The importance of large artery pressure-volume curve changes in hypertension studied with a closed-loop circulatory model

A closed-loop model of the cardiovascular system was used to study the effect of the pressure-volume (P-V) curve of the large arteries on systemic blood pressure. Three types of P-V alterations were considered : constant compliance with altered unstressed volume, compliance change, and nonlinear P-V with altered unstressed volume. It was hypothesized that the P-V relation of large arteries can alter blood pressure equally as well as the pressure-flow relation of the small resistance vessels. Results showed that a compliance change or P-V curve shift were equally capable of affecting average blood pressure, with the compliance, in addition, able to affect pulse pressure. The nonlinear P-V relationship with P-V shift most resembled hypertension and was highly effective in achieving elevated pressures and pulse pressure. The authors found that changes in peripheral resistance were not necessary to alter blood pressure. If resistance was allowed to vary such that cardiac output is held constant, that is, whole body autoregulation, the effects of large artery P-V alterations were augmented. Hence, peripheral resistance was only required to change when cardiac output was restored to pre-altered pressure levels. The authors conclude that a change in the pressure-volume curve of large arteries is a necessary condition of chronic elevation in blood pressure and is observable from the systemic arterial pressure-volume plane. Detailed knowledge of the P-V curve permits identification of the possible sources of hypertension relative to the large arteries.