Plethysmographic Loops: A Window on the Lung Pathophysiology of COPD Patients.

Plethysmographic alveolar pressure-flow (-) loops contain potentially relevant information about the pathophysiology of chronic obstructive pulmonary disease (COPD), but no quantitative analysis of these loops during spontaneous breathing has ever been performed. The area of the loop's inspiratory () and expiratory portion (), and the difference between the end-expiratory and end-inspiratory alveolar pressure (Δ) were measured in 20 young, 20 elderly healthy subjects, and 130 stable COPD patients. and Δ increased by 55 and 78% from young to elderly subjects, and by 107 and 122% from elderly subjects to COPD patients, reflecting changes in mechanical heterogeneity, lung-units recruitment/derecruitment, and possibly air trapping occurring with aging and/or obstructive disease.