What is this?
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).
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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.
Further reading & references
- White WB; Importance of aggressive blood pressure lowering when it may matter most. Am J Cardiol. 2007 Aug 6;100(3A):10J-16J. Epub 2007 May 25.
- Wexler R; Ambulatory blood pressure monitoring in primary care. South Med J. 2010 May;103(5):447-52.
- Clement DL, De Buyzere ML, De Bacquer DA, et al; Prognostic value of ambulatory blood-pressure recordings in patients with treated hypertension. N Engl J Med. 2003 Jun 12;348(24):2407-15.
- McGrath BP; Ambulatory blood pressure monitoring. Med J Aust. 2002 Jun 17;176(12):588-92.
- Mancia G, Parati G; Office compared with ambulatory blood pressure in assessing response to antihypertensive treatment: a meta-analysis. J Hypertens. 2004 Mar;22(3):435-45.
- Ernst ME, Bergus GR; Ambulatory blood pressure monitoring. South Med J. 2003 Jun;96(6):563-8.
- 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.
- Fagard RH, Staessen JA, Thijs L, et al; Relationship between ambulatory blood pressure and follow-up clinic blood pressure in elderly patients with systolic hypertension. J Hypertens. 2004 Jan;22(1):81-7.
- O'Brien E, Beevers G, Lip GY; O'Brien E, Beevers G, Lip GY; ABC of hypertension: Blood pressure measurement. Part IV-automated sphygmomanometry: self blood pressure measurement. BMJ. 2001 May 12;322(7295):1167-70.
|Original Author: Dr Gurvinder Rull||Current Version: Dr Gurvinder Rull|
|Last Checked: 25/08/2010||Document ID: 1792 Version: 21||© EMIS|
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