- Correspondence to Dr Scott Halpern, Department of Pulmonary, Allergy and Critical Care, University of Pennsylvania Perelman School of Medicine, 724 Blockley Hall, 423 Guardian Drive, Philadelphia, Pennsylvania 19104, USA;
- Received May 18, 2012
- Accepted May 23, 2012
- First published November 23, 2012.
If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.