Ambulatory Blood Pressure Monitor (ABPM)

Non-invasive ambulatory blood pressure monitoring (ABPM) is being increasingly used to assess patients with hypertension. This trend is supported by evidence that 24-hour blood pressure profiles may be superior to isolated clinic pressures. This is because a 24-hour reading is more reliable than a simple one-off reading. Patients often experience white coat hypertension (elevated BP in the presence of a doctor) and are wrongly diagnosed with high BP. Multiple readings are useful for evaluating the effectiveness of high BP treatments in patients who have commenced medication or other therapy. It is also a useful tool for monitoring BP in patients who feel weak or who are hypotensive.

• Ambulatory blood pressure (ABPM) may be a better predictor of cardiovascular events than clinic blood pressure readings.
• To exclude the possibility of white coat hypertension.
• Studies have shown that end-organ damage is more closely related to ambulatory blood pressure (ABPM) than clinic blood pressure readings.
• Patients with hypertension whose nocturnal blood pressure remains high, < 10% lower than the daytime average, may have a worse prognosis.
• ABPM provides a 24-hour profile, allowing assessment of clinic effects, drug effects, work influence, etc.

Most devices use either brachial artery microphones to detect Korotkoff sounds or cuff oscillometry where cuff pressure oscillations are detected. The measurement frequency can be varied, but it is usually between 20-30 minutes while awake and 30-60 minutes while sleeping. Patients can start or stop recordings and they can read the displayed results if they wish. Patient diaries are encouraged so that the cause of sudden changes in blood pressure can be evaluated. The units function poorly during strenuous activity and work best if the patient slows or stops moving.

• The small blood pressure cuff that is connected to the monitor will automatically check the blood pressure at regular intervals (about every 30 minutes), even while sleeping. A diary is given to record the day’s activities, so the doctor will know your active or resting state. The cuff can feel quite tight around the arm, but not painful.
• After 24 hours of monitoring, you will take the machine and your diary to the laboratory. The blood pressure information is transferred from the monitor to a computer. The doctor will then review the result and decide if your treatment program is working or if adjustments need to be done to your medicines.

The Upper limit of normal ambulatory blood pressure monitoring values

• Normal ambulatory blood pressure during the day is <135/<85 mm Hg and <120/<70 mm Hg at night.
• Levels above 140/90 mm Hg during the day and 125/75 mm Hg at night should be considered as abnormal.

• This varies according to the machines used.
• Usually, they have individual systolic and diastolic pressures. These may also be represented in a graphic form.

A nurse will fit the monitor and explain the whole procedure. This takes approximately 10-15 minutes. No special preparations are necessary for the test, but it is sensible to wear a blouse or shirt that is loose on the arms or a short-sleeved/sleeveless shirt.

You will be asked to fill out a diary indicating your activities over the 24 hour period so that BP changes can be linked with exercise. Removing the monitor the next day takes only a few minutes. Do not shower or bathe while wearing the unit.