Short- and long-term blood pressure variability: present and future.

It has long been known that blood pressure (BP) is characterized by an array of spontaneous variations. That is, BP values vary markedly within the 24 hours because of day-night changes but also because of differences among hours, minutes, and even adjacent beats. They also show variations over more prolonged periods because of differences among days, months, and seasons, also with a trend for systolic BP to increase over the years and for diastolic BP to display an age-related biphasic change. This article summarizes current knowledge on short-term (within the 24 hours) and long-term BP variability. Mention will be made of the following: (1) factors responsible for BP variations and mechanisms through which they occur; (2) the relationship of BP variability with BP mean values in absence and during antihypertensive treatment; and (3) the prognostic significance of BP variability. Current limitations of the studies on BP variability will be also discussed to emphasize what future studies should address.