Blood flow to the parts of the brain that support memory function differs between people with high blood pressure and those with normal blood pressure, and this difference seems to increase when high blood pressure is treated with medications, researchers reported today at the American Heart Association's 61st Annual Fall Conference of the Council for High Blood Pressure Research.
"It does not mean that those with high blood pressure were remembering significantly less; rather, the brain areas acting together during memory required more blood flow to remember the same things as people who did not have high blood pressure in the study," said lead author J. Richard Jennings, Ph.D.
In a previous study, Jennings and colleagues found that people with hypertension differed from those without hypertension in the amount of brain tissue activated during memory tasks.
"In this study we wanted to find out if treating people for high blood pressure would change that pattern of activation," said Jennings, a professor of psychiatry and psychology at the University of Pittsburgh School of Medicine in Pittsburgh, Pa.
The researchers assessed the brain blood flow of 28 adults with untreated hypertension while they were doing a memory task. The researchers then randomly divided the subjects into two hypertension treatment groups. Half received the angiotension-converting enzyme inhibitor lisinopril; the other half received the beta-blocker atenolol. Subjects took the medication for a year before researchers tested them in the same way, again monitoring their blood flow to the brain as they did the memory task.
Jennings and colleagues were surprised to find that taking either antihypertensive medication actually increased the inefficiency of the brain's work during memory. He explained that, when doing memory tasks, four areas of the brain become active in different ways: the thalamus, posterior parietal, prefrontal area and hippocampus.
"In the first study, we looked at the correlation between the activation of those areas. We wanted to see if the areas tend to be activated in a correlated way; so, if you had a lot of activation in the prefrontal area, did you also have a lot of activation in the parietal area"" he said. "When we asked that question in our first study, we found out that the correlation in those areas was higher in people with high blood pressure than it was in people who didn't have high blood pressure. That means that more brain tissue was getting coordinated during the memory task in people with high blood pressure than in those with normal blood pressure.
"After a year of treatment for their high blood pressure, we expected that we'd find that the correlation between those areas actually would decrease; so, the patients treated with hypertensive medication would look more like those with normal blood pressure. Instead, the correlation actually increased. After treatment the hypertensive patients were activating even more blood flow to those areas at the same time," Jennings said.
According to Jennings, the coordination between brain areas doing the memory task was more than twice as much in the hypertensive patients after treatment as compared to before treatment--and this difference was even bigger compared to people without hypertension.
"Further research is needed to find out what this means to memory function, and whether having hypertension and taking antihypertensives might have the unanticipated effects of changing brain function and causing mental fatigue," he said.
"This research is reassuring to those concerned about hypertension therapy's adverse effects, particularly cognitive effects. Treating hypertension is not only beneficial for extending life, but also for improving the quality of life," said Daniel W. Jones, M.D., American Heart Association President, Vice Chancellor for Health Affairs, Dean, School of Medicine, and Herbert G. Langford Professor of Medicine, University of Mississippi Medical Center.
Co-authors are Matthew Muldoon, M.D.; Israel Christie, Ph.D.; Julie Price, Ph.D. and Carolyn Meltzer, M.D. The study was funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health.
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