A widely used test for measuring nighttime blood pressure may interfere with patients' sleep, thus affecting the results of the test, reports a study in an upcoming issue of Clinical Journal of the American Society of Nephrology (CJASN).
"Blood pressure (BP), measured during sleep correlates better with heart attacks and strokes compared to blood pressure measured in the doctor's office," explains Rajiv Agarwal, MD (Indiana University and Veterans Affairs Medical Center, Indianapolis). "However, if blood pressure measurement disturbs sleep, then it may weaken the relationship between 'sleeping BP' and these cardiovascular events."
Along with his data-manager, Robert Light, BS (also of Indiana University), Agarwal analyzed the results of 24-hour blood pressure monitoring in 103 patients with kidney disease. This ambulatory blood pressure monitoring test is commonly performed to assess variations in blood pressure from daytime to nighttime. Blood pressure normally "dips" at night—when it doesn't, the cardiovascular risks of high blood pressure are much greater. As part of a research study, the patients' activity levels were measured using a wristwatch-like device called an actiwatch.
"We were measuring activity, sleep and ambulatory BP for diagnosing masked hypertension and found this interesting observation," explains Dr. Agarwal. The lack of the normal nighttime 'dip' in blood pressure was related to increased activity levels, because the blood pressure monitor was disturbing the patients' sleep. On nights when patients were using the blood pressure monitor, they spent an average of 90 minutes less time in bed. They also spent less time asleep and slept less efficiently.