Dynamic alveolar mechanics and ventilator-induced lung injury

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Abstract
To review the mechanism of dynamic alveolar mechanics (i.e., the dynamic change in alveolar size and shape during ventilation) in both the normal and acutely injured lung; to investigate the alteration in alveolar mechanics secondary to acute lung injury as a mechanism of ventilator-induced lung injury (VILI); and to examine the hypothesis that the reduced morbidity and mortality associated with protective strategies of mechanical ventilation is related to the normalization of alveolar mechanics. This review is based on original published articles and review papers dealing with the mechanism of lung volume change at the alveolar level and the role of altered alveolar mechanics as a mechanism of VILI. In addition, data from our laboratory directly visualizing dynamic alveolar mechanics is reviewed and related to the literature. The mechanism of alveolar inflation in normal lungs is unclear. Nonetheless, normal alveoli are very stable and change size very little with ventilation. Acute lung injury causes marked destabilization of individual alveoli. Alveolar instability causes pulmonary damage and is believed to be a major component in the mechanism of VILI. Ventilator strategies that reduce alveolar instability may potentially reduce the morbidity and mortality associated with VILI.