The Importance of Ambulatory Blood Pressure Monitoring

Part 1 of 2: Defining Blood Pressure, Office and Home Blood Pressure Measurement.

In order to understand the importance of ambulatory blood pressure monitoring, one first needs to understand why blood pressure is important to measure. While hypertension specialists understand the value of ambulatory blood pressure monitoring, some family practice physicians don't understand the utility of ABPM over home blood pressure monitoring. Let's start with the basics....

What is blood pressure?
Blood pressure measurements are typically displayed as a ratio, such as 120/80. Systolic BP (the top number in the ratio) is the peak pressure in the arteries when the heart pumps, while diastolic BP (the bottom number in the ratio) is the minimum pressure in the arteries when the heart relaxes between beats. The well-known standard for blood pressure is keeping it below 140/90.[1]

Why is having my blood pressure measured important?
Cardiovascular disease (CVD) is responsible for one-third of global deaths, and high blood pressure is a contributing risk factor in both CVD and stroke.[2] Hypertension in industrialized countries is not a new problem, and it's now becoming more prevalent in developing areas of the world. One in three US adults has high blood pressure and of those US adults with hypertension, only 45% have it in control. Let me emphasize this point: of the substantial percentage of the US population with diagnosed hypertension, over half do not have their blood pressure within a normal range. The estimated cost of high blood pressure in the US for 2009 is $73.4 billion [3]; it is an expensive problem, but it is preventable!

How can I measure my blood pressure?
There are three types of blood pressure measurement: physician's office BP, home BP, and ambulatory BP. It's important to understand the differences between the types of blood pressure measurement techniques to understand what is best suited for you.

Office blood pressure measurement
Every time you visit the doctor, your blood pressure should be measured. It's typically measured at the beginning of the visit after you've been sitting in the waiting room and you are called in to get your vital signs measured (weight, height, temperature). This is office blood pressure measurement. Your blood pressure varies throughout the day as your activities, mood, and stress level vary, so this single blood pressure reading does not tell the whole story. Do you think your blood pressure is the same while you're driving in rush hour traffic as it is when you are relaxing at home? It's not! Home blood pressure measurement and ambulatory blood pressure measurement give your physician much more information than BP readings at a single office visit.

Home blood pressure measurement
Inexpensive home BP monitors are widely available at pharmacies, which has made patient monitoring of blood pressure outside of the clinic more prevalent. This easy access to home BP measurements has improved patient awareness in health and treatment. Home BP monitors also provide a better understanding of how blood pressure changes throughout the day, providing the physician with more information than that which can be measured in the doctor's office.

While there are several advantages to home BP measurement, there are a few drawbacks including: accuracy, consistency, and cuff size. Home BP monitors are not clinical grade, so they are not held to the same standards of accuracy as those devices in your physician's office. Home BP is also demanding of patients because in order for it to provide valuable data, patients must be diligent in measuring and recording data consistently (same time of day, etc). Most problematic is that home BP monitors typically offer only one cuff, and with a quick search, a standard cuff size accompanying a home BP monitor is 22-33cm. Recent NHANES data shows that the average American adult arm circumference is 32cm, meaning the cuff with the home BP monitor is too small for half of adult Americans. When blood pressure cuffs are too small, the blood pressure monitor will give readings that are too high and inaccurate. While these devices can be good for identifying blood pressure trends, there are obviously some drawbacks to simply relying on home BP measurements.

[1] http://familydoctor.org/online/famdocen/home/common/heartdisease/treatment/770.html

[2] World Health Organization. (2003). 2003 World Health Organization (WHO)/ International Society of Hypertension (ISH) statement on the management of hypertension. Journal of Hypertension, 21, 1983-1992.

[3] American Heart Association Statistics Committee and Stroke Statistics Committee. (2009). Circulation, 119, e21 - e181.