What is the defining characteristic of Chronic Obstructive Pulmonary Disease (COPD) indicated in pulmonary function tests (PFTs)?

The defining characteristic of Chronic Obstructive Pulmonary Disease (COPD) as indicated in pulmonary function tests (PFTs) is irreversible airflow obstruction. COPD is primarily characterized by a chronic reduction in airflow due to airway inflammation and obstruction, which is not fully reversible with bronchodilator therapy. During PFTs, this is demonstrated by a decreased FEV1 (forced expiratory volume in one second) and a decreased FEV1/FVC (forced vital capacity) ratio.

Patients with COPD experience difficulty in exhaling air from their lungs due to constricted or damaged airways, leading to this irreversible component of airflow limitation. This distinctive feature distinguishes COPD from other respiratory disorders like asthma, where airflow obstruction can be partially or fully reversible.

The other characteristics mentioned do not pertain specifically to COPD. Decreased lung volume can be seen in restrictive lung diseases but is not a hallmark of COPD. Elevated sweat chloride levels are typically associated with cystic fibrosis, not COPD. The presence of reticular patterns is more related to interstitial lung diseases and does not define COPD.