Ambulatory blood pressure monitoring: methodologic issues

Blood pressure, like heart rate, is a changing physiologic variable. Like ambulatory electrocardiography, ambulatory blood pressure can be recorded intermittently throughout the day. Ambulatory blood pressure is a dynamic variable influenced by multiple factors, and it correlates more strongly with target organ damage than do static office blood pressure measurements. Office (but not ambulatory) measurements are subject to the placebo and physician pressor effect. There is a great patient variability of blood pressure measurements in the office compared with ambulatory methods. Ambulatory blood pressure devices are portable rather than 'ambulatory'. The auscultatory (listens for Korotkoff sounds) and oscillometric (detects maximal arterial vibrations and calculates diastolic blood pressure) methods are used to detect blood pressure. Equipment is generally safe, although mild sleep derangements have been reported. The 24-h blood pressure and diurnal change are usually assessed. A 24-h ambulatory blood pressure mean of 140/90 mm Hg or above is clearly abnormal, though recent data suggest that the 95th centile is 134/84 mm Hg. Correlation of individual blood pressure readings with diary entries may be instructive. New American and British validation criteria have been published to assess the performance of each new device that becomes available. It should not be assumed that newer ambulatory devices have been tested (particularly by a third party) or are better. Test/retest 24-h ambulatory blood pressure shows less variability than office measurements; however, the percentage of patients with a mean difference greater than +/- 5 mm Hg on repeat 24-h blood pressure measurement after 1 week is still surprisingly high (49.3%, systolic; 52.1%, diastolic). European trials are in progress to assess the prognosis of hypertension assessed by ambulatory compared with office blood pressure. Ambulatory blood pressure monitoring has been restricted for use in several clinical situations and is not used for the routine evaluation and management of hypertension.