Pulsatile Pressure and Flow through Distensible Vessels.

• The problems of characterizing pulsatile patterns of pressure and flow in the arterial system are intriguing and complex. Ejection of blood from the left ventricle initiates nonlinear transients in pressure and flow at the root of the aorta. These transients initiate complex pulse patterns that are propagated throughout the arterial tree. Some of the factors that must be reckoned with in an analysis of these patterns are itemized in the list that follows: 1) The force initiating the transients is itself complex; the velocity of ventricular ejection increases rapidly with the opening of the aortic valve, then declines slowly to reach a negative nadir with the closure of the aortic valve. 2) The distensibility of the walls of the arteries receiving this positive increment of pressure and flow has an important influence on pulse patterns. This physical property of the arterial wall is also responsible for changes in configuration and velocity of the transients as they pass over the arterial tree. The pulsatile patterns are further distorted by 3) frictional losses of energy with both positive and negative flow of the blood, and by the 4) branching and tapering architecture of the arterial tree. 5) The resistances to forward motion of blood through the distal arteriolar beds also have their effects on the contours of the arterial pulses observed upstream.