Nighttime Blood Pressure Measurement Can Identify High Risk Of Stroke

March 06, 1998

DALLAS, March 6 -- High blood pressure is already a primary risk factor for stroke, but Japanese researchers say that hypertensive patients who also exhibit a minimal nighttime dip in blood pressure may be at even higher risk, according to a study published in today's Stroke: Journal of the American Heart Association.

In their study of 105 individuals with high blood pressure, the researchers found that those who had high nighttime blood pressure and a minimal nighttime dip in blood pressure suffered the most severe brain damage when they had their stroke. Brain lesions occur when blood is cut off to part of the brain during stroke and the brain tissue dies. In lacunar strokes, which were studied extensively by the researchers, blood clots occur in the ends of small arteries, called arterioles, that penetrate deep into the brain.

In theory, blood pressure should be lower at night when people are resting. People normally have a "dip" in their blood pressure during the night. "Nondippers," those who don't have a nocturnal dip or only have a minimal dip, have been shown in other studies to have more severe cerebrovascular disease, say the researchers.

"These conclusions are interesting because they establish the danger of hypertension, which we all know very well, but also stress the importance of measuring nighttime blood pressure and what can happen if it is high, or does not dip," says the study's lead author Yasumasa Yamamoto, M.D., director of neurology at the Kyoto Second Red Cross Hospital in Kyoto, Japan. "Although multiple factors contribute to the development of new lesions, we can make a difference in the recurrence of stroke by controlling blood pressure more carefully."

The researchers used ambulatory blood pressure monitoring -- which examines blood pressure over a 24-hour period -- and magnetic resonance imaging (MRI) to determine how the patients' brain was damaged as a result of lacunar stroke. Lacunar stroke is often referred to as "silent" brain ischemia because it often does not exhibit symptoms and is sometimes not seen via traditional brain imaging. With the MRI, neurologists and neurosurgeons can get a better look at the tiny brain vessels that are blocked in lacunar strokes.

"Many studies have demonstrated that high blood pressure is strongly related to stroke occurrence," Yamamoto says. "Most were based on casual blood pressure readings. By using ambulatory blood pressure monitoring and MRI, we find that there is a stronger relation of blood pressure to the development of silent cerebrovascular lesions."

The patients were divided into five groups -- from those who showed no symptoms of stroke nor development of new brain lesions to patients who had more extensive cerebrovascular disease. Patients in groups 4 and 5 -- those who had silent lacunae or "white matter" lesions -- had nighttime systolic blood pressure readings that were significantly higher than the group who showed no symptoms. For example, patients with no symptoms had, on average, a nighttime blood pressure which was 10 points lower than their daytime blood pressure. In patients with the most severe damage, the "dip" was miniscule, ranging from 0.58 to 3.3 points lower.

This study demonstrated that a high ambulatory blood pressure, especially at night, and a reduced nocturnal blood pressure dip were both associated with the development of silent ischemic lesions and recurrent stroke in lacunar stroke patients. None of the patients showed the development of new lesions caused by excessive lowering of their daytime or nighttime blood pressure.

The scientists add that this is the first prospective study performed using ambulatory blood pressure monitoring and MRI.

Co-authors are Ihiro Akiguchi, M.D.; Kaiyo Oiwa, M.D.; Masamichi Hayashi, M.D.; Jun Kimura, M.D.

American Heart Association

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