emphysema, obesity, respiratory mechanics, Aged, Body Mass Index, Case-Control Studies, Cross-Sectional Studies, Diaphragm, Female, Forced Expiratory Volume, Functional Residual Capacity, Humans, Iowa, Lung, Male, Middle Aged, Models, Biological, Obesity, Pulmonary Disease, Chronic Obstructive, Respiratory Mechanics, Severity of Illness Index, Texas, Tomography, X-Ray Computed, Total Lung Capacity, Vital Capacity