[1] Mayo Clin, Div Pulm & Crit Care Med, Dept Med, Rochester, MN 55905 USA
[2] Univ Pittsburgh, Sch Med, Dept Med, Div Gen Internal Med, Pittsburgh, PA USA
[3] Univ Pittsburgh, Grad Sch Publ Hlth, Dept Biostat, Pittsburgh, PA 15261 USA
[4] Univ Calif Los Angeles, Dept Hlth Serv, Los Angeles, CA USA
[5] Univ Calif San Diego, Dept Med & Family & Prevent Med, San Diego, CA 92103 USA
[6] Univ Michigan, Div Pulm & Crit Care Med, Ann Arbor, MI 48109 USA
[7] Johns Hopkins Univ, Div Pulm & Crit Care Med, Baltimore, MD USA
[8] Natl Jewish Med Ctr & Res Ctr, Div Pulm Sci, Denver, CO USA
[9] Univ Pittsburgh, Sch Med, Dept Med, Div Pulm & Crit Care Med, Pittsburgh, PA USA