LVRS downsizes the hyperinflated lung to a more physiologic size. This makes the diaphragmatic dome move upward and increases the area of muscle apposed to the rib cage. This effect improves maximal ventilator and exercise capacity by optimizing the match between the size of the lungs and the rib cage. LVRS improves global inspiratory muscle strength and the contribution of the diaphragm to inspiratory pressure generation and tidal volume. LVRS is offered to selected patients with severe obstruction, as defined by forced expiratory volume in 1 second (FEV1) between 20" and 45" of the predicted value, hyperinflation greater than 150", and residual volume to total lung capacity ratio (RV/TLC) of more than 60". The operation can be performed as an open or thoracoscopic (video-assisted thoracoscopic surgery [VATS]) procedure and may be done unilaterally or bilaterally or staged bilaterally.