1. Pulmonology Division, Department of Internal Medicine, St. Mary's Hospital, Catholic University College of Medicine, Seoul 150-713, Korea.
2. Pulmonology Division, Department of Internal Medicine, Seoul St. Mary's Hospital, Catholic University College of Medicine, Seoul 137-701, Korea.
3. Pulmonology Division, Department of Internal Medicine, Eui Jung Bu St. Mary's Hospital, Catholic University College of Medicine, Uijeongbu 480-717, Korea.
4. Pulmonology Division, St. Paul's Hospital, Catholic University College of Medicine, Seoul 130-709, Korea.