ASTHMATIC SYMPTOMS, AIRWAY RESPONSIVENESS AND RECOGNITION OF BRONCHOCONSTRICTION

During an epidemiological investigation of asthma in an occupational s etting, 1126 subjects completed a modified Medical Research Council re spiratory questionnaire, then underwent airway responsiveness measurem ents as PD(20)FEV(1) to methacholine. Previous experience of bronchoco nstriction was assessed in the 481 subjects with measurable airway res ponsiveness (PD(20)FEV(1) <6400 g) by asking ''have you ever felt like this before'' at the end of their methacholine challenge tests, i.e. when the subjects were bronchoconstricted by FEV, decrements of at lea st 20%. The responses to this question bore no relationship to the pre viously administered questionnaire responses about wheezing, chest tig htness, coughing, or breathlessness. However, there was an inverse rel ationship with PD(20)FEV(1) measurements (P<0.001), the positive respo nse rate to the question falling from 92% among those with PD(20)FEV(1 ) <50 mu g to 27% among those with PD(20)FEV(1) in the highest measura ble range (3200-6400 mu g). This suggests that airway responsiveness m easurements are a more reliable guide to subjects' previous experience of substantial bronchoconstriction (i.e. asthma) than are the respons es to respiratory questionnaires.