Abstract-Ambulatory arterial stiffness index (AASI), a measure based on the relative behavior of 24-hour systolic and diastolic blood pressure (BP), has been suggested as a marker of arterial stiffness and a predictor of cardiovascular mortality. However, a narrow range of diastolic BP values over the 24 hours tends to flatten the regression slope and to artificially increase AASI. We explored the possible influence of different ranges of 24-hour diastolic BP fluctuations, such as those related to nocturnal BP fall, on AASI, and on its relationship with target organ damage. In 515 untreated hypertensive patients, AASI was directly related to age (rϭ0.30) and 24-hour systolic BP (rϭ0.20), whereas it was inversely related with nocturnal systolic and diastolic BP reduction (rϭϪ0.28 and Ϫ0.46, respectively; all PϽ0.001).A direct relationship was found between AASI and left ventricular mass index (rϭ0.17; PϽ0.001), but this relation was no longer significant after adjustment for age, sex, body mass index, daytime systolic BP, and day-night systolic BP reduction (all PϽ0.05). AASI was directly related to carotid-femoral pulse wave velocity, an intrinsic measure of aortic stiffness (rϭ0.28; PϽ0.001), but no independent relation was found in a multiple linear regression. Our conclusions are as follows: (1) AASI is strongly dependent on the degree of nocturnal BP fall in hypertensive patients; (2) there is no significant relation between AASI and left ventricular mass after proper adjustment for confounders; and (3) the relation between AASI and a widely accepted measure of aortic stiffness, such as pulse wave velocity, is weak and importantly affected by other factors. The slope was assumed as a global measure of arterial compliance, and its reciprocal (1 minus the slope), named ambulatory arterial stiffness index (AASI), was taken as a measure of arterial stiffness. The rationale underlying this assumption is that, for any given increase in distending arterial pressure, systolic and diastolic pressures tend to increase in a parallel fashion in a compliant artery, whereas in a stiff artery, the increase in systolic pressure is accompanied by a lesser increase, or even by a decrease, in diastolic pressure. In an analysis of the Dublin Outcome Study, Dolan et al 2 showed that the AASI is able to predict cardiovascular mortality in hypertensive patients. Other studies have also shown recently that this index is associated with preclinical target organ damage in hypertension. 3,4 However, several factors other than arterial stiffness may affect the regression slope of diastolic on systolic BP, and among them the range of variation in diastolic BP levels over the 24 hours may play an important role. Because of mathematical reasons, in a regression model, the range of the dependent variable (in this case, 24-hour diastolic BP) influences the regression slope. For narrow ranges of the dependent variable, B unavoidably tends to 0, thus increasing AASI. As shown by Dolan et al (see Figure 1 in their article), 2 patients with a s...
Metabolic syndrome is a powerful predictor of cardiovascular disease in hypertension, and large-artery stiffness is increasingly recognized as a cardiovascular risk factor. We hypothesized that the adverse prognostic significance of the metabolic syndrome in hypertension might be explained in part by its association with aortic stiffness. A total of 169 newly diagnosed, never treated, nondiabetic patients with essential hypertension (men 55%, 48+/-11 years) were classified by the presence (n=45) or absence (n=124) of the metabolic syndrome. All patients underwent aortic and upper limb pulse wave velocity determination by means of an applanation tonometry-based method. Aortic pulse wave velocity had a direct correlation with office and 24-hour systolic pressure (r=0.42 and 0.31, respectively), as well as with waist circumference (r=0.35, all P<0.001), but not with body mass index (r=0.10, P=not significant). Aortic pulse wave velocity was higher in the subgroup with the metabolic syndrome (10.0+/-2.7 versus 8.8+/-2.1 m/s; P=0.003), whereas upper limb velocity did not differ in the 2 groups (8.6+/-1.4 versus 8.7+/-1.5 m/s; P=not significant). In a multiple regression, aortic pulse wave velocity was independently associated with age, systolic blood pressure, and the metabolic syndrome. Only diastolic BP independently predicted upper limb pulse wave velocity. We conclude that in untreated hypertension, the metabolic syndrome is independently associated with a higher aortic, but not upper limb, pulse wave velocity. Central, but not general, adiposity is an important determinant of aortic stiffness in hypertension.
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