Increasing Hypoxemia and Dyspnea in Mild Chronic Obstructive Pulmonary Disease

A man with a 3-year history of chronic obstructive pulmonary disease presented with increasing dyspnea on exertion, requiring increasing flow rates of oxygen. He was a former smoker with a 50–pack-year history. He had been diagnosed with stage I low-grade prostate cancer several years previously. Lung examination showed no wheezing. Cardiac examination showed a prominent pulmonary component (P2) of the second heart sound. Noncontrast computed tomography of the chest was unremarkable