Ambulatory blood pressure monitoring

What is ambulatory blood pressure monitoring?

Ambulatory blood pressure monitoring (ABPM) is a non-invasive method of obtaining blood pressure readings over a 24-hour period, whilst the patient is in their own environment, representing a true reflection of their blood pressure.

Many studies have now confirmed that blood pressure measured over a 24-hour period is superior to clinic blood pressure in predicting future cardiovascular events and target organ damage.¹

See also the related separate Hypertension article.

What does ambulatory blood pressure monitoring involve?

Blood pressure is measured over a 24-hour period, using auscultatory or oscillometry devices, and requires use of a cuff. The monitor takes blood pressures every 20 minutes (less frequently overnight - eg, one-hourly).²

What are the uses of ambulatory blood pressure monitoring?³

• To obtain a twenty-four hour record - more reliable than one-off measurements. Studies have shown that increased blood pressure readings on ABPM are more strongly correlated to end-organ damage than one-off measurements - eg, left ventricular hypertrophy.⁴

• To detect white coat hypertension.

• It has use in hypertension research - eg, reviewing 24-hour profile of antihypertensive medication.

• It may have prognostic use - higher readings on ABPM are associated with increased mortality.⁵

• Response to treatment.⁴

• Masked hypertension.

• Episodic dysfunction.

• Autonomic dysfunction.

• Hypotensive symptoms whilst on antihypertensive medications.

• It may be more cost-effective in the long term than office blood pressure measurement.

Who should be referred for ambulatory blood pressure monitoring?⁶

• The National Institute for Health and Care Excellence (NICE) recommends that if a clinic blood pressure is 140/90 mm Hg or higher, ABPM should be offered to confirm the diagnosis of hypertension. If a person is unable to tolerate ABPM, home blood pressure monitoring (HBPM) is a suitable alternative to confirm the diagnosis of hypertension.⁷

• Poorly controlled hypertension - eg, suspected drug resistance.

• Patients who have developed target organ damage despite control of blood pressure.

• Patients who develop hypertension during pregnancy.

• High-risk patients - eg, those with diabetes mellitus, those with cerebrovascular disease, and kidney transplant recipients.

• Suspicion of white coat hypertension - high blood pressure readings in clinic which are normal at home.

• Suspicion of reversed white coat hypertension, ie blood pressure readings are normal in clinic but raised in the patient's own environment.

• Postural hypotension.

• Elderly patients with systolic hypertension.

Upper limit of normal ambulatory blood pressure monitoring values

Normal ambulatory blood pressure during the day is <135/<85 mm Hg.⁷

Disadvantages of ambulatory blood pressure monitoring³

• It is not universally available although this is improving.

• It requires specialist training and is not common in the USA.⁸

• Some patients find inflation of the cuff unbearable.

• Sleep disturbance.

• Bruising might be seen where the cuff is located.

• Background noise may lead to interference (less with oscillometric methods).

• Poor technique and arrhythmias may cause poor readings.

• HBPM may be better than ABPM for monitoring response to treatment.²

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.⁷

Dippers and non-dippers

• Blood pressure will fall at night in normotensive individuals. People who undergo this normal physiological change are described as 'dippers'.⁹

• In 'non-dippers' the blood pressure remains high, ie less than 10% lower than daytime average. There is also the phenomenon of 'reverse dippers' whose blood pressure actually rises at night. Both these conditions have also been reported to be associated with a poor outcome.¹⁰