Design of a new variable-ventilation method optimized for lung recruitment in mice.

Variable ventilation (VV), characterized by breath-to-breath variation of tidal volume (Vt) and breathing rate (f), has been shown to improve lung mechanics and blood oxygenation during acute lung injury in many species compared with conventional ventilation (CV), characterized by constant Vt and f. During CV as well as VV, the lungs of mice tend to collapse over time; therefore, the goal of this study was to develop a new VV mode (VV(N)) with an optimized distribution of Vt to maximize recruitment. Groups of normal and HCl-injured mice were subjected to 1 h of CV, original VV (VV(O)), CV with periodic large breaths (CV(LB)), and VV(N), and the effects of ventilation modes on respiratory mechanics, airway pressure, blood oxygenation, and IL-1beta were assessed. During CV and VV(O), normal and injured mice showed regional lung collapse with increased airway pressures and poor oxygenation. CV(LB) and VV(N) resulted in a stable dynamic equilibrium with significantly improved respiratory mechanics and oxygenation. Nevertheless, VV(N) provided a consistently better physiological response. In injured mice, VV(O) and VV(N), but not CV(LB), were able to reduce the IL-1beta-related inflammatory response compared with CV. In conclusion, our results suggest that application of higher Vt values than the single Vt currently used in clinical situations helps stabilize lung function. In addition, variable stretch patterns delivered to the lung by VV can reduce the progression of lung injury due to ventilation in injured mice.