Mathematical models of passive, pressure-controlled ventilation with different resistance assumptions

A class of one-compartment models for pressure controlled mechanical ventilation is studied. The resistive pressure term in the general model is of the form: R"1Q + R"2Q|Q| where Q denotes the flow in and out of the compartment. This Rohrer-type model (R"1 0 and R2 0) is compared against the special cases: 1.(i) R"1 = R"L and R"2 = 0 (linear model); 2.(ii) R"1 = 0 and R"2 = R"N (nonlinear model). For clinical ranges of resistances (R"2 and R"2), compliance (C), applied pressure (P"s"e"t), frequency (f), and inspiratory time-fraction (D), the Rohrer model is used to compute the key outcome variables: tidal volume, average volume, end-expiratory pressure, and mean alveolar pressure. These values are compared against those obtained using equivalent RL and RN values. It is demonstrated that for clinically relevant ranges of the physiologic and ventilator parameters, little difference is observed between the Rohrer and nonlinear model.