We investigated individual and combined effects of increased aortic stiffness and resistance on (pulse, PP) pressure with aging. Wave travel and reflection determine the contribution of the arterial system to pressure wave shape and magnitude. Reflections occur at all branch points, and these local reflections cause amplification (distal pressure equal forward plus backward pressure). We used an anatomically accurate model of the human systemic arterial tree in this analysis. We found that ascending aorta pressure wave shape and Reflection Magnitude (PP_forw/(PP_backw+PP_forw)) are not changed with changes in peripheral resistance. This suggests that pressure wave shape depends on multiple local reflections, i.e., large artery (aortic) geometry and stiffness. Mean pressure depends on resistance only. Over the physiologic range changes in geometry have little effect, but stiffness does. Using aortic PWV and area as function of age (20–80 years, PWV 4–10m/s) we calculated aortic stiffness. For constant resistance systolic pressure increased and diastolic pressure decreased with age (stiffness). An increase in peripheral resistance of 20% and decrease in CO of 5% between 20 and 80 yrs, increased both systolic and diastolic pressures but left PP unaltered. Both effects together let systolic and mean pressure increase (106–161 and 93–108mmHg, resp.) and diastolic pressure decrease (81–71mmHg).

We conclude that increased pulse pressure results from increased aortic stiffening not from increased vascular resistance. Increased mean pressure results from increased resistance. Both effects together causes increased systolic pressure and may cause a decrease in diastolic pressure, depending on the resistance change.