Inhalation route effects on exposure to 2.0 parts per million sulfur dioxide in normal subjects

A number of investigations have attributed the control of the nasal to oral/nasal ventilation transition to nasal resistance. To investigate possible changes in nasal resistance due to sulfur dioxide (SO2) exposure, 14 subjects (7 men and 7 women), healthy non-smokers, between the ages of 20 and 46 years, were exposed for 30 minutes to filtered air while free breathing and to 2.0 ppm SO2 with either free breathing, forced oral or forced nasal breathing with continuous exercise at a workload 300 kg.m/min below the workload which initiated cross-over from nasal to oral/nasal breathing in a preliminary incremental workload test. An incremental work test under the ambient conditions was performed immediately following the 30-minute exercise to ascertain any change in the cross-over ventilation. Pre- and post-measures of pulmonary functions were obtained to ascertain any changes in these parameters due to the exposure. There was a significant difference in the workload at which cross-over occurred following forced oral breathing in 2.0 ppm sulfur dioxide. The nasal ventilation prior to cross-over and the nasal component of ventilation were significantly smaller for this exposure condition, indicating a possible change in nasal dynamics following the 30 minutes of forced oral breathing in 2.0 ppm SO2. Lack of concomitant changes in pulmonary function tests including airway resistance suggests that breathing 2.0 ppm SO2 does not affect normal subjects whether administration is by free, forced oral or forced nasal breathing.