EXERCISE INCREASES SULFUR DIOXIDE-INDUCED BRONCHOCONSTRICTION IN ASTHMATIC SUBJECTS

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Abstract
To determine whether moderate exercise modifies the bronchoconstriction produced by the environmental pollutant SO2 in subjects with mild asthma, 7 subjects were studied. Changes in specific airway resistance (SRaw) produced by 10 min of exercise alone (400 kpm[kilopound]/min on a cycle ergometer), inhalation of SO2 alone and the combination of exercise and SO2 were compared. During all studies a subject breathed SO2 and/or air from a mouthpiece. In 6 additional subjects, the increase in SRaw produced by inhalation of SO2 during exercise was compared to that produced by eucapnic hyperventilation with SO2. Neither inhalation of 0.50 ppm of SO2 at rest nor exercise or hyperventilation alone had any effect on SRaw. Inhalation of SO2 during exercise significantly increased SRaw (from 8.46 .+-. 3.58 l .times. cm H2O/l per s (mean .+-. SD) to 18.16 .+-. 10.05 at 0.50 ppm and from 8.07 .+-. 2.69 to 10.48 .+-. 4.49 at 0.25 ppm (P < 0.05)). In the 2 most responsive subjects inhalation of 0.10 ppm of SO2 during exercise also significantly increased SRaw. The SRaw increased by the same amount whether SO2 was inhaled during exercise or during eucapnic hyperventilation at the same minute ventilation, but the time course of the increase in SRaw was different. The SRaw was at or near maximal values at the 1st measurement (30 s) after hyperventilation but not until 2-4 min after exercise. When 4 subjects took larger breaths after inhaling SO2 during eucapnic hyperventilation to more closely match the volume of the breaths taken after exercise, the time courses of SO2-induced bronchoconstriction after hyperventilation and after exercise were nearly identical. Apparently, exercise increases the bronchoconstriction produced by a given concentration of SO2 in subjects with asthma by increasing the minute volume of ventilation. Apparently, the delay in bronchoconstriction after exercise is due to the large tidal volumes that persist for some minutes during recovery.