1. Section of Pulmonary & Critical Care Medicine, University of Oklahoma Health Sciences Center, No. WP1310, 920 Stanton L Young Boulevard, Oklahoma City, OK 73117, USA
2. Dow University of Health Sciences, Mission Road, Karachi 74200, Pakistan
3. Department of Internal Medicine, University of Oklahoma Health Sciences Center, No. WP1310, 920 Stanton L Young Boulevard, Oklahoma City, OK 73117, USA