Airway responses to sulfur dioxide and methacholine in asthmatics

Sulfur dioxide (SO₂) is a common air pollutant found in the workplace. Considerable variation exists in the airway responses of asthmatics to the inhalation of SO₂. To determine if such variation among asthmatics is related to nonspecific airway reactivity, we compared the threshold doses of methacholine and SO₂ required to produce significant changes in flow rates at 60% of the vital capacity below total lung capacity on the partial expiratory flow volume curve in a group of eight mildly asthmatic subjects. A significant correlation between the dose of SO₂ and the dose of methacholine required to produce bronchocon-striction (r=.86, p<.05) was observed, suggesting that there is a relationship between the response to SO₂ and the response to methacholine in mildly asthmatic individuals. More generally, nonspecific airway hyperreactivity may help to predict untoward airway responses to inhaled SO₂ in the workplace.