24-hour ambulatory blood pressure monitoring is a method for continuously measuring blood pressure. Your BP is measured even while you sleep. Ongoing data helps your doctor get a more accurate picture of your blood pressure numbers.
What is 24-hour ambulatory blood pressure monitoring?
Twenty-four-hour ambulatory blood pressure monitoring is a way to measure and manage high blood pressure (hypertension).
Hypertension is a blood pressure measurement where your systolic (upper) blood pressure is 130 or higher and your diastolic (low) blood pressure is 80 (or 130/80) or higher. Ambulatory blood pressure monitoring allows your blood pressure (BP) readings to be recorded over a 24-hour period whether you are awake or asleep.
While at your doctor’s office or clinic, an instrument called a sphygmomanometer is used to take your blood pressure readings. Usually, only one or two readings are taken during your visit.
Ambulatory BP monitoring provides many readings over a continuous period of time. In most cases, readings are taken every 20 to 30 minutes during the day and every hour at night. Your heart rate can be measured at the same time. These multiple readings are averaged over a 24-hour period. Changes in BP and heart rate, BP distribution pattern, and other statistics are calculated.
Why use 24-hour ambulatory blood pressure monitoring?
Ambulatory BP monitoring provides additional information about how changes in your BP may relate to your daily activities and sleep patterns. The blood pressure management guidelines of the American Heart Association and the American College of Cardiology now strongly recommend confirming the diagnosis of hypertension with ambulatory BP monitoring.
For most people, systolic blood pressure decreases by about 10% to 20% during sleep. However, for some people, blood pressure may not drop during sleep. It may even rise.
Ambulatory BP monitoring can detect abnormal changes in BP that may not be noticed when measured only in the doctor’s office. It is a useful way to detect white coat hypertension, masked hypertension, and persistent hypertension.
- Whitecoat hypertension: Some people who are not taking blood pressure-lowering drugs (antihypertensive drugs) have high readings of blood pressure when taken in a healthcare setting. This is known as “white coat hypertension”. Whitecoat hypertension can result in misclassification of patients whose blood pressure is indeed normal. Whitecoat hypertension has been seen in 10% to 30% of patients with high BP readings. Current guidelines do not recommend treatment when outpatient monitoring shows readings in the normal range outside the doctor’s office. However, ongoing research suggests that this may still indicate a blood pressure problem, so you and your provider should be mindful of this.
- Masked hypertension: This condition occurs when your BP reading is normal at the doctor’s office but elevated when you are at home. It can be seen in up to 20% of untreated people. This condition carries a similar risk to persistent hypertension and should be treated with antihypertensive drugs.
- Persistent hypertension: This refers to rising BP readings whether you are at the doctor’s office or at home. This condition has been associated with an increased chance of heart and kidney damage.
Are there other uses for 24-hour ambulatory blood pressure monitoring?
Ambulatory blood pressure monitoring is increasingly used to determine how well certain antihypertensive drugs can control high blood pressure. In some cases, antihypertensive drugs cannot effectively control blood pressure all day and night. A doctor may need to adjust the prescribed dose or the amount of time the drug is given, depending on the patient’s blood pressure patterns. In other cases, more than one drug may be required to stabilize BP.
Outpatient blood pressure monitoring can also help predict the likelihood of cardiovascular (blood vessels in the heart) and cerebrovascular (blood vessels in the brain) disease due to hypertension and organ damage.
Ambulatory BP monitoring may also be appropriate in other situations, such as:
- Pregnant women with hypertension.
- People with “borderline” hypertension.
- Difficulty controlling BP with medication.
- BP varies depending on other drugs.
- Changes in prescription drugs that may affect BP.
- Fainting attacks or hypotension (low BP).
What are the benefits of 24-hour ambulatory blood pressure monitoring?
Outpatient monitoring can rule out white coat hypertension so that people are not given unnecessary prescriptions for BP-lowering drugs. It can also detect masked hypertension so people take necessary medications for high blood pressure. Among these patients, the incidence of stroke, heart disease, and hypertension-related organ damage may be reduced. Outpatient monitoring can also be useful in assessing a patient’s response to long-acting antihypertensive drugs.
What are the disadvantages of 24-hour blood pressure monitoring?
You may experience some discomfort due to 24-hour BP monitoring. The pressure from repeated inflation of the cuff can cause pain in your upper arm. BP readings during the night can affect your sleep. The cuff can also irritate the skin and cause a mild rash on the arm that usually goes away on its own. Some insurance companies do not reimburse patients who use outpatient devices unless white coat hypertension or masked hypertension is suspected.
How are 24-hour ambulatory blood pressure readings taken?
BP readings are taken continuously over a 24-hour period. You will install a device that is approximately the same size as a portable radio. The device is attached to a belt or strap that is worn around your body. It collects information over a 24-hour period, which is then transferred to a computer.
You will wear a BP cuff attached to the device around your upper arm. (The cuff can be worn under the clothes so that it is not visible.) The cuff inflates at regular intervals during the day and night. You may be asked to keep a diary to record your daily readings. This can help show how changes in your BP relate to periods of activity or rest.
After 24 hours, you can remove the device and BP cuff and return the equipment to your clinic or doctor’s office. A computer analyzes the readings and produces results.
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- Turner JR, Viera AJ, Shimbo D. Ambulatory blood pressure monitoring in clinical practice: a review. (https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4877527/) Am J Med. 2015;128(1):14-20. Accessed 11/8/2021.
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