3 years ago

The circadian blood pressure variability: There is a signal in the noise

Arthur Sá Ferreira, Felipe Amorim Cunha

For centuries, we acknowledge the existence of physiologic rhythms and their close relationship with health and life.1, 2 In particular, the circulatory system shows a complex and mutable rhythmic pattern that ultimately continuously perfuse all body tissues.1, 3 Systolic and diastolic blood pressures oscillates over short‐ (eg beat‐to‐beat, day‐to‐night) to long‐term (eg visit‐to‐visit, seasonal) periods due to mechanical (eg abdominal and thoracic pressures during ventilation), neural central or peripheral (eg sympathetic and parasympathetic activity), and humoral (eg renin‐angiotensin, insulin‐glucagon, melatonin secretion) quasi‐periodic physiologic events, among others.1-5 Those oscillations are superimposed to non‐periodic events that have effects on the blood pressure (eg behavioral, environmental) or are even unrelated to the circulatory function itself (eg measurement artifact, device precision).2 Collectively, the blood pressure variability (BPV) has both deterministic and indeterministic information6 about the functioning of the circulatory system and its interaction with other systems and the environment, as well as unwanted information—the challenge remains distinguishing them. Clinically, BPV shows the extent to which the body adapts to stressful conditions such that those rhythmic patterns are linked to the pathophysiology of cardiovascular diseases (CVD).1-5

Ambulatory blood pressure monitoring (ABPM) has been used since the late 60s7 for estimating BPV and advances in biomedical instrumentation and digital signal processing allied to the continued clinical interest in this subject helped increasing its use.8 The recent study by Tadic et al9 highlights this by analyzing ABPM data of the Pressioni Arteriose Monitorate E Loro Associazioni (PAMELA) study10 to investigate the relationship of cognitive function with blood pressure and BPV in the general population. The cognitive function was assessed using the Mini‐Mental State Examination,11 with a cut‐off value of <24 points to classify the population as showing worse cognitive function. ABPM collected each 20 minutes over 24 hours was used to estimate traditional parameters of BPV, namely the standard deviation (SD) and the coefficient of variation of systolic and diastolic blood pressures. They also estimated the individual residual variability12, 13 as the sum of the squared differences between the individual ABPM recording and the sum of frequency components that accounts for ≥95% of the systolic and diastolic pressures SD obtained from the population‐averaged ABPM recordings. Their analyses revealed, among other results, that patients with worse cognitive function have higher individual residual variability that cannot be explained by those cyclic patterns, except for subjects aged >75 years. Their findings support an inverse relationship between blood pressure and cognitive function in the general population and that the individual residual variability w

-Abstract Truncated-

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