321435_Print.indd

(やまだぃちぅ) #1

systolic/diastolic blood pressure that persistently exceeds 140/90 mmHg in the


clinical setting, although the most recent guidelines for hypertension management


suggest that for individuals over 60, this cut point should be 150/90 (James et al.


2013 ). An estimated 78 million adults in the USA (33% of the population) are


reported to have hypertension (Go et al. 2013 ). Over the past five decades,


numerous clinical trials and epidemiological studies that have longitudinally eval-


uated the risks associated with varying levels of blood pressure show that hyper-


tension is a significant risk factor for cardiovascular disease and stroke (e.g., James


1991 ; Wong et al. 2012 ; James et al. 2013 ). Because of this association, the


pharmaceutical industry has produced a cornucopia of drugs designed to either


lower circulatingfluid volume, lessen arterial vasoconstriction, or promote arterial


vasodilation as a means of lowering blood pressure, so that people with hyper-


tension can presumptively decrease their risk of cardiovascular morbidity and


mortality to that of people with“normal”blood pressure levels (Wong et al. 2012 ;


James et al. 2013 ).


While the level of ausculted blood pressure measured in the physician’soffice


has been a standard of cardiovascular health determination, the circadian variation


of blood pressure, until relatively recently, has been of minimal interest. The


increasing use of automated ambulatory blood pressure monitors in cardiovascular


medicine over the past three decades has confirmed that there is enormous intraday
variability in blood pressure (James2007a; Flores 2013 ). Health conditions such as


white coat hypertension (Pickering et al. 1988 ; Ohkubo et al. 2005 ) and masked


hypertension (Ohkubo et al. 2005 ; Pickering et al. 2007 ; Angeli et al. 2010 ) have


been defined from the difference in blood pressures measured in the clinic and over


24h during daily life, and recent studies suggest that there is a significant difference


in cardiovascular morbidity risk associated with these designations (e.g.,


Konstantopoulou et al. 2010 ; Pierdomenico and Cuccurullo 2011 ; Hermida et al.


2012 ). Other aspects of the circadian variation in blood pressure, such as the


waking–sleep difference in blood pressure (dipping) (Fagard et al. 2009 ; Cuspidi


et al. 2010 ; Hansen et al. 2011 ) and the surge in pressure upon awakening (Kario


2010 ; Yano and Kario 2012 ) have also been shown to predict cardiovascular


morbidity and mortality (James 2013 ). In a recent study that pooled data from 11


international databases, the prognostic value of 24-h blood pressure variability was


evaluated in 8938 patients (Hansen et al. 2010 ). There was a median of 11.3 years


follow-up, with 1242 deaths and 1049 fatal or non-fatal cardiovascular events


across the databases (Hansen et al. 2010 ). The study evaluated the following: (1) the


standard deviation of the 24-h mean pressure weighted for the interval between


consecutive readings; (2) the average of the daytime and nighttime standard devi-


ations, weighted for the duration of the daytime and nighttime interval; and (3) the


“average real variability”(ARV24) which has been defined as the mean of the


absolute differences of consecutive measurements as risk factors for all cause and


cardiovascular morbidity and mortality (Flores 2013 ). The analysis found modest


independent relationships between diastolic ARV24 and cardiovascular mortality,


and systolic ARV24 and cardiovascular mortality. In models excluding the average
24-h blood pressure, the 24-h systolic and diastolic standard deviation predicted


148 G.D. James

Free download pdf