FIGURE 2.

Schematic of the in silico simulator. Left and right atria (LA, RA) and ventricles (LV, RV) contraction is regulated by activation functions (ac, vc). Valves are represented by a diode and a resistance (Rmv, Rav, Rtv, Rpv). The i_th vascular compartment is represented by resistance (Ri), inertance (Li), and compliance (Ci). Suffix refer to: ascending and descending aorta (aa, da), upper body (ub), kidneys (kid), splanchnic circulation (sp), left and right legs (ll, rl), inferior and superior vena cava (ivc, svc), arterial, and pulmonary circulation (pa, pv). The baroreflex control uses the difference ascending aortic pressure (Paa)—reference pressure (Paa _Ref ) as input, and controls heart rate, heart contractility, arterial resistances and venous tone. The metabolic control acts locally in the upper body, kidneys, splanchnic circulation and legs. In the figure it is represented only for the left leg for brevity. It takes the difference O₂ concentration (C _O2llv )—reference concentration (C _O2llvRef ) as input, and controls R _lla and R _llv as output. The ventilation control takes the arterial O₂ and CO₂ partial pressure in the upper body as input and controls the tidal volume and ventilation frequency as output. The ventilation model includes a resistance (Raw) and a compliance (Elungs) and provides the intrathoracic pressure (Pt) as output, sent to the vessels of the circulation model within the thorax. The model of gas exchange in the lungs takes into account the amount of ventilated air and the difference in O₂ and CO₂ partial pressure between the air and the blood side in the alveoli. Gas transport in the peripheral tissues is illustrated only for the left leg for brevity. It takes into account the O₂ consumption (V _O2ll ), the respiratory quotient (RQ), and the arterial and venous blood flow.