Figure 11.

Schematic illustration of the mechanics of pulse propagation in an artery. Graphs show spatial variation of pressure and flow rate. Large arrow shows direction of propagation. Gray area represents artery, and small arrows indicate local fluid velocities. A. Short high-pressure pulse propagating in positive x-direction. At the leading edge of the pulse, fluid is accelerated by the negative pressure gradient. This produces a negative spatial gradient of flow rate. By conservation of mass, fluid accumulates in this region, and wall must move outwards. At the trailing edge of the pulse, fluid is decelerated by the positive pressure gradient, producing a positive spatial gradient of flow rate, and inward wall movement. B. Short high-pressure pulse propagating in positive x-direction. Mechanism is as in A, but with reversed velocities. Note that an arbitrary (positive or negative) x-independent velocity can be superimposed on the indicated velocities without affecting the mechanism. The x-scale is greatly compressed here for illustrative purposes. In reality, the systolic pulse wave is much longer than the diameter (and the length) of the artery.