Arterial Blood Pressure
When arterial pressure is measured using a sphygmomanometer (i.e., blood pressure cuff) on the upper arm, the systolic and diastolic pressures that are measured represent the pressure within the brachial artery, which is slightly different than the pressure found in the aorta or the pressure found in other distributing arteries. As the aortic pressure pulse travels down the aorta and into distributing arteries, there are characteristic changes in the systolic and diastolic pressures, as well as in the mean pressure. The systolic pressure rises and the diastolic pressure falls, therefore the pulse pressure increases, as the pressure pulse travels away from the aorta. This occurs because of reflective waves from vessel branching, and from decreased arterial compliance (increased vessel stiffness) as the pressure pulse travels from the aorta into systemic arteries. There is only a small decline in mean arterial pressure as the pressure pulse travels down distributing arteries due to the relatively low resistance of large distributing arteries.