Ambulatory blood pressure is accomplished with a special device that consists of a blood pressure cuff that is worn on your arm, and is attached to a small recording device that you wear on your belt. You wear the ABP device for either 24 or 48 hours, and it records your blood pressure periodically (usually at 15-minute or 30-minute intervals) throughout that period, during your routine daily activities and while you are sleeping.
So the ABP provides your doctor with a complete record of your blood pressure for a one- or two-day period.
The information the ABP provides is fundamentally different from the information the doctor gets by taking your blood pressure in the office. The office blood pressure recording is a single value that is meant to reflect your blood pressure during quiet rest (which explains why, given the hectic environment of most doctors offices these days, the readings may not always be entirely accurate).
ABP, in contrast, reports your blood pressures as they are obtained through a wide range of situations and activities — from running to catch a bus to sleeping. And it is normal for a person’s blood pressure to fluctuate tremendously during the many activities a person typically performs in a day. So, unlike the blood pressure you get in the doctor’s office, the ABP does not report merely a single value for systolic and diastolic blood pressure that supposedly represents your official “blood pressure.” Instead, it reports an entire range of (often) widely variable values throughout the course of a day or longer.