INTRODUCTION

Ambulatory Blood Pressure Monitoring (ABPM) is when your blood pressure is being measured as you move around, living your normal daily life. It is normally carried over 24 hours. It uses a small digital blood pressure machine that is attached to a belt around your body and which is connected to a cuff around your upper arm. It small enough that you can go about your normal daily life and even sleep with it on.

BACKGROUND

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 Dzwhite coatdz 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.

Why use ambulatory blood pressure monitoring?

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

How they work

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.

What happens during the 24-hour ABPM?

  • 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 ifyour treatment program is working or if adjustments need to be done in your medicines.

What is a “normal” 24 hour blood pressure?

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.

How are the results of ambulatory blood pressure monitoring provided?

  • This varies according to the machines used.
  • Usually, they have individual systolic and diastolic pressures. These may also be represented in a graphic form.
  • Blood pressure load – the percentage or proportion of readings that are higher than a predetermined level in twenty-four hours.
  • NICE recommends ensuring that at least two measurements per hour are taken during the person’s usual waking hours (for example, between 08:00 and 22:00 hours). Use the average value of at least 14 measurements taken during the person’s usual waking hours to confirm a diagnosis of hypertension.

Dippers and non-dippers

  • Most people, including the majority of patients with hypertension, have a lower blood pressure while asleep (dippers).
  • The systolic and diastolic falls in hypertensive patients are usually 10-15%, but do not fall to normal levels. However, in 30% of hypertensive patients, the nocturnal fall is smaller than usual, may not occur, or the pressure may even rise.
  • It may be important to identify this group of ‘non-dippers’ because, from preliminary data, they appear to have a worse prognosis. This can be measured as cardiovascular morbidity and mortality as well as increased end organ damage including left ventricular hypertrophy.
  • ABPM is the simplest way to detect ‘non-dippers’. As a group, they appear to have more severe or complicated forms of hypertension and are often older.

PRE/POST PROCEDURE

What are the preparations for the 24-hour ABPM and how long does it take?

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.

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