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High Blood Pressure Does Not
Accelerate Age-Related Cognitive Decline
DURHAM, N.C., Sept. 29,
2003 -- 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. |
