Transformation of an arterial system into a Windkessel results in isolated systolic hypertension

Abstract

The incidence of isolated systolic hypertension (i.e., increased arterial pulse pressure) is associated with changes in arterial properties accompanying advanced age, including increased diameter and stiffness of the large conductance arteries. Two competing schools of thought ascribe ISH to fundamentally different arterial system properties. The Windkessel School describes the arterial system as a compliant chamber that distends and stores blood, and relates pulse pressure to peripheral resistance and total arterial compliance (Ctot). The Transmission School describes the arterial system as a network of vessels that transmit pulses, and relates pulse pressure to the magnitude, timing and sites of pulse wave reflection. We hypothesized that the transmission description degenerates into a Windkessel when pulse wavelengths increase. Parameters effecting pulse wavelength (i.e., arterial compliances and radii) were altered in a realistic, large-scale distributed arterial system model. Model results were validated with analysis of measured human aortic pressure and flow waveforms. Results suggest that ISH occurs when compliances decrease and radii increase enough for an arterial system to degenerate into a classical (2-element) Windkessel. Pulse wave reflection thus becomes irrelevant, and decreases in Ctot are solely responsible for increased pulse pressure.