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

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 ≤60 and >60 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 (P<0.05) 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 (P<0.05) and comparable contributors (P difference >0.05) 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.