Spirometry was performed at baseline and 12 months after randomization with a Renaissance II
spirometer (Nellcor Puritan Bennett), according to the guidelines of the American Thoracic Society. The peak expiratory flow rate was measured (in liters per minute) twice daily for a period of two weeks at baseline and every six months thereafter with the use of a digitally recording peak flowmeter (Air- Watch, ENACT Health Management Systems, or Simplicity, Nellcor Puritan Bennett), which was modified to mask the results.