Cognition in Elderly May Decline With High or Low Blood Pressure

Both higher and lower blood pressure may adversely affect cognitive performance among the elderly, although age, education level, alcohol consumption, and use of antihypertensive medications may influence those outcomes, according to a report from a long-term study of 847 elderly people.

“Increased awareness is needed that the brain is an early target organ of both high and low blood pressure before stroke and dementia,” Shari R. Waldstein, Ph.D., of the University of Maryland, Baltimore County, and colleagues reported in the March issue of the journal Hypertension.

“Younger age, higher levels of education, use of antihypertensive medications, and some alcohol use may protect against the neurobiological consequences of high blood pressure,” wrote the authors, all researchers with the Baltimore Longitudinal Study of Aging, a prospective study begun by the National Institute of Aging in 1958.

“Both high and low diastolic blood pressure were associated with poorer performance on tests of executive function and confrontation naming among less-educated persons; with tests of perceptuo-motor speed and confrontation naming among individuals not medicated with antihypertensives; and with executive function among older individuals.”

The researchers analyzed data from volunteer subjects dating back to January 1, 1986, and excluded those with dementia, cerebrovascular disease, or renal failure at baseline. The overall study uses a continuous recruitment process, so the number of individual visits varied; the average was 2.7 visits each. About 70 percent of the subjects were seen twice, and 52 percent had three visits.

Standardized blood pressure measurements were taken at each visit, and participants took standard neuropsychological tests. The Digits Forward and Backward parts of the Wechsler Adult Intelligence Scale–Revised assessed attention and working memory. The California Verbal Learning Test evaluated verbal learning and memory, and the Benton Visual Retention Test measured nonverbal memory. Attention, perceptuomotor speed, visuomotor scanning, and mental flexibility were assessed by the Trail Making Test, Parts A and B, while Letter Fluency and Category Fluency tests examined phonetic and semantic association fluency. The Boston Naming Test evaluated word finding. Results of these tests were plotted against curves of higher and lower diastolic and systolic blood pressure.

Participants under age 60 with higher systolic blood pressure made more errors on the Benton Visual Retention Test and did worse on the Boston Naming Test than those with normal systolic pressure, but improved over time, probably as a result of a practice effect, said Waldstein and colleagues. Among subjects aged 80 or older at baseline, those with higher systolic blood pressure produced declining scores on the same tests over time.

However, participants with lower education levels and either high or low diastolic blood pressure performed worse on the Boston Naming Test than those with a mid-range diastolic pressure, producing a U-shaped curve for the results. Among less-educated subjects, the Trail Making B test produced similar results, but scores were significantly worse for those with high diastolic pressure, creating a J-shaped curve.

Younger participants taking the Letter Fluency Test performed better if they had higher diastolic blood pressure. But among older persons, both high and low diastolic blood pressure predicted worse scores, compared with those with mid-range blood pressure. Nondrinkers with higher systolic blood pressure made more errors on the Benton Visual Retention Test than those who consumed alcohol.

Taking antihypertensive medications affected test results, too, wrote Waldstein and colleagues. Persons not on drugs to lower blood pressure scored more poorly on the Boston Naming Test at both high and low diastolic blood pressure levels, while their medicated counterparts performed similarly through all blood pressure ranges.

“Elderly persons may be most vulnerable to the cognitive consequences of higher systolic blood pressure over time,” the authors stated, based on the longitudinal decline on tests of nonverbal memory and confrontation naming.

Both high and low blood pressure has been associated with effects on cognitive function, said hypertension expert Vasilios Papademetriou, M.D., D.Sc., a professor of medicine at Georgetown University and director of hypertension and cardiovascular research at the Washington, D.C., Veterans Affairs Medical Center, in an interview. Diastolic blood pressure decreases with age, while systolic pressure rises as people get older. The reason is the same, though: arteries stiffen as part of the aging process. This divergence of systolic and diastolic pressure (called isolated systolic hypertension) is typical of advancing age and increases risk to the brain in several ways.

High blood pressure may cause cognitive declines by means of white matter disease, brain atrophy, small silent infarctions, atherosclerosis in cerebral or cervicocerebral arteries, or reduced cerebral blood flow. Low blood pressure may cause insufficient cerebral perfusion, with subsequent neuropathology, or may be related to cardiovascular comorbidities that could decrease cognitive function, suggested Waldstein and colleagues.

“It is possible that over time the cognitive and neurobiological correlates of hypotension and hypertension may progress to mild cognitive impairment and/or dementia,” they wrote. “This study... highlights the need to further understand factors that increase individuals' vulnerability to the cognitive consequences of high or low blood pressure.”

Until further research clarifies those relationships, clinicians should not hesitate to treat hypertensive patients out of fear that lowering diastolic blood pressure will induce cognitive dysfunction, Papademetriou noted.

“We have no information showing that lowering diastolic blood pressure is associated with dementia,” he told Psychiatric News. “Systolic blood pressure is associated with increased risk of stroke, and stroke is the strongest contributor to dementia and cognitive decline. Numerous studies over the last four decades have shown that optimal treatment of hypertension will prevent about 40 percent of strokes.”

Current national guidelines for a hypertension diagnosis—greater than 140/90 mm Hg, or for patients with diabetes and chronic kidney disease, greater than 130/80 mm Hg—and treatment are set out in the Seventh Report of the Joint National Committee on Prevention, Detection, Evaluation, and Treatment of High Blood Pressure (JNC 7), published by the National Heart, Lung, and Blood Institute, posted at<www.nhlbi.nih.gov/guidelines/hypertension>.

“Nonlinear Relations of Blood Pressure to Cognitive Function” by Waldstein and colleagues is posted at<http://hyper.ahajournals.org/cgi/content/abstract/45/3/374>. A report by Papademetriou, “Blood Pressure Regulation and Cognitive Function: A Review of the Literature,” is posted at<www.geri.com/geriatrics/article/articleDetail.jsp?id=142621>.▪

Hypertension 2005 45 374