The gas exchange simulator is described as a steady state solution of a 50 compartment ventilation-perfusion model. Several built-in processes are taken to alter gas exchange parameters. Alveolar shunt arises in a fashion that depends directly on accumulated lung edema. Hyperinflation is directly linked to dead space and is inversely related to the shunt fraction associated with lung edema. Peripheral Gas Exchange Peripheral gas exchange is handled by assuming delivery independent consumption above a critical point, and delivery dependent consumption below it.
Demand varies with suppressible muscle activity.
Lactate production occurs whenever oxygen delivery is too low to support full oxidative metabolism, and lactate absorption occurs when oxygen is in good supply. The former describes the passive mechanics of the chest wall and lung. The topology of the respiratory mechanics simulation is shown at the right, and the static pressure volume curve for the lung is calculated by simultaneous solution of the same pressure in the individual lobes, subject to the applied external pressures. The dynamics simulation is a continuous solution of the equations for fluid flow between the lobes. Sim Bio Sys does treat the fluid as incompressible, but this introduces only a small error.