Does Wave Reflection Dominate Age-Related Change in Aortic Blood Pressure Across the Human Life Span?

Abstract

Abstract-Aortic systolic and pulse pressure rise with age because of aortic stiffening. Two factors are responsible: a larger incident wave because of increased aortic characteristic impedance and premature return of wave reflection from peripheral sites. This study aimed to determine the relative contribution of each factor before and after age 60 years. Aortic pressure waveforms were generated for 3682 healthy subjects using a generalized transfer function applied to radial pressure waveforms recorded by applanation tonometry. Linear regression and product of coefficient mediation analysis were performed in the cross-sectional cohort to determine the yearly contribution of the incident and reflected waves (waves measured as first systolic peak and augmented pressure, respectively) to aortic systolic and pulse pressure elevation with age. This was done separately for subjects Յ60 and Ͼ60 years of age, with both sexes initially pooled and subsequently separated. Analyses were repeated with correction for height, weight, heart rate, and mean arterial pressure. Before age 60 years, the reflected wave was a greater (PϽ0.05) contributor to age-related aortic systolic and pulse pressure elevations, with no significant contribution of the incident wave in this age group in sex-pooled analysis. After age 60 years, both incident and reflected waves were significant (PϽ0.05) and comparable contributors (P difference Ͼ0.05) to age-related aortic systolic and pulse pressure elevations. This general pattern was observed in both sexes and persisted after correction for confounders. Wave reflection is important across the life span, whereas aortic characteristic impedance contributes significantly only beyond age 60 years. Key Words: aging Ⅲ blood pressure Ⅲ arterial stiffening Ⅲ hypertension Ⅲ aorta A ge-related increases in systolic and pulse pressures 1,2 contribute to progressively rising cardiovascular risk and cardiovascular morbidity and mortality. 3,4 As part of the normal aging process, the aorta undergoes structural changes, progressively stiffening because of cyclic strain, causing fracture of elastin lamellae in the tunica media and fibrous remodeling of the aortic wall. 5 Aortic stiffening is deemed responsible for age-related increases in systolic and pulse pressures 5,6 and exerts direct and indirect effects. 7 Directly, aortic stiffness increases aortic characteristic impedance and, therefore, increases the magnitude of the peripherally traveling (incident) pressure wave generated by ventricular ejection. Indirectly, increased aortic stiffness alters the timing and magnitude of wave reflection from the periphery, such that the aorta is subjected to progressively early return of a larger reflected pressure wave with advancing age. The phenomenon of wave reflection forms the traditional view regarding age-related blood pressure elevation. 8,9 Mitchell et al, 10,11 however, have suggested that wave reflection is irrelevant in women over age 60 years and minor in men over age 60 years and propose that the incident...

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