Clinical value of ambulatory blood pressure monitoring

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Abstract
Ambulatory blood pressure monitoring (ABPM) has now become an established clinical tool. It is appropriate to take stock and assess the situation of this technique. Important improvements in equipment have occurred, with reductions in weight, in awkwardness and in noisiness of the machines, better acceptability and tolerance by the patients, and better reliability. Validation programmes have been proposed and should be referred to. Limitations of the technique persist with intermittent recording in current practice. The reproducibility is limited in the short-term while recording over 24 h is acceptable. White-coat effect (WCE) is manifested as a transient elevation in blood pressure during the medical visit. The frequency of this phenomenon, the size of the effect, age, sex and level of blood pressure (BP) or the situation of occurrence (general practitioner, specialist or nurse) have been interpreted differently. It does not seem that WCE predicts cardiovascular morbidity or mortality. White-coat hypertension (WCH) is diagnosed on the evidence of abnormal clinical measures of BP and normal ABPM. The latest upper limits of normality by ABPM recommended by the JNCVI are < 135/85 mmHg while patients are awake and < 120/75 mmHg while patients are asleep. If we accept these upper limits of normality in ABPM, WCH does not appear to be a real problem as regards risk factors or end-organ effects. In terms of prognosis, data are limited. Cardiovascular morbidity seems low in WCH but identical to that of hypertensive subjects in these studies. However, further studies are needed to confirm these results. WCH does not appear to benefit from anti-hypertensive treatment. It is obvious that the lower the BP regarded as the limit of normality, the less likely the occurrence of secondary effects of metabolism, or end-organ effects or complications in those classified as hypertensive. One of the most specific characteristics of ABPM is the possibility of being able to discover modification or alteration of the 24 h cycle of BP. Non-dippers are classically defined as those who show a reduction in BP of less than 10/5 mmHg or 10% between the day (06.00–22.00 h) and the night, or an elevation in BP. In contrast, extreme dippers are those in whom the BP reduction is greater than 20%. The data remain inconclusive with regard to the existence of a consistent relationship between the lack of a nocturnal dip in blood pressure and target organ damage. As regards prognosis, it seems that an inversion of the day–night cycle is of pejorative significance. Almost all studies have shown that non-dippers had a significantly higher frequency of stroke than dippers. In contrast, too great a fall in nocturnal BP may be responsible for more marked cerebral ischaemia. Non-dippers have a significantly elevated median urinary excretion of albumin. There is a significant correlation between the systolic BP and nocturnal diastolic BP, and urinary excretion of albumin. Various studies have confirmed the increased frequency of change in the 24 h cycle in hypertensive subjects at the stage of renal failure. BP abnormalities should be considered as markers of an elevated risk in diabetic subjects but cannot be considered at present as predictive of the appearance of micro-albuminuria or other abnormalities. ABPM is thus of interest in type I or type II diabetes both in the initial assessment and in the follow-up and adaptation of treatment. The introduction of ABPM has truly changed the means and possibilities of approach to the study of the effects of anti-hypertensive medications, with new possibilities of analysis such as trough–peak ratio smoothness index, etc.