The pressure wave originated by the systolic discharge of blood into the aorta. It is not due to the passage of the ejected blood but is the result of the impact being transmitted through the arterial walls. The velocity in the aorta may be as high as 500 cm/sec and as low as 0.07 cm/sec in capillaries. The speed of transmission varies with the nature of the arterial wall, increasing with age as the arteries become less resilient. Thus in arteriosclerosis, the velocity is increased over normal.