Introduction: The return time of the reflected wave as a function of age has been reported to decrease by some but unaltered by others (1). The increased pulse wave velocity (c) suggests earlier return with age, but the effect of reflection (2) and foot-foot velocity (c_f-f) of the backward wave are not accounted for.

Method: We consider the aorta to be a uniform tube (phase velocity, c), with at its distal end the impedance of lower body and legs. With age the aortic wall stiffens and c increases. We assume, for simplicity, the distal bed not to change.

Results: With stiffer aorta, c_f-f of the forward wave (∼c) is increased. However, the phase angle of the reflection coefficient becomes more negative, i.e., the apparent aortic length increases. The reflected wave contains few high harmonics, and its foot pertains to low frequencies traveling with a high c_f-f=c_app (we found c_app≈2.5c), this high speed contributes little to the return time. Thus, the stiffer aorta increases forward wave speed which shortens the return time, while the phase angle of reflection lengthens the return time (2). The two opposite effects are comparable in magnitude, and therefore the return time is quite independent of age.

Conclusion: With age, the forward wave travels faster (increased c_f-f), but the increased phase of the reflection coefficient counteracts this and therefore the return time changes little with age.