The 24-hour ambulatory blood pressure monitoring may interfere with patients’ sleep, thus affecting the results of the test, according to a study in Clinical Journal of the American Society of Nephrology.

"Blood pressure (BP), measured during sleep, correlates better with heart attacks and strokes compared to blood pressure measured in the doctor’s office," said 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."

Agarwal and his data-manager, Robert Light, BS, analyzed the results of 24-hour blood pressure monitoring in 103 patients with kidney disease. This monitoring test is commonly performed to assess variations in blood pressure from daytime to nighttime. Each study participant also wore an actigraph to monitor activity levels.

A lack of the normal nighttime “dip” in blood pressure was related to increased activity levels, because the monitor was disturbing the patients’ sleep. On nights when patients were using the blood pressure monitor, they spent an average of 90 minutes less in bed. The study participants also spent less time asleep and slept less efficiently.

"We were measuring activity, sleep, and ambulatory BP for diagnosing masked hypertension and found this interesting observation," said Agarwal.

Patients who awoke at night during blood pressure monitoring were 10 times less likely to have the normal nighttime dip in BP.

"Nighttime blood pressure is lower not because of the time of the day, but because people are asleep," said Agarwal. "The ambulatory monitoring technique can disturb sleep, and therefore raise the nighttime blood pressure as an artifact.”

Agarwal emphasized that sleep quality should be taken into account when interpreting blood pressure during sleep.