Evidence for passing down of postnasal drip into respiratory organs

Postnasal drip is believed to be one of the main sources of serious respiratory diseases, such as sinobronchial syndrome. However, there is little direct evidence showing that postnasal drip flows into the trachea and results in the development of inflammatory responses in the lower airway. In the present study, whether postnasal drip entered the respiratory organs and whether material in the trachea moved toward the lungs and the digestive organs were examined by using an experimental model with mice.

In the first set of experiments, 1.0 microL of 51Cr-labeled pseudo-postnasal drip in a normal saline or a glycerin solution was instilled into the nasal cavity of male ICR mice anesthetized with sodium barbital by intraperitoneal injection. In the second set of experiments, the destination of 51Cr-labeled red blood cells (RBCs) after intratracheal instillation was examined in the anesthetized mice. The lungs, the stomach and the intestines were removed from mice killed under anesthesia at various intervals after instillation, and measured for radioactivity.

When glycerin solution containing 51Cr (but not normal saline) was instilled in mice, the presence of much higher levels of 51Cr was observed in the lungs. Although the presence of high levels of 51Cr-labeled RBCs was observed in the lungs one hour after instillation radioactivity in the lungs gradually decreased as time went by. On the other hand, radioactivity in the digestive organs gradually increased and peaked three hours after instillation with 51Cr-labeled RBC.

These results suggest that thicker viscous postnasal drip can flow into the respiratory organs when the host is asleep. In addition, postnasal drip which flows into the trachea can move gradually to the oral side by mucociliary transportation of the tracheal mucosa and thus be swallowed.