Background

Chronic obstructive pulmonary disease (COPD) is now the third‑leading cause of death in the United States and burdens more than sixteen million adults. Around 1.2 million of these live with Global Initiative for Chronic Obstructive Lung Disease (GOLD) Stage III disease. Stage III of COPD is defined by a fifty‑to‑seventy‑percent deficit in forced‑expiratory volume that usually calls for continuous or nocturnal oxygen therapy. In patients suffering from GOLD Stage III, even a modest change in cough quality is often the first physiological sign that points to a lower‑airway exacerbation—or worse, a bacterial pneumonia.