Question

Why is the presence of arteriosclerosis in the older person result in increase of systolic pressure and decrease in diastolic pressure?

Answer 1

The stiffness and narrowing of the arteries with age ( which causes increase in pressure) is called arteriosclerosis. It leads to hardening of arteries and arterioles. It is also an indication of vascular ageing and it reduces the capacitance ( ability of blood vessels to increase volume of blood it holds with out large increase in blood pressure) of large arteries and increases pulse wave velocity which leads to increased systolic blood pressure.  

Stiff arteries are less flexible and elastic due to which blood does not flow through them easily leading to low diastolic blood pressure. Also less elastic recoil ( inherent resistance of blood vessel tissue to change in shape and tendency to return to its original shape after deformation) doesn't support high diastolic blood pressure.

Thus large artery stiffness and peripheral vascular resistance (resistance of circulatory system to flow of blood) together leads to increased systolic blood pressure and decreased diastolic blood pressure.