Effect of sulphur dioxide on tracheobronchial clearance at rest and during exercise.

Exposure to pollutants may cause injurious effects by impairing mucociliary transport, one of the lung's most important defences. We have studied the effect of sulphur dioxide (SO2) on tracheobronchial clearance (a) at rest and (b) while exercising, by monitoring lung retention of an inhaled radio-aerosol. Clearance was measured in two sets of conditions. 99mTc-albumen aerosol was inhaled as a bolus in late inspiration under controlled conditions to achieve reproducible deposition in large airways. The studies showed: (1) Clearance was highly reproducible in individuals in repeat control studies. (2) Acute exposure to 5 ppm SO2 showed a small transient speeding of mucociliary clearance at rest. (3) (i) Exercise alone speeded clearance significantly (P less than 0.05). (ii) Exercising in 5 ppm SO2 showed a significant speeding of clearance (P less than 0.05) beyond that found in air breathing exercise controls. (4) Pulmonary function tests showed no significant change except a decrease in flow rate (MMEF) in both (a) and (b) studies (P less than 0.01).