January 7, 2010

Aging and HIV Independently Affect Blood Flow to Brain

Both aging and HIV independently affect blood flow to the brain, but the two together don’t have an additive effect, according to a study published online January 4 in The Journal of Infectious Diseases.

Rates of brain damage were once considerable in people with advanced HIV disease, particularly AIDS dementia complex. Though the reason(s) for brain damage in people living with HIV has not been fully explained, two possible factors have been described: a direct effect of HIV or the immune response in the brain, or decreased blood flow to the brain because of HIV’s effect on the cardiovascular system.

Powerful combination antiretroviral (ARV) treatment, introduced in 1996, not only cut the death rate in people with HIV, but also significantly reduced the incidence of many of these brain-related illnesses over time. As people are now living longer, however, there are more concerns about decline in brain function as people age into their 50s and 60s.

To determine the affect of both aging and HIV on brain function, Beau Ances, MD, PhD, from the Department of Neurology at Washington University in St. Louis, and his colleagues conducted functional magnetic resonance imaging (fMRI) on 26 HIV-positive and 25 HIV-negative people. While fMRI can’t measure the exact functioning of different parts of the brain, it does detect the amount of blood flow to various brain areas. Scientists have been able to extrapolate how blood flow, or lack of it, affects brain and motor function.

The average age in both groups was about 40, and more than half were male. The average CD4 count of the HIV-positive group was 486, and 60 percent were taking ARV treatment.

It turned out that age, in both groups, was associated with a decline in cerebral blood flow. With each 15 year increase in age, there was a 22 percent reduction in blood flow.  HIV infection was also associated with a roughly 22 percent reduction in blood flow.  

There was no synergistic effect of age and HIV status, however. If there were an interaction, for instance, a 55-year-old HIV-positive person would have greater than a 22 percent reduction in cerebral blood flow compared with a 55-year-old HIV-negative person—but this was not the case.

The authors aren’t recommending people with HIV routinely undergo fMRI tests of brain function. They do, however, indicate fMRI could be a useful tool to further study HIV’s impact on the brain.

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