But this isn't possible using clinical blood pressure readings taken in a doctor's office or other health care setting.
So-called "ambulatory" blood pressure is measured using a special portable device that monitors blood pressure at regular intervals while patients go about their daily activities.
In the new study researchers compared changes in blood pressure and the volume of "white matter hyperintensities" - lesions that are a sign of small vessel brain damage - in the brains of 72 people, average age 82, at the start of the study and again two years later.
Previous studies have shown that white matter hyperintensities, which can be detected using MRI, are associated with a reduction in memory and thinking skills, known as cognitive decline. Along with looking for white matter hyperintensities, the researchers assessed the participants' cognitive ability and physical mobility over the two years.
The study found that a worsening in ambulatory blood pressure was associated with an increase in the brain lesions and a decrease in cognitive function and physical mobility. There was no association between white matter hyperintensities and clinical blood pressure readings, according to the findings published an issue of the journal Circulation.
"This study showed for the first time in an older population that blood pressure measured over a 24-hour period was associated with the progression of vascular brain disease, whereas the typical office blood pressure was not," senior author Dr William B. White, a professor of hypertension and clinical pharmacology in the Calhoun Cardiology Center at the University of Connecticut School of Medicine in Farmington, said in a news release from the American Heart Association.
Targeting average ambulatory blood pressure could reduce the progression of small vessel brain disease, according to the researchers.
"The results of this cohort study mean that for older people who aim to stay as functional as possible during advancing age, their blood pressure averaged out of the office, rather than in the office, might be the most important to target and treat," White said.
The American Academy of Family Physicians has more about cognitive decline.
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