Flow-controlled expiration (FLEX) homogenizes pressure distribution in a four compartment physical model of the respiratory system with chest wall compliance.

Flow-controlled expiration (FLEX) has been shown to attenuate ventilator-induced lung injury in animal models. It has also shown to homogenize compartmental pressure distribution in a physical model of the inhomogeneous respiratory system having independent compartments. We hypothesized that the homogenizing effects of FLEX are also effective in this regard when the independence of compartments is suspended by simulated chest wall compliance.A four compartment physical model of the respiratory system having chest wall compliance (137 ml/cmHO) was developed. Two of the four compartments had high compliance (18 ml/cmHO) and two had low compliance (10 ml/cmHO). These compartments were each combined with either high (6.8 cmHO·s/l) or low resistance (3.5 cmHO·s/l). The model was ventilated in the volume-controlled ventilation mode with either passive expiration or with FLEX. The maximal pressure differences (Δ) and the maximal differences of mean pressure (Δ) between the compartments during expiration were determined.With passive expiration Δreached up to 3.4 ± 0.03 cmHO but only 0.9 ± 0.01 cmHO with FLEX ( < 0.001). Maximal differences of Δwere significantly lower with FLEX as compared to passive expiration (extending up to 0.4 ± 0.04 cmHO versus 2.0 ± 0.15 cmHO, < 0.001).The homogenizing effects of FLEX on compartmental pressure distribution could be reproduced in a more complex physical model of the inhomogeneous respiratory system having chest wall compliance and might be a mechanism underlying the lung protective effects of ventilation with FLEX.