Predictive value of blood pressure dipping and swinging with regard to vascular disease risk

This prospective 6-year follow-up study of 176 patients treated with antihypertensive drugs investigates the extent to which an excessive circadian blood pressure (BP) amplitude (above the 90th percentile of gender- and age-matched peers) contributes to the risk of adverse vascular outcomes (coronary events, ischaemic stroke, renal failure and retinal bleeding). The results are compared with those based on the standard deviation (SD) of BP and a measure of 'dipping' (night-time vs daytime BP difference). A relative risk invariably larger than unity is found for 'over-swingers', that is for patients with an excessive circadian BP amplitude, and with one exception also for patients with an SD in the upper decile of the distribution. A classification of patients as dippers vs non-dippers does not detect any statistically significant difference in the incidence of adverse vascular outcomes in the sample investigated. A combination of ambulatory or manual BP monitoring and chronobiological data analysis and interpretation facilitates the diagnosis of an excessive circadian BP amplitude and can serve to guide the timing of treatment, not only for lowering BP but also to reduce BP variability in particular, an excessive circadian amplitude. The latter condition, and an SD in the upper decile of the distribution, in this order, were associated with the largest increase in risk for ischaemic stroke and nephropathy. The excessive circadian BP amplitude constitutes an a priori no-win situation in the case of reliance upon conventional casual measurements, since in this condition, the BP is elevated only during part of the day. Thus, if casual BP measurements are taken when pressures are acceptable, the patient is likely to be left untreated, but would remain at a very high risk of developing vascular disease. Conversely, should the patient be examined when pressures are high, drugs may be prescribed that may lower the BP too much when given at the wrong time when, unknowingly, pressures are already spontaneously low and may barely suffice for perfusion. Since some antihypertensive drugs can reduce both BP and BP variability, further studies are required in order to examine whether treatment aimed at reducing an excessive circadian BP amplitude improves prognosis in subjects with high BP variability.