The stiffness of the aorta will be determined by calculating the pressure-strain elastic modulus (Ep) and the stiffness index beta (β). They are calculated from the formula Ep=[Ps-Pd]/[Ds-Dd/Dd] and β = [ln Ps/Pd[Ds-Dd]. Pressure-strain elastic modulus measurements have been utilized to measure the stiffness of the aorta and carotid arteries in both adults and children with a high reproducibility and low interobserver variability. The stiffness index beta has been proposed as a better measure of aortic stiffness because of its independence from measured blood pressure. The ability of a vessel to distend to store extra volume due to pressure effects is known as its compliance. A vessel with a higher compliance will be more "stretchy" and will therefore be more favorable to holding a greater volume of blood rather than storing a lot of pressure energy. Conversely, a vessel with a lower compliance will be less "stretchy" and therefore be more favorable to storing a lot of pressure energy rather than holding a greater volume of blood. Essentially, if two vessels are of equal size (cross-sectional flow area and volume), but one vessel has a lower compliance, then a 1 milliliter change in volume of the lower compliance (less stretchy) vessel will result in a greater pressure increase than a 1 milliliter change in volume of the higher compliance (more stretchy) vessel. Compliance will be assessed by the use of automatic border detection. This provides a continuous measure of the vessel cross-sectional area over time. Compliance is calculated by (Areamax-Areamean/mean blood pressure).