['Emphysema is a chronic disease of the lungs with destruction of terminal alveoli and airway obstruction. Lung volume reduction surgery (LVRS) is being investigated for the treatment of emphysema. Increasing resection volumes with LVRS may lead to worsening of carbon monoxide diffusing capacity (Dlco) despite improvement in compliance and flow. We hypothesized that the pulmonary circulation-related parameters, pulmonary artery pressure (PAP) and diffusing capacity (Dlco), may be used as indicators of the maximally tolerated LVRS resection volume.', 'Emphysema was induced in 55 rabbits by endotracheal nebulization, with either single 15,000-unit (mild emphysema) or three 11,000-unit (moderate emphysema) doses of elastase. At Week 6, bilateral LVRS was performed via median sternotomy with an endoscopic stapler. Single-breath Dlco, static compliance, and PAP were measured prior to emphysema induction, preoperatively, and 1 week following LVRS. Animals were divided into the following groups: Group I (mild emphysema, <3 g resected), group II (mild emphysema, >3 g resected), group III (moderate emphysema, <3 g resected), group IV (moderate emphysema, >3 g resected).', 'All animals having LVRS had immediate postoperative increase in pulmonary vascular resistance (PVR) following lung resection. Mean PAP, however, remained elevated when measured 1 week after LVRS (sacrifice) in animals with moderate emphysema. This is in contrast to animals with mild emphysema, in which follow-up PAPs approached preoperative baseline.'] Do pulmonary vascular pressures increase after lung volume reduction surgery in rabbits with more severe emphysema?