Background: Vascular aging is characterised by structural changes: wall thickening and an increase in lumen diameter, together with a functional increase in arterial stiffness. We investigated the longitudinal structural and functional changes that occur in the aortic wall over a 5 year follow-up period.

Methods: Subjects were 472 female twins (mean ageSD, 57.9±8.6 years at baseline). Measures of diameter and intima-media thickness (IMT), averaged from the carotid and femoral artery, and carotid-to-femoral pulse wave velocity (PWV) were made at two time-points, first between 2008–2014 and then on a second occasion an average of 4.7±3.0 years later. Young’s incremental elastic modulus was estimated from the simplified Moens-Korteweg equation: PWV=√Eh/D, where h is the wall thickness and D is diameter.

Results: There was a significant increase in intima-media thickness (0.064±0.01 cm at baseline and 0.070±0.01 cm at follow-up, P<0.0001), diameter (0.75±0.06 cm at baseline and 0.76±0.07 cm at follow-up, P<0.0001) and PWV (9.15±1.8 at baseline and 9.75±1.8 m/sec at follow-up, P<0.0001), over the five-year follow-up period. The influence of the estimated increase in elastic modulus (10.2±4.0 and 10.7±4.1 10⁶dynes/cm², at visit one and two respectively, P=0.001) on PWV was amplified by intima-media thickness increasing more than arterial diameter (10.5% versus 2.2%).

Conclusion: In our cohort of middle age to older women, increase in aortic wall thickness to lumen diameter was the most marked structural change and could potentially amplify the increase in PWV produced by intrinsic stiffening of the aortic wall.