Asthmatic symptoms, airway responsiveness and recognition of bronchoconstriction

During an epidemiological investigation of asthma in an occupational setting, 1126 subjects completed a modified Medical Research Council respiratory questionnaire, then underwent airway responsiveness measurements as PD20FEV1 to methacholine. Previous experience of bronchoconstriction was assessed in the 481 subjects with measurable airway responsiveness (PD20FEV1 < 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 FEV1 decrements of at least 20%. The responses to this question bore no relationship to the previously administered questionnaire responses about wheezing, chest tightness, coughing, or breathlessness. However, there was an inverse relationship with PD20FEV1 measurements (P < 0.001), the positive response rate to the question falling from 92% among those with PD20FEV1 < 50 micrograms to 27% among those with PD20FEV1 in the highest measurable range (3200-6400 micrograms). This suggests that airway responsiveness measurements are a more reliable guide to subjects' previous experience of substantial bronchoconstriction (i.e. asthma) than are the responses to respiratory questionnaires.