1. Division of Pulmonary, Critical Care, and Sleep Medicine, MedStar Georgetown University Hospital, Washington, District of Columbia;
2. Laboratory for Computational Physiology, Massachusetts Institute of Technology, Cambridge, Massachusetts;
3. Division of Pulmonary, Critical Care and Sleep Medicine, Beth Israel Deaconess Medical Center, Boston, Massachusetts; and
4. Department of Biostatistics, Harvard T.H. Chan School of Public Health, Harvard University, Boston, Massachusetts