Altered circadian rhythm of blood pressure and cerebrovascular damage.

An abnormal circadian rhythm of blood pressure [i.e. a lesser or 'reverse' nocturnal fall of blood pressure (nondippers)] is associated with cerebrovascular damage including intracranial hemorrhaging, thrombosis, and vascular dementia. Silent cerebrovascular damage such as lacunae and periventricular hyperintensity lesions is not infrequently detected in apparently healthy hypertensive elderly subjects by brain magnetic resonance imaging and also is more common among nondippers than it is among dippers. Although no exact cause-effect relationship is known, a decrease in nocturnal fall of blood pressure might be secondary to a site-specific injury to the brain resulting in an impairment of central autonomic nervous system functioning. Besides nondipping, evidence suggests that the extreme dipping (a marked nocturnal fall of blood pressure) should be considered a type of abnormal diurnal blood pressure variation in elderly patients with hypertension who are likely to have advanced silent cerebrovascular damage. The pathogenic significance of 'extreme dipping' might be an 'artificial' excess reduction in blood pressure at night beyond the lower limit of blood pressure in the autoregulation of cerebral blood flow that is probably induced by antihypertensive agents. It is also possible that a greater blood pressure variability in extreme dippers itself accelerates the hypertensive target-organ damage. Prospective follow-up of subjects with these distinct subtypes of abnormal circadian blood pressure variation as well as trials comparing a group of treated patients with various degrees of dipping with a group of untreated counterparts may establish the validity of assessing these distinct circadian rhythms of blood pressure as a useful clinical parameter in the management of hypertension.