Lung-volume reduction surgery (LVRS) improves static lung elastic recoil in selected patients with severe chronic obstructive pulmonary disease (COPD). This explains the increase in FEV1 in many COPD patients who undergo LVRS, but fails to explain clinical improvement in those without changes in FEV1. We prospectively evaluated 17 patients after pulmonary rehabilitation but prior to and again at least 3 mo after bilateral LVRS done via median sternotomy. In addition to pulmonary function, lung elastic recoil, walking distance, and exercise capacity, we evaluated static and dynamic respiratory muscle (RM) function, and dyspnea. In 12 patients we also quantified dynamic hyperinflation (end-expiratory and end-inspiratory lung volume [EELV and EILV, respectively]). After LVRS, FEV1 rose from 26.7 +/- 1.8 to 39.0 +/- 3.7% predicted (p < 0.004), whereas TLC dropped from 134.7 +/- 4.8 to 118.3 +/- 4.4% predicted (p < 0.0002), and RV from 239.6 +/- 14.8 to 180.3 +/- 8.7% predicted (p < 0.0002). Isowork dyspnea decreased as assessed with a visual analogue scale (VAS) (79.6 +/- 5.2 versus 49.3 +/- 7.5 mm, p < 0.005) and the Borg scale (7.1 +/- 0.6 versus 3.5 +/- 0.6, p = 0.002). Walking distance improved significantly and, in the 12 patients in whom they were measured, EELV and EILV decreased at rest and at isowork. Maximal transdiaphragmatic pressure rose from 67.1 +/- 8.3 to 92.0 +/- 7.5 cm H2O (p < 0.03). Resting RM function changed little, but at isowork improved significantly after LVRS. Excluding one outlier, there was a strong linear correlation between the change in Borg-scale score at equivalent work loads before and after LVRS and the change in EELV (% predicted TLC, r = 0.75, p < 0.001), as well as between the change in Borg-scale score and the absolute decrease in end-expiratory pleural pressure (Ppl(e)) (r = 0.78, p = 0.004). Successful LVRS improves not only lung recoil, but also respiratory muscle function, and reduces dynamic hyperinflation. These changes help explain the decreased dyspnea and improved exercise capacity seen after LVRS, and add to current understanding of the mechanisms by which this procedure may help selected patients with severe emphysema.