The Adaptive Value and Clinical Significance of Allostatic Blood Pressure Variation.

In recent years, there has been interest in evaluating the morbidity and mortality risk of circadian, diurnal, or nocturnal blood pressure variation. Variation is a normative property of blood pressure, necessary for survival. Like many physiological functions, blood pressure undergoes allostasis, meaning that the body does not defend a particular blood pressure value, but rather blood pressure maintains bodily stability through continual change that is initiated by constantly fluctuating internal and external environmental stimuli. Because of its allostatic and adaptive properties, the blood pressure response to unusual situations like a visit to the clinic can lead to misdiagnosis of hypertension. However, blood pressure variation is mostly ignored when evaluating hypertension, which is an arbitrary dichotomy. Whether variation is indicative of pathology should be determined by assessing its appropriateness for the circumstance, which requires quantification of the sources and extent of normative blood pressure responses to everyday living. These responses will vary among populations due to evolutionary genetic differences. The inconsistency of reports regarding aspects of ambulatory blood pressure variation as cardiovascular risk factors likely results from the fact that the measures used do not reflect the actual nature of blood pressure allostasis.