DURHAM, N.C. -- Duke University Medical Center researchers have found that contrary to the classical model of aging, increased blood pressure does not accelerate the age-related decline in performing certain mental tasks.
Furthermore, the researchers reported, middle-aged subjects with high blood pressure showed more of a slowing in cognitive performance tests than did older adults with high blood pressure.
According to the researchers, past studies have been epidemiological in nature and have hinted that hypertensive patients perform worse than individuals with normal blood pressure on cognition tests, as measured by the speed of mental processing, attention, and memory tasks. However, unlike the new Duke study, which was performed in a laboratory setting, previous studies have been unable to tease out relationships between elevated blood pressures and age on specific cognitive tasks.
The results of the Duke experiments were published today (Sept. 29, 2003) in the September issue of the journal Aging, Neuropsychology and Cognition. The study was supported by the National Institutes of Health.
"While the changes in cognitive performance associated with elevated blood pressure seen in our experiments were statistically significant, they are unlikely to interfere with mental functioning during everyday life," said Duke's David Madden, Ph.D., cognitive psychologist and researcher in aging. "However, the changes we recorded in the laboratory may represent a situation that could become clinically significant when other diseases, especially those that are cardiovascular in nature, are included.
"The significance of these cognitive effects will become clearer as additional evidence is obtained regarding the changes in brain structure and function that typically accompany chronically elevated blood pressure," Madden said.
Unlike the previous studies, where patients often had other diseases and might have been on medications, the Duke team focused exclusively on participants who had high blood pressure, but who were not taking any medications. None of the participants had detectable cardiovascular disease.
"We know that in general, hypertension increases with age," Madden said. "Our goal was to determine if there was any effect of elevated blood pressure on the natural course of healthy aging."
For their experiments, the Duke team recruited 96 adult volunteers - 48 with unmedicated high blood pressure and 48 with normal blood pressure. The patients were then equally divided into three groups: young (20-39), middle-aged (40-59) and older (60-79). Blood pressures were taken at regular intervals throughout the course of the experiments.
The tests, which were taken on a personal computer, measured how quickly participants could correctly respond in two general areas - visual search tasks and memory search tasks. In both cases, the stimuli on the computer screen were different combinations of 20 white consonants on a black background.
For the visual search tasks, participants had to view a pair of letters, and then after a period of time, had to quickly determine which one of that pair was present within displays of four to six letters. For the memory task, participants viewed either four or six letters, and then after a period of time, two letters appeared on the screen. Participants had to indicate which one of the letters was within the original group. Each participant underwent 640 trials.
"The results of our experiments show that the interaction between the effects of blood pressure and adult age do not support the predictions of the classical model, which holds that increasing blood pressure accelerates the decline in intelligence tasks," Madden said. "Our analysis of response times found that a decline in the high blood pressure group was only evident for the middle-aged group, but not for the youngest or oldest participants."
Additionally, the team found that increasing age was associated with specific deficits in performing search tasks above and beyond what would have been expected, whereas increasing blood pressure was not associated with these deficits, Madden continued.
The differences in performance between the high blood pressure group and the normal blood pressure group were more closely related to the overall level of difficulty of the task rather than to short-term memory demands, he added.
Duke colleagues on the study were Linda Langley, Rebecca Thurston, Wythe Whiting, Ph.D. and James Blumenthal, Ph.D.