Site and Mechanism(s) of Expiratory Airflow Limitation in COPD, Emphysema and Asthma-COPD Overlap

The purpose of this cross-sectional, observational study is to evaluate the site and mechanism(s) for expiratory airflow limitation in chronic, treated, current or former smokers (\>15 pack years) with COPD, Emphysema, and Asthma-COPD Overlap with mild to severe expiratory airflow limitation. Treatment may include short and long acting inhaled beta2agonists, short and long acting inhaled muscarinic receptor antagonists, inhaled and or oral corticosteroid, oral antibiotic, supplemental oxygen, and PDE type 4 inhibitor. In some cases, the patient may have had a history of asthma preceding the development of COPD (Asthma COPD Overlap).

The investigators are interested in determining the predominant site of expiratory airflow limitation including large central airways vs small peripheral airways/alveoli. In mild to moderate obstructive airways disease and emphysema, I believe routine spirometry including FEV 1(L), FVC (L), and FEV 1/FVC % may be normal, despite expiratory airflow limitation in lung peripheral airways. I also want to determine whether the mechanism(s) of expiratory airflow limitation are related to measured loss of lung elastic recoil or intrinsic obstruction of small peripheral airways or both. It is also important to determine the extent and distribution of emphysema using high resolution, thin section lung CT with voxel quantification. If available pathological analysis of lung surgical specimens and also formalin inflated lungs obtained at autopsy will also be studied. Blood studies will include but not limited to CBC, serum IgE, complete metabolic panel, and alpha 1 antitrypsin levels. Extensive lung function testing will also include spirometry tests before and after inhaled albuterol bronchodilation, lung volumes measured in a plethysmograph, diffusing capacity, measurement of lung elasticity that requires placement of an esophageal balloon, measurement of airflow after breathing a mixture of 80% helium-20%oxygen for 7-10 minutes, and measurements of exhaled nitric oxide. CAT scans of the lungs will be obtained to evaluate the presence, extent and distribution of emphysema and bronchiectasis. In some cases, bronchoscopy may be requested. The above tests may be uncomfortable but should cause no harm.