Magnitude of the interaction between the bronchomotor effects of sulfur dioxide and those of dry (cold) air.

We studied the interaction between airway drying (cooling) and inhalation of sulfur dioxide (SO2) causing bronchoconstriction in 8 subjects with mild asthma. On 3 separate days, we measured specific airway resistance (SRaw) before and after the subject performed voluntary eucapnic hyperpnea at a constant minute ventilation (30 to 40 L/min) for successive 3-min periods with doubling concentrations of SO2 in dry cold air (-20 degrees C, 0% relative humidity), in dry warm air (22 degrees C, 0% relative humidity), and in partially humidified warm air (22 degrees C, 70% relative humidity). On another day, we measured SRaw before and after the subject performed each of 6 successive 3-min periods of voluntary eucapnic hyperpnea at the same minute ventilation breathing dry cold air without SO2. The concentration of SO2 that caused a 100% increase in SRaw was significantly lower in dry cold air and in dry warm air than it was in humidified warm air. Repeated hyperpnea with dry cold air without SO2 at the same ventilation had no effect on SRaw. We then had the same subjects perform voluntary eucapnic hyperpnea at successively increasing levels of ventilation on 3 different days with dry air alone, dry air with 0.1 ppm SO2, or dry air with 0.25 ppm SO2. The minute ventilation that caused an 80% increase in SRaw was significantly lower for hyperpnea with 0.1 and with 0.25 ppm SO2 than for dry air without SO2, but these differences were small.(ABSTRACT TRUNCATED AT 250 WORDS)