The bronchopulmonary system, like most other organ systems in the body, possesses a significant functional reserve. This is most apparent during exercise, when the pulmonary tidal volume and oxygen consumption can increase by a factor of 10–20 over basal values. Under normal conditions exercise tolerance is limited not by the bronchopulmonary system, but by the cardiovascular system. Respiratory limitation generally is seen only in advanced diseases involving the bronchial system, the lung parenchyma, or the pulmonary vascular system. Exercise limitation due to problems of respiratory mechanics may be presumed to exist when the absolute value of the one-second forced expiratory volume (FEV1) is less than 800 ml [8]. This lower limit must be considered, therefore, when predicting residual postoperative function after pulmonary resection. A vital capacity of approximately 15 ml/kg body weight represents another critical value, with lower values implying, at the least, pulmonary exercise limitation [13].