INTERACTION OF SULFUR-DIOXIDE AND DRY COLD AIR IN CAUSING BRONCHOCONSTRICTION IN ASTHMATIC SUBJECTS

To determine whether SO2 and airway cooling and drying interact in causing bronchoconstriction in persons who have asthma, specific airway resistance was measured in 7 asthmatic subjects before and after they performed voluntary eucapnic hyperpnea for 3 min breathing 4 different gas mixtures. The mixtures, which the subjects breathed through a mouthpiece in random order on 4 different days, were humidified room-temperature air, humidified room-temperature air containing 0.5 ppm SO2, cold dry air and cold dry air containing 0.5 ppm SO2. Each subject breathed at a rate and depth known from preliminary studies to cause little or no bronchoconstriction when the subject inhaled 0.5 ppm SO2 in humidified room-temperature air or cold dry air. When given independently in the blinded study, 0.5 ppm SO2 or cold dry air again caused insignificant bronchoconstriction, but when given togheter the 2 stimuli caused significant bronchoconstriction, as indicated by an increase in specific airway resistance from 6.94 .+-. 2.85 to 22.35 .+-. 10.28 l .cntdot. cmH2O .cntdot. l-1 .cntdot. s (mean .+-. SD) (P < 0.001) Thus, airway cooling and/or drying increases the bronchoconstriction induced by inhaled SO2 in persons who have asthma. This increase suggests that persons who have asthma may be more sensitive to the bronchconstrictor effects of ambient SO2 in cold dry environments than in warm moist environments.