 88 participants with a mean age of 83 years, brain perfusion also was significantly lower in controls with normal cognitive function and hypertension, compared with their counterparts without hypertension. A trend toward lower perfusion in individuals with mild cognitive impairment and hypertension did not achieve statistical significance.
The data are consistent with recent studies showing that Alzheimer's patients with vascular disease in general had faster progression of symptoms, Dr. Oscar L. Lopez said in an interview. In addition, multiple studies in the literature have shown that hypertension—especially in midlife—is a risk factor for Alzheimer's disease.
The same researchers also recently showed that normal subjects with hypertension had diminished cerebral blood flow in cerebral areas that are usually involved in Alzheimer's disease (Stroke 2008 Jan. 3[doi:10.1161/STROKEAHA.107.495457]). This does not mean that all individuals with hypertension will develop dementia, but in those who are destined to have Alzheimer's disease, dementia symptoms may appear earlier than in those without hypertension, said Dr. Lopez, who is a professor of neurology at the University of Pittsburgh and principal investigator in the Cardiovascular Health Study (CHS) Cognition Study.
“Both studies emphasized the importance of adequate treatment for hypertension,” he said. “In cognitively normal individuals, hypertension treatment may delay the onset of the dementia, and in Alzheimer's disease patients, it may ameliorate the rate of decline.”
Study participants were recruited from the ongoing CHS Cognition Study, and included 48 controls with normal cognitive function (including 10 with hypertension), 20 individuals with Alzheimer's (including 10 with hypertension), and 20 individuals with mild cognitive impairment (including 10 with hypertension). Hypertension, defined as a blood pressure greater than 140/90 mm Hg, was treated in all patients.
All participants were scanned with T1-weighted and arterial spin-labeled MRI at 1.5T. This quantitative technique uses no external contrast and uses kinetics modeling equations to compute cerebral blood flow based on MR signal intensity. Cerebral blood flow values are expressed in milliliters of blood per 100 g of tissue per minute, said lead investigator Cyrus Raji, who is a student at University of Pittsburgh, where the study was conducted. The study was funded by the National Institute on Aging, and no relevant financial conflicts of interest were disclosed.
Overall, cerebral blood flow was lowest in individuals with Alzheimer's disease and hypertension (34.8 mL per 100 g/min), compared with controls with hypertension (41.4) and those with mild cognitive impairment and hypertension (47.8).
Notably, decreased flow in Alzheimer's participants with hypertension occurred in the posterior cingulate gyrus (35.9), lateral prefrontal cortex (29.5), and left thalamus (28.9). Corresponding cerebral blood flow values were 52.3, 39.4, and 38.5 for hypertensive controls and 47.8, 36.3, and 58.1 for hypertensive participants with mild cognitive impairment (MCI).
Cerebral blood flow to the left hippocampus was reduced in participants with hypertension in the Alzheimer's (33.5), control (38.7), and MCI (47.7) groups, compared with their counterparts without hypertension (41.2, 42.4, and 57.2, respectively). This finding may have implications for Alzheimer's development, because the hippocampus is an early site of Alzheimer's pathology.
Hypertension and brain vascular disease may be major risk factors for dementia, said senior author Dr. Louis Kuller, also of the University of Pittsburgh, in an interview. “Excellent control of elevated blood pressure or prevention of hypertension, especially in 'middle ages' prior to vascular brain damage, may be the most important preventable determinant for dementia.”