Ambulatory blood pressure monitoring (ABPM) is a noninvasive method of obtaining blood pressure readings over twenty-four hours, 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.
What does ambulatory blood pressure monitoring involve?
Blood pressure is measured over twenty-four hours using auscultatory or oscillometry and requires use of a cuff. The monitor takes blood pressures every 20 minutes (less frequently overnight, eg 1-hourly).
What are the uses of ambulatory blood pressure monitoring?
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.
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.
- Response to treatment.
- Masked hypertension.
- Episodic dysfunction.
- Autonomic dysfunction.
- Hypotensive symptoms whilst on antihypertensive medications.
- It may be more cost-effective in the long-term.
- Who should be referred for ambulatory blood pressure monitoring?
Any patient with persistently raised blood pressure readings or labile blood pressure should be considered for ABPM (whether or not on treatment). However, it is not a screening tool.
- Borderline readings in clinic.
- 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 renal 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 BP during the day is <135/<85 and <120/<70 at night.
- Levels above 140/90 during the day, and 125/75 at night should be considered as abnormal.
- Downside to ambulatory blood pressure monitoring
- It is not widely available although this is improving.
- It requires specialist training.
- Some patients find inflation of the cuff unbearable.
- Sleep disturbance.
- Bruising where the cuff is located.
- Background noise may lead to interference (less with oscillometric methods).
- Poor technique and arrhythmias may cause poor readings.
- How are the results of ambulatory blood pressure monitoring provided?
- This varies according to the machines used.
- Night-time mean, daytime mean and overall mean are also provided.
- 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.
- There are lots of other analyses that are possible - they have varied uses.
Day and night blood pressure: there is some evidence that night-time blood pressure gives crucial information, such as higher night-time readings being more associated with risk of developing target end-organ damage.
Dippers and non-dippers
Blood pressure will fall at night in normotensive individuals.
In hypertensive patients the blood pressure may fall excessively at night (>10%), leading to describing patients as 'dippers', which is associated with a poor outcome.
In 'non-dippers' the blood pressure remains high, ie less than 10% lower than daytime average. This has also been reported to be associated with a poor outcome