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.
Pierce RJ, Payne CR, Williams SJ, Denison DM, Clark TJ.Pierce RJ, et al. Among authors: clark tj.Chest. 1981 May;79(5):506-11. doi: 10.1378/chest.79.5.506.Chest. 1981.PMID: 7014120Clinical Trial.
Williams SJ, Winner SJ, Clark TJ.Williams SJ, et al. Among authors: clark tj.Thorax. 1981 Aug;36(8):629-31. doi: 10.1136/thx.36.8.629.Thorax. 1981.PMID: 7031975Free PMC article.Clinical Trial.