The sequence of events that predispose to the onset of sinusitis are usually attributed to pathophysiologic factors within the ostiomeatal complex. Ostial compromise or obstruction with reduced clearance of antral pathogens has been implicated as a major factor that contributes to early sinus disease. Recent work in this laboratory has indicated that other processes may also contribute to this cascade. Using an infectious model in rabbits, the role of nasal obstruction in early, acute sinusitis was studied. Unilateral nasal closure was followed by bilateral inoculation with 10(8) CFU of Streptococcus pneumoniae type 3. Antral gas composition was examined on days 1, 2, 3, 5, 7, and 14, and swabs obtained for culture. Representative rabbits underwent CT scans to evaluate changes in nasal and sinus mucosa. Results showed a significant increase in CO2 and a trend toward a decrease in O2 on the obstructed side. There was also a significant decrease in obstructed CO2 levels from postoperative days (POD) 1-14. Acute sinusitis was not observed in any animal: however, nasal obstruction gave rise to a dramatic prolongation of bacterial retention. On days 2-7 bacteria was consistently cultured from the obstructed side only. CT scans on POD 2 and POD 3 showed mucosal thickening in the sinus and infundibulum on the obstructed side, indicative of sinus pathology. These results indicate that nasal obstruction may be a key factor in the cascade of events that predispose to the onset of sinus disease.