Differing response of asthmatics to sulfur dioxide exposure with continuous and intermittent exercise

Ten subjects with mild asthma were initially exposed in an environmental chamber (26 degrees C 70% relative humidity) to clean air and 1.0 ppm SO2 while performing 3 sets of 10-min treadmill exercises (ventilation, 41 L/min) broken by 15-min rest periods. To evaluate the effects of the pattern and duration of exercise on the response to SO2 exposure, the subjects were then exposed to the same environmental conditions while exercising continuously for 30 min. Specific airway resistance (SRaw) was measured by body plethysmography before each exposure and after each exercise. All SO2 responses were significantly greater than the clean air responses. With intermittent exercise and SO2 exposure, mean SRaw measurements (preexposure and after 10, 20, and 30 min of exercise) were 5.4, 14.7, 12.8, and 11.1 cm H2O/s. After SO2 exposure with continuous exercise, the mean SRaw showed an increase from 5.2 to 17.3 cm H2O/s. This increase was significantly (p = 0.018) greater than the response after the third exercise in the intermittent protocol. It appears that asthmatics show an attenuated response to repetitive exercise in an atmosphere of 1.00 ppm SO2 and that the response to SO2 exposure develops rapidly and is maintained during 30 min of continuous exercise.