The flexible (compliant) aorta and large muscle arteries
The flexibility or compliance of arterial walls determine the flowspeed of the pulse waves. When blood is ejected into the aorta, the pressure wave is caused by the distension of the elastic aortic walls during systole. The ejected blood has kinetic energy and the stretched aortic wall stores this kinetic energy as potential energy.
During diastole, the aortic wall recoils and the stored energy is converted back to kinetic energy. This energy maintains onward flow of blood during diastole (Diastolic BP). This effect converts pressure waves generated at the heart into a positive and constant pressure at the tissues and end-organs, which is important for micro circulation. The kinetic energy, importantly, supports blood perfusion through the myocardic muscle, therefore aortic compliance is vital to support and energise the heart muscle.
This process is best demonstrated by the Windkessel model.
The Inflexible (non-compliant) aorta and large muscle arteries
As the aortic wall loses elasticity (age, hypertension, atherosclerosis, diabetes, obesity, smoking, inactivity), the accommodation of the systolic volume reduces with increasing pressure. The pulsatile pressure increases and the speed of the pulse waves increases.
The increased pulsatile action is detrimental to the microcirculation in the kidneys and brain leading to kidney damage and cognitive decline. The microcirculation in the brain is also susceptible to damage resulting in a stroke. Increased arterial stiffness with increased CVD risk happens before BP increases, therefore not detected by regular BP measurement.