What is this?
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.
See also related separate article Hypertension.
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).
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 than office blood pressure measurement.
Who should be referred for ambulatory blood pressure monitoring?
- 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.
- 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.[6, 7]
- 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 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.
Downside to ambulatory blood pressure monitoring
- It is not universally 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.
- There is some evidence that HBPM may be better than ABPM for predicting cardiovascular risk at every level below severe hypertension (≥160/≥100 mm Hg). However, these findings need to be confirmed by larger trials.
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
- Blood pressure will fall at night in normotensive individuals. People who undergo this normal physiological change are described as 'dippers'.
- 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.
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- Haydar AA, Covic A, Jayawardene S, et al; Insights from ambulatory blood pressure monitoring: diagnosis of hypertension and diurnal blood pressure in renal transplant recipients. Transplantation. 2004 Mar 27 77(6):849-53.
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