The clinical relevance of extreme dipping

Hypertensive patients who demonstrate an exaggerated circadian blood pressure rhythm are known as 'extreme dippers'. 'Non-dippers' are those patients whose blood pressure remains elevated throughout the night. There are many cross-sectional studies in which greater hypertensive target organ damage has been seen in non-dippers. However, almost as many studies have demonstrated a positive association between organ damage and the magnitude of the circadian change in blood pressure. This apparent paradox may be explained by both nighttime pressure and the daytime rise in blood pressure being independently and positively associated with severity of hypertensive target organ damage. More recently, a number of prospective cohort studies have suggested that 'extreme dippers' are at a greater risk of cardiovascular events than those with more moderate circadian rhythms. These small studies have been criticised as being likely to include significant random and systematic errors. Large prospective studies will need to address issues such as optimal quantification of circadian rhythms, poor reproducibility and the likely confounding of results due to diverse antihypertensive therapies, if the association between dipping and adverse cardiovascular outcome is to be further clarified.