Structural and functional characteristics of healthy and injured porcine lungs during deflation: a quantitative CT imaging analysis.

The acute respiratory distress syndrome (ARDS) is characterized by pathologic and heterogeneous alterations in the mechanical properties of lung tissue. Although several techniques exist that allow for assessment of global lung mechanics in health and disease, few techniques allow for quantitative assessment of regional mechanics, which is important for understanding the impact of therapeutic interventions on local structure-function relationships. X-ray computed tomography (CT) is a widely available imaging modality for assessment of regional lung structure, given its high spatial resolution, as well as its ability to provide detailed information on regional anatomic and pathologic features. Quantitative computed tomography (qCT) has evolved into an important tool for assessment of regional and global mechanical changes associated with deranged structure-function relationships in many lung diseases, especially ARDS. The purpose of this study was to determine how specific structural and functional characteristics of the acutely injured lung may be altered, as assessed with various qCT imaging metrics. Such alterations may serve as a template for characterizing the severity of ARDS in patients. We evaluated and compared pressure-volume relationships, distensibility, aeration, tissue texture, and parenchymal deformation in healthy and injured lungs of anesthetized pigs, using volumetric CT images obtained during static breath holds from 30 to 0 cmHO airway pressure. We demonstrate how qCT imaging provides unique insight into structure-function changes associated with acute lung injury, and how such techniques may enhance our understanding of regional and global parenchymal mechanics in patients with ARDS or other forms of lung injury. We noted that quantitative computed tomographic (qCT) imaging has potential applications for assessing the severity of regional injury in the lung by providing detailed information on pressure-volume characteristics, distensibility, aeration, tissue texture, and other structure-function relationships. Such image processing techniques may also be useful for evaluating mechanical derangements associated with acute lung injury, thus enhancing our understanding of pulmonary pathophysiologies associated with regional structural and functional heterogeneity, such as ARDS.