In severe pulmonary emphysema, lung volume reduction surgery (LVRS) improves pulmonary function over a 2 year period in selected patients. However, the changes in lung function and maximal flow (V'max) occurring immediately postoperatively are not clear and may contribute to the high morbidity observed. In the present study, we used a chronic canine model of upper lobe emphysema to address this question. METHODS: Bilateral upper lobe emphysema was produced by the intrabronchial administration of papain. Measurements were made prior to and immediately after LVRS was performed. A vacuum-assisted surgical system (VALR Surgical System; Spiration; Redmond, WA) that deploys a compression sleeve over portions of the disease tissue was used to produce LVRS. Changes in V'max were interpreted in terms of the wave-speed theory of flow limitation in which a pressure- sensor was placed into the airway to determine the site of limitation and intrabronchial pressures. RESULTS: In the emphysema group, total lung capacity post-emphysema increased to approximately 20% above the pre-emphysema value, while V'max was reduced as compared with a control group. After LVRS, tidal respiratory compliance and V'max decreased, while lung elastic recoil and frictional resistance increased in both the emphysema and control groups as compared to pre-surgery. CONCLUSION: The acute effect of LVRS leads to an impairment in lung mechanical properties. These changes could contribute to ventilatory complications including the difficulty of weaning patients from mechanical ventilation and the mortality observed from this procedure.