An official website of the United States government
The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before
sharing sensitive information, make sure you’re on a federal
government site.
The site is secure.
The https:// ensures that you are connecting to the
official website and that any information you provide is encrypted
and transmitted securely.
Clarke DE, Raffin TA.Clarke DE, et al. Among authors: raffin ta.Chest. 1990 Apr;97(4):966-72. doi: 10.1378/chest.97.4.966.Chest. 1990.PMID: 2182303Free article.Review.