NORMAL RANGE OF METHACHOLINE RESPONSIVENESS IN RELATION TO PRECHALLENGE PULMONARY-FUNCTION - THE NORMATIVE AGING STUDY

Methacholine airway responsiveness has been observed to be related to prechallenge level of pulmonary function; however, normal ranges of responsiveness for specific levels of lung function have not been reported. We examined methacholine airway responsiveness in relation to level of prechallenge pulmonary function in a sample of 547 middle-aged and elderly men who denied any history of respiratory illness or symptoms and who had normal levels of prechallenge FEV(1) and FEV(1)/FVC ratio. The cumulative dose of methacholine provoking a 20 percent decline in FEV(1) (PD20FEV(1)) was positively correlated with prechallenge FEV(1) percent predicted (Spearman correlation r = 0.35, p < 0.0001). The fifth percentile of PD20FEV(1), chosen as an estimate of the lower limit of the normal range, varied with the level of prechallenge FEV(1). When applied to a larger sample of 838 men with normal pulmonary function, the use of FEV(1)-specific cut-off values to separate ''normal'' from ''abnormal'' PD20FEV(1) did not improve the sensitivity or specificity of methacholine challenge as a test for questionnaire-reported asthma or wheezing. These data provide lower limits of normal PD20FEV(1); however, these FEV(1)-specific lower limits of normal PD20FEV(1) provided no greater sensitivity and specificity for detecting asthma and wheezing than did a single lower limit of normal PD20FEV(1) for all subjects.