1. Department of Internal Medicine, Pulmonary Critical Care and Sleep Division, University of Nebraska Medical Center (UNMC), Omaha, NE, USA
2. Department of Internal Medicine, Allergy and Immunology Division, University of Nebraska Medical Center (UNMC), Omaha, NE, USA
3. Department of Pulmonary Medicine, The University of Texas MD Anderson Cancer Center, Houston, TX, USA
4. VA Nebraska Western Iowa Health Care System, Omaha, NE, USA
5. Department of Environmental, Agricultural and Occupational Health, UNMC, Omaha, NE, USA