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.^1,2

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, e.g. 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, e.g. left ventricular hypertrophy.^3,4
• To detect white coat hypertension.
• It has use in hypertension research, e.g. 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.²
• Masked hypertension.²
• Episodic dysfunction.²
• Autonomic dysfunction.²
• Hypotensive symptoms whilst on antihypertensive medications.²
• 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, e.g. suspected drug resistance.
• Patients who have developed target organ damage despite control of blood pressure.
• Patients who develop hypertension during pregnancy.
• High-risk patients, e.g. those with diabetes mellitus, those with cerebrovascular disease and renal 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, i.e. blood pressure readings are normal in clinic but raised in the patient's own environment.
• Postural hypotension.
• Elderly patients with systolic hypertension.⁸

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.²

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.⁹

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.^3,6
• In 'non-dippers' the blood pressure remains high, i.e. less than 10% lower than daytime average. This has also been reported to be associated with a poor outcome.

Document references

1. 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. [abstract]
2. Wexler R; Ambulatory blood pressure monitoring in primary care. South Med J. 2010 May;103(5):447-52. [abstract]
3. 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. [abstract]
4. McGrath BP; Ambulatory blood pressure monitoring. Med J Aust. 2002 Jun 17;176(12):588-92. [abstract]
5. 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. [abstract]
6. Ernst ME, Bergus GR; Ambulatory blood pressure monitoring. South Med J. 2003 Jun;96(6):563-8. [abstract]
7. 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. [abstract]
8. 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. [abstract]
9. 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.

Acknowledgements