What is 24-hour ambulatory blood pressure monitoring?
Twenty-four-hour ambulatory blood pressure monitoring is a way of measuring and managing high blood pressure (hypertension). Hypertension is a blood pressure measurement in which the systolic (upper) blood pressure is at or above 140 and the diastolic (lower) blood pressure is at or above 90.
Ambulatory blood pressure monitoring allows many blood pressure (BP) readings to be recorded over a 24-hour period, whether the patient is awake or asleep. At a doctor’s office or clinic, an instrument called a sphygmomanometer is used to take BP readings. Usually, only one or two readings are taken during a doctor’s visit. However, ambulatory BP monitoring yields many readings over a continuous period.
In most cases, with ambulatory BP monitors, readings are taken every 20 to 30 minutes during the day and every hour at night. The heart rate can also be measured at the same time.
Multiple BP readings can be averaged over the 24-hour period to obtain the mean or average BP. Variations in BP and heart rate, the BP distribution pattern, and other statistics can be calculated.
Why is 24-hour ambulatory blood pressure monitoring used?
Ambulatory BP monitoring provides additional information about how your changes in BP may correlate with your daily activities and sleep patterns. The United States Preventive Services Task Force (USPSTF) now recommends confirming a diagnosis of hypertension with ambulatory BP monitoring.
For most people systolic BP decreases about 10%-20% during sleep. However, for some people BP might not drop during sleep and may even rise.
Ambulatory BP monitoring can detect abnormal fluctuations in BP that might go unnoticed when BP is only measured in the doctor’s office. It is a very useful way to detect white coat hypertension, masked hypertension, and sustained hypertension:
- White coat hypertension: Some people who do not take BP lowering drugs (antihypertensive drugs) have elevated BP readings when their BP is taken at a doctor’s office or other health care setting. This is known as “white coat hypertension.” White coat hypertension can result in misdiagnosis of patients whose BP is actually normal. White coat hypertension has been observed in 15%-30% of patients with elevated BP readings. When ambulatory monitoring yields readings within the normal range outside the doctor’s office, patients usually do not need to take antihypertensive drugs.
- Masked hypertension: This condition occurs when a patient’s BP reading is normal at the doctor’s office, but is elevated when the patient is at home. It may occur in up to 20% of people who are being treated for hypertension.
- Sustained hypertension: This refers to BP readings that are elevated whether the patient is in the doctor’s office or at home. This condition has been linked to an increased likelihood of heart and kidney damage.