This article describes the pathophysiology of the respiratory system after upper abdominal surgery, emphasizing the role of respiratory muscle dysfunction. The history of current techniques to measure respiratory muscle function are reviewed. The authors describe the postoperative pattern of breathing, speculate on the physiologic mechanisms responsible and discuss the data supporting the role of reflexes arising from the abdomen and the shift of neural output to different respiratory muscles. Finally, the authors review the impact of "closed" surgical interventions such as laparoscopic cholecystectomy.