FACTORS INFLUENCING THE OCCURRENCE OF AIRWAY HYPERREACTIVITY IN THE GENERAL-POPULATION - THE IMPORTANCE OF ATOPY AND AIRWAY CALIBER

The factors that determine the occurrence of airway hyperreactivity in the general population are not clearly understood. This study was des igned to assess the independent effects of age, atopy, smoking and air way calibre. In a random sample of 2,415 adults aged 18-70 yrs we meas ured reactivity to methacholine as the dose provoking a 20% fall (PD20 ) in one-second forced expiratory volume (FEV(1)), atopy as the mean s kin wheal response to three common environmental allergens, and airway calibre as the baseline FEV(1) in absolute terms, as percent predicte d (FEV(1) % predicted) and as percent forced vital capacity (FEV(1) % FVC). Hyperreactivity, defined as a PD(20)less than or equal to 12.25 mu mol, was present in 314 (13%) of the sample, and before adjustment for FEV(1) was more common in females (independent odds ratio (OR)=2.0 5 (95% confidence interval 1.6-2.7)), current smokers (OR=1.89 (1.3-2. 6)), atopics (OR=1.39 (1.3-1.5) per mm skin wheal), and in older age g roups (OR for age 60-70 yrs relative to 18-29 yrs =2.70 (1.7-4.3)). Ho wever, the odds of hyperreactivity were also strongly and independentl y related to absolute FEV(1) (OR=0.46 (0.27-0.77) per litre), FEV(1) % predicted (OR=0.96 (0.94-0.98) per percent), and FEV(1) % FVC (OR=0.9 2 (0.90-0.94) per percent; combined chi-square on 3 df =312, p<<0.0001 ). After adjustment for these effects, the independent association wit h atopy remained unchanged but the effects of sex and smoking were no longer independently significant whilst the effect of age was modified such that increased age was associated with a significantly lower rat her than a higher risk of hyperreactivity. These findings demonstrate that at any given age, atopy and airway calibre are the major determin ants of hyperreactivity in the general population.