Simulation of Exercise-Induced Syncope in a Heart Model with Severe Aortic Valve Stenosis

Figure 2

Top records. The time course of AoP, MAoP, CO, CVV, Sy, and LAtP in initial conditions (50 s–70.5 s), after LV contractility is decreased (70.5 s–110.5 s), after aortic stenosis (110.5 s–150.5 s), after exercise (150.5 s–240.5 s), and after failure of homeostasis (240.5 s onwards). If a parameter is changed, due to the homeostatic negative feedback, a transient phenomenon shows up, but very soon a new steady state is established. As expected, exercise (decreased peripheral resistance and MAoP reset) results in an increased Sy, and consequently, increased heart rate, CO, MAoP, and systolic AoP. Steady state levels of variables, depending on the type of homeostasis failure, are shown in the bottom records in columns (a–d) (530 s–550 s of simulation time). Failure of homeostasis results in a dramatic change of almost all variables. Steady state levels of variables (interval 530 s–550 s of simulation time) depend on the type of homeostasis failure. At heart rate 120/min and Sy equal to 1 FGU, AoP is decreased and pulse pressure lowered (a). A decrease in Sy results in a further decrease of AoP and MAoP (b). At a heart rate of 45/min and a Sy equal to 0.5 FGU, the AoP and MAoP are extremely low (c). If the Sy is increased to 1.5 FGU, the MAoP is low and the pulse pressure very large (d).