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Obtaining a blood pressure profile

Accurate though measurement may be when the above recommendations are followed, any such measurement represents only a fraction of the 24 h blood pressure profile. The increasing use of 24 h ambulatory blood pressure measurement in clinical practice has shown several patterns of blood pressure behaviour, such as the "white coat" effect whereby the circumstances of measurement may in themselves induce a rise in blood pressure. It is therefore important to attempt to obtain a profile of blood pressure behaviour. This can be best achieved by 24 h ambulatory measurement, but repeated measurements of blood pressure at successive visits also give helpful information on blood pressure behaviour.

Careful measurement of blood pressure with a mercury sphygmomanometer following the above recommendations is likely to remain the most effective first line in assessing blood pressure. If the blood pressure by conventional measurement is above 150/90 mm Hg, especially over several measurements, an assessment of blood pressure behaviour should be obtained before diagnostic and therapeutic decisions are made.

Self (home) measurement

Blood pressure measured in the home is usually lower than that recorded by a doctor or nurse in a clinical setting. Home measurement of blood pressure has failed to achieve the success and popularity of home blood sugar measurement by patients with diabetes, mainly because of the inaccuracy of blood pressure measuring devices. The advent of accurate and inexpensive automated devices that can provide a print-out of blood pressure measurement with time and date should remove many of the drawbacks and lead to increased attention to home blood pressure measurement.

Ambulatory blood pressure measurement (ABPM)

The increased demand for 24 h blood pressure measurement has resulted in the production of a variety of ambulatory devices. Ambulatory systems must be accurate and reasonably priced and the recorders should be compact, noiseless, and light and comfortable for the patient to wear. In obese patients a cuff containing an appropriately sized bladder must be used.

  • The operator must:
    • be familiar with the equipment
    • know the calibration procedures for the device
    • know the normal ranges of blood pressure during the day and night
    • be aware of the factors influencing the diurnal pattern
    • give the necessary time to instruct the subject so as to obtain as many measurements as possible during the recording period.
  • Subjects for ABPM must be capable of coping with and caring for the recorder.
  • Normal activity should be maintained during ABPM except when measurements are being made by the recorder.
  • The subject's arm should be still during measurement.
  • The subject's levels of activity should be similar for comparative repeat measurements.
  • Working days should not be compared with recreational days.
  • Compare measurements in shift workers between similar shifts.
  • For clinical use recordings are usually programmed for every 30 min.
  • Subjects should keep a diary of activities and symptoms during the recording period.

The clinical indications for ABPM are growing. In addition to miscellaneous diagnostic uses, it is used mainly to assess and evaluate:

"White coat hypertension"

White coat hypertension can be defined simply as a rise in blood pressure associated with the procedure of having blood pressure measured. It may result partly from anxiety but in many subjects there is a deeper "learning" process that may condition the rise in blood pressure for the procedure of measurement. Whatever the mechanism, the reality is that as many as 10-20% of patients labelled as having "hypertension" using conventional blood pressure measurement may have "white coat hypertension" and may not require blood pressure lowering drugs. ABPM is the most effective method of determining whether blood pressure elevation is the result of "white coat hypertension".

"White coat effect"

The white coat effect can be defined as a rise in blood pressure in patients with hypertension associated with the procedure of having blood pressure measured. It occurs in many hypertensive patients and its clinical importance is that patients with hypertension may appear more hypertensive than is the case if ABPM is used to assess blood pressure elevation.

 

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BHS 1999