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Ambulatory Blood Pressure Monitoring

What is this? Ambulatory Blood Pressure Monitoring (ABPM) is a non-invasive 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.

What does ABPM 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 over night).

What are the uses of ABPM?

1. Get 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 hypertrophy1, 2.
2. Avoid white coat hypertension.
3. Use in hypertension research e.g. reviewing 24 hour profile of anti-hypertensive medication.
4. May have prognostic use - higher readings on ABPM are associated with increased mortality (see below). For example, higher readings on ABPM are associated with increased cardiovascular mortality3.
5. Reproducible and reliable.
6. May be more cost effective in the long-term.

Who should be referred for ABPM?

1. 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 tool4.
2. Borderline readings in clinic.
3. Poorly controlled hypertension e.g. suspect drug resistance.
4. Patients who have developed target organ damage despite control of blood pressure.
5. Patients who develop hypertension during pregnancy.
6. High risk patients e.g. diabetes mellitus, cerebrovascular disease and renal transplant recipients 5, 6.
7. Suspicious of white coat hypertension - high blood pressure readings in clinic which are normal at home.
8. Suspicious of reversed white coat hypertension - i.e. blood pressure readings are normal in clinic but raised in patients own environment.
9. Postural hypotension.
10. Elderly patients with systolic hypertension7.

Downside to ABPM?

• Not widely available.
• 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 readings8.

How are the results of ABPM provided?

• This varies according to the machines used.
• Usually have average systolic and diastolic pressures.
• Night time means and day means are also summarised.
• 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 are more associated with risk of developing target end-organ damage.

In hypertensive patients the blood pressure may fall at night - leading to describing patients as dippers and non-dippers1, 4, 5.

• In "dippers" the blood pressure falls > 10% at night, compared with the average daytime readings. (Thought to be normal).
• In "non-dippers" the blood pressure remains high - i.e. less than 10 % lower than daytime average. This has been reported to be associated with a poorer outcome.

References Used

1. McGrath BP; Ambulatory blood pressure monitoring.;Med J Aust. 2002 Jun 17;176(12):588-92.[abstract]
2. 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]
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. Mallion, J-M., Baguet, J-P. and Mancia, G. (2005) Clinical Value of Ambulatory Blood Pressure Monitoring, European Society of Hypertension Scientific Newsletter, 6, Number 19. {As PDF]
5. Ernst ME, Bergus GR; Ambulatory blood pressure monitoring.;South Med J. 2003 Jun;96(6):563-8.[abstract]
6. 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]
7. 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]
8. 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 EMIS is grateful to Dr Gurvider Rull for rewriting this article. The final copy has passed peer review of the independent Mentor GP authoring team. ©EMIS 2006.

Last issued 05 Jul 2006