Figure 7-10 Schematic diagram depicting the three-element Windkessel model of the arterial circulation. Diode A represents the aortic valve. Time-dependent blood flow [F(t)] and blood pressure [P(t)] entering the arterial system first encounters the resistance of the ascending aorta (characteristic aortic impedance [Zc]). Further flow is dictated by total arterial resistance (R) and total arterial compliance (C), the energy storage component of the arterial vasculature. (Adapted from Hettrick DA, Pagel PS, Warltier DC: Differential effects of isoflurane and halothane on aortic input impedance quantified using a three-element Windkessel model. Anesthesiology 83:361–373, 1995.)