Sulphur dioxide sensitivity and plasma antioxidants in adult subjects with asthma

To screen adult subjects with asthma for sensitivity to inhaled sulphur dioxide (SO2) and identify subject characteristics associated with that sensitivity. Medication use, symptoms, and plasma antioxidant nutrients between SO2 responders and non-responders were compared.

Adult subjects (ages 18-39 years) with asthma were exposed to 0.5 ppm SO2 for 10 minutes during moderate exercise. Pulmonary function tests and symptom ratings were assessed before and after exposure (n = 47). A subject was classified as sensitive to SO2 if forced expiratory volume in 1 second (FEV1) showed a drop > or = 8% over baseline. Blood samples were obtained from subjects (n = 38) before the SO2 challenge; plasma ascorbate, alpha-tocopherol, retinol, carotenoids, and lipids were measured.

Of the 47 subjects screened, 53% had a drop in FEV1 > or = 8% (ranging from -8% to -44%). Among those 25 subjects, the mean drop in FEV1 was -17.2%. Baseline pulmonary function indices (FEV1% of predicted and FEV1/FVC% (forced vital capacity)) did not predict sensitivity to SO2. Although use of medication was inversely related to changes in pulmonary function after SO2 (p < 0.05), both SO2 responders and non-responders were represented in each medication category. Total symptom scores after exposure were significantly correlated with changes in FEV1 (p < 0.05), FVC (p < 0.05), and peak expiratory flow (PEF) (p < 0.01) but not forced expiratory flow between 25% and 75% vital capacity (FEF25-75). Plasma beta-carotene concentrations were inversely associated with PEF values and ascorbate concentrations were inversely associated with FEV1 and FEV1/FVC (p = 0.05 in all cases). High density lipoprotein concentrations were positively correlated with FEV1% of predicted (p < 0.05) and inversely correlated with change in FEF25-75 (p < 0.05) after SO2.

These results show that the response to SO2 among adults with mild to moderate asthma is very diverse. Severity of asthma defined by medication category was not a predictor of sensitivity to SO2. Lung function values were associated with beta-carotene and ascorbate concentrations in plasma; however, plasma antioxidant nutrient concentrations were not associated with sensitivity to inhaled SO2.