Lumped-parameter respiratory mechanics model, in both volume-pressure (panel A) and electrical (panel B) system analogs.

Each non-rigid compartment has a volume V (black), pressure P, (black) and associated compliance C (green, for emphasis) that is a function of the transmural pressures (purple) across the compartment boundaries. Air flows (red) across resistances R and inertance I (blue) are positive in the direction of the arrows. Circular yellow arrows indication direction of loop summations in Eq (3). Subscripts: airway opening ao, upper u, collapsible c, small peripheral s, alveolar A, viscoelastic ve, lung elastic el, transmural tm, pleural pl, chest wall cw, muscle mus.