Pulse Wave Analysis and Velocity
A Sphygmocor device measures arterial stiffness and central blood pressure using Pulse Wave Analysis (PWA) and Pulse Wave Velocity (PWV). Arterial stiffness is an important pathogenic factor for hypertension and cardiovascular risk.
Pulse wave analysis (PWA) is a technique that records high-fidelity peripheral pressure waveforms and corresponding central pressure waveforms, which then generates the augmentation index. The augmentation index (AI) is an indirect measure of arterial stiffness. It is calculated as augmentation pressure divided by (pulse pressure ×100) to give a percentage. With an increase in stiffness there is a faster propagation of the forward pulse wave as well as a more rapid reflected wave. PWA is easily obtained by placing a brachial cuff on the arm, and inflating it to measure peripheral blood pressure, until multiple waveforms are captured. Central (ascending aortic) blood pressure is simultaneously derived from the peripheral waveforms using a validated transfer function.
Pulse Wave Velocity (PWV) is the gold standard non-invasive technique for measuring arterial stiffness, or the rate at which pressure waves move down the blood vessel. It is obtained by placing a femoral cuff on the leg, and obtaining carotid artery pulse waves by using a micro manometer-tipped tonometer as shown in Figure 1. The time taken for the arterial pulse to propagate from the aorta to the femoral artery gives a measure of central arterial stiffness.