Alveolar Mechanics in the Acutely Injured Lung: Role of Alveolar Instability in the Pathogenesis of Ventilator-Induced Lung Injury

Abstract

With patients who have acute lung injury, respiratory function is routinely evaluated and the treatment may entail choices from various ventilatory strategies. The ventilatory strategies that have been used over the years are being replaced by newer protocols that represent improvements in patient treatment. However, the rationales for the various ventilatory strategies are largely empirical, because the physiology and mechanics of lung inflation are poorly understood. Researchers have proposed competing and contradictory mechanisms of lung inflation at the alveolar level, based on assessments of lung function and discordant descriptions of histological changes during ventilation. We have researched alveolar histophysiology with animal experiments that combined a conventional histological approach with in vivo microscopy to assess alveolar dynamics during normal and disease-state ventilation. Our video and computer analyses document real-time changes of alveolar size and function, often in the same animal and in adjacent areas of the same lung. Our research indicates that, instead of supporting one theory of alveolar mechanics or another, the various behaviors reportedly exhibited by alveoli may be consistent and represent a continuum between normal alveolar function and the alveolar mechanics of acute lung injury.