Even a Small Drop in Blood Pressure May Help Protect Your Brain, Scans Reveal

Many people think of a blood pressure reading as news about their heart. Yet high blood pressure is also linked to changes in the brain, which can build for years before anyone notices.

Those changes have a name: cerebral small vessel disease. It affects tiny blood vessels and surrounding brain tissue, and is linked to stroke, cognitive decline, and dementia.

To see whether lowering blood pressure slows those brain changes, Sokratis neurologist Charisis of Massachusetts General Hospital, neuroimaging researcher Mohamad Habes of UT Health San Antonio, and colleagues compared brain scans taken about four years apart.

Their study found that MRI signs of small vessel disease progressed more slowly in people assigned a lower blood pressure target. Bigger drops in actual blood pressure were also associated with slower progression.

The researchers returned to SPRINT, a US clinical trial of more than 9,300 adults aged 50 and older with high blood pressure and increased cardiovascular risk.

Participants were randomly assigned a goal for the top number of their blood pressure reading, called systolic pressure: below 120 mmHg or below 140 mmHg.

The intervention began winding down in August 2015, ahead of schedule, after the lower-target group had fewer heart attacks, strokes, heart failure episodes, other acute coronary events, and cardiovascular deaths combined.

Deaths from all causes were also lower, according to SPRINT's original report.

Some participants had brain scans at the start and about four years later. A 2019 analysis found that white matter lesions grew less in the lower-target group.

These lesions appear as bright spots on MRI in tissue connecting brain regions. Other research covered by ScienceAlert has also examined links between high blood pressure, brain structure, and thinking skills.

But one marker can't show everything happening in small vessels.

"Small vessel disease affects the brain in several ways, and no single MRI marker captures the entire process," Habes told ScienceAlert.

This time, the team combined three MRI signs into one statistical score: white matter lesions near the brain's fluid-filled cavities, free-moving water in white matter, and visible spaces around tiny vessels deep in the brain. The score tracked how these signs changed together; it didn't count damaged vessels.

Of 663 participants with complete starting measurements, 442 had usable follow-up scans. Their average age was about 68, and a median of 3.9 years passed between scans.

By follow-up, average systolic pressure had fallen from about 136 to 120 mmHg in the lower-target group and from about 139 to 136 mmHg in the standard group.

Progression of the combined MRI score was 16.9 percent lower in the group assigned the below-120 target than in the below-140 group, relative to average disease burden at the start.

The researchers then asked whether actual blood pressure reductions were associated with different MRI outcomes. They compared each person's starting systolic pressure with the average of readings at visits at 6, 9, 12, 15, and 18 months.

Compared with participants whose pressure rose, those whose pressure fell by up to 10 mmHg had 21.2 percent less progression. The difference was 26.3 percent for drops of 10 to 20 mmHg and 39.4 percent for drops of at least 20 mmHg.

"The 39.4 percent means that participants whose systolic blood pressure fell by at least 20 mmHg had 39.4 percent less accumulation of small vessel disease burden, captured with our combined MRI measure, over time compared with participants whose blood pressure rose," Habes told ScienceAlert.

"It reflects slower accumulation of small vessel disease on MRI, not reversal of existing brain injury or disappearance of 39.4 percent of lesions."

The two results come from different comparisons. Participants were randomly assigned treatment targets, producing the 16.9 percent finding. They weren't assigned to achieve a particular blood pressure drop, so other differences could have contributed to the 39.4 percent finding.

"This analysis focused on MRI changes and did not establish that these participants experienced less cognitive decline or fewer strokes," Habes said.

Earlier research has linked greater small vessel disease burden with both outcomes.

The combined MRI score was analyzed after the original trial was designed, and many participants lacked usable follow-up scans. Additional analyses produced similar results.

This "reduces, but does not eliminate, this concern," Habes said.

SPRINT also excluded people with diabetes, prior stroke, dementia, symptomatic heart failure, or advanced kidney disease, as well as nursing home residents. Whether these findings apply to them remains uncertain.

Among those studied, assignment to the lower blood pressure target was associated with slower progression of MRI signs of small vessel disease.

The research has been published in eClinicalMedicine.