Background:The National Emphysema Treatment Trial studied lung volume reduction surgery (LVRS) for its effects on gas exchange, breathing pattern, and dyspnea during exercise in severe emphysema. Methods: Exercise testing was performed at baseline, and 6, 12, and 24 months. Minute ventilation (V E), tidal volume (VT), carbon dioxide output (V CO 2 ), dyspnea rating, and workload were recorded at rest, 3 min of unloaded pedaling, and maximum exercise. PaO 2 , PaCO 2 , pH, fraction of expired carbon dioxide, and bicarbonate were also collected in some subjects at these time points and each minute of testing. There were 1,218 patients enrolled in the study (