Surgical lung volume reduction may improve pulmonary function and dyspnea in advanced pulmonary emphysema. To investigate mechanisms of these beneficial effects we studied breathing patterns before and after surgery. Nineteen patients with diffuse pulmonary emphysema (FEV1 < 35% of predicted, total lung capacity > 130% predicted) were studied within 1 mo before, and 1.5 to 7 mo after thoracoscopic volume reduction. Changes of rib cage and abdominal volumes were monitored with calibrated respiratory inductive plethysmography for 20 to 60 min during natural breathing at rest. Pulmonary function and dyspnea were also assessed. Postoperative tidal volumes, respiratory cycle times, and minute ventilation were not significantly different from preoperative values. The contribution of abdominal volume changes to tidal volumes increased from a mean +/- SD of 43 +/- 17% preoperatively to 58 +/- 14% postoperatively (p = 0.03). The fraction of inspiratory time with abdominal paradoxical motion decreased from 12.3 +/- 8.3% preoperatively to 5.1 +/- 5.1% postoperatively (p = 0.02). The phase shift between rib cage and abdominal motion was reduced postoperatively. Hyperinflation, airway obstruction, and subjective ratings of dyspnea were significantly improved. The better synchronization of rib cage-abdominal motion and the greater contribution of abdominal volume changes to tidal volumes are consistent with a reduction of inspiratory loading and a greater force-generating capacity of the diaphragm after surgery.