Recovery of Methacholine Responsiveness after End of Exposure in Occupational Asthma
Jean-Luc Malo and
Heberto Ghezzo
Department of Chest Medicine, Hôpital du Sacré-Cur de Montréal, Montreal, Quebec, Canada
Correspondence and requests for reprints should be addressed to Jean-Luc Malo, M.D., Department of Chest Medicine, Hôpital du Sacré-Cur de Montréal, 5400 West Gouin Boulevard, Montreal, PQ, H4J 1C5 Canada. E-mail: malojl{at}meddir.umontreal.ca
Recent data suggest that responsiveness to methacholine continuesto improve 2 and more years after cessation of exposure to agentscausing occupational asthma (OA). The goal of this study wasto characterize further the curve of improvement to methacholineresponsiveness in subjects with OA. Eighty subjects with confirmedOA who had at least two assessments of a provocative concentrationof histamine causing a 20% drop in FEV1 (PC20) and were seenfor at least 2 years after cessation of exposure. The shapeof recovery of PC20 was assessed by CARMA (James K. Lindsey,Liège, Belgium) analysis. Slopes of recovery were comparedin the first 2.5 years in 55 subjects and from 2.5 years untilthe end of observation in 56 subjects. Recovery curves showedprogressive improvements in PC20 significantly influenced bytime lapse since end of exposure, sex, baseline PC20, and FEV1.The slopes of recovery were significantly different from zeroboth for the first 2.5 years after cessation of exposure (0.27± 0.05 SEM natural logarithm of PC20 per year) and later(0.09 ± 0.008 SEM natural logarithm of PC20 per year),with the slope significantly steeper for the first 2.5 years.This study shows that improvement in responsiveness to methacholinecontinues for years after cessation of exposure but that theimprovement is more rapid in the first 2.5 years.
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[Abstract][PDF]
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ur de Montréal, Montreal, Quebec, Canada
