Published ahead of print on April 7, 2004, doi:10.1164/rccm.200312-1749OC Am. J. Respir. Crit. Care Med., Volume 169, Number 12, June 2004, 1304-1307 A more recent version of this article appeared on June 15, 2004
Submitted on December 23, 2003 Recovery of Methacholine Responsiveness After End of Exposure in Occupational AsthmaJean-Luc Malo1* and Heberto Ghezzo11 Department of Chest Medicine, Sacre-Coeur Hospital, Montreal, Quebec, Canada * To whom correspondence should be addressed. E-mail: malojl{at}meddir.umontreal.ca.
Recent data suggest that responsiveness to methacholine continues to improve two and more years after cessation of exposure to agents causing occupational asthma (OA). Aim: Further characterize the curve of improvement to methacholine responsiveness in subjects with OA. Eighty subjects with confirmed OA who had at least two assessments of PC20 and were seen for at least two years after cessation of exposure. The shape of recovery of PC20 was assessed by CARMA analysis. Slopes of recovery were compared in the first 2.5 years in 55 subjects and from 2.5 years until the end of observation in 56 subjects. Recovery curves showed progressive improvements in PC20 significantly influenced by time lapse since end of exposure, sex, baseline PC20 and FEV1. The slopes of recovery were significantly different from zero both for the first 2.5 years after cessation of exposure (0.27±0.05 SEM lnPC20/yr) and later (0.09± 0.008SEM lnPC20/yr), with the slope significantly steeper for the first 2.5 years. This study shows that improvement in responsiveness to methacholine continues for years after cessation of exposure but that the improvement is more rapid in the first 2.5 years. Key words: Occupational diseases; occupational asthma; bronchial diseases, asthma, bronchial hyperresponsiveness
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