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Submitted on: 23 May 1999.
Revised on: 14 June 1999.
Accepted on: 21 July 1999.
___________________BMC Pulmonary Medicine---BMC
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Submitted on: 02 August 2002.
Revised on: 12 September 2002.
Accepted on: 01 November 2002.
___________________BMC Pulmonary Medicine---BMC
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Submitted on: 19 September 2005.
Revised on: 08 November 2005.
Accepted on: 23 December 2005.
___________________BMC Pulmonary Medicine---BMC
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