Abstract
In recent years, there has been interest in evaluating the morbidity and mortality risk of circadian, diurnal, or noctur-nal blood pressure variation. Variation is a normative property of blood pressure, necessary for survival. Like many physio-logical functions, blood pressure undergoes allostasis, meaning that the body does not defend a particular blood pressure value, but rather blood pressure maintains bodi-ly stability through continual change that is initiated by constantly fluctuating internal and external environmental stimuli. Be-cause 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 appro-priateness for the circumstance, which requires quantification of the sources and extent of normative blood pressure respons-es to everyday living. These responses will vary among populations due to evolutionary genetic differences. The incon-sistency 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.
Highlights
Since the report of the first measurement of blood pressure by Stephen Hales in 1733, its inherent variability has been well known [1, 2] but largely ignored [1, 3]
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
Practitioners of cardiovascular medicine even today are largely at a loss regarding how to deal with the continuous variation of blood pressure clinically, primarily because, as George Pickering noted early on, the entire medical focus on blood pressure is differentiating a dichotomy of normalcy and pathology [4]
Summary
Since the report of the first measurement of blood pressure by Stephen Hales in 1733, its inherent variability has been well known [1, 2] but largely ignored [1, 3]. As automatic ambulatory blood pressure monitoring technology emerged in the late 1970’s and improved through the 2000’s, the effects of various typical behaviors on blood pressures were evaluated, first using intra-arterial devices and later using monitors that employed either auscultatory or oscillometric technology [1, 22] These studies, mostly undertaken by biobehavioral researchers, were designed to quantify the intraindividual variation in pressure associated with psychological, sociological, and environmental sources [3, 23]. The idea is that levels in these parameters fluctuate to adapt the individual to ever changing circumstances, so that there is a connection between external conditions and the body’s ability to meet the demands imposed by them, which is all regulated by the brain [3] These measurable physiological systems anticipate demand and have a multitude of stable states that occur as responses to continuously changing environmental strains, either real or perceived. Variation is what gives blood pressure its adaptive value, and is perhaps the single most important normative property of blood pressure, for without it humans could not survive [22]
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