 There are two commonly used methods to remove chest tubes following thoracotomy. One is to remove the chest tube at maximum inspiration, patient is asked to take a deep breath in and hold it, and the other is to pull the chest tube at maximum expiration,patient is asked to blow out as much air as they can can and hold it. There has been considerable discussion among Thoracic surgeons that one of these two methods may decrease the risk of pneumothorax, the most common complication associated with chest tube removal. The investigators will compare the two methods, and also identify risk factors of developing pneumothorax during chest tube removal. 