Soft palate and oronasal breathing in humans.

In 20 naive patients without respiratory impairment, we investigated the ability of the soft palate to direct airflow during breathing. Patients were connected to a spirometer, without noseclip. No instructions were given on the breathing route. During quiet respiration, 15 patients breathed solely through the nose, despite an open mouth. During forced vital capacity (FVC) maneuvers, 19 patients expired exclusively through the mouth. When specifically asked to breathe quietly through the mouth, pure nasal breathing was no longer observed. Tidal volume (VT) or FVC were comparable when patients were asked to breathe through the mouth, with or without noseclip: 0.67 +/- 0.46 vs. 0.60 +/- 0.21 liter for VT (mean +/- SD); 4.05 +/- 0.65 vs. 4.18 +/- 0.70 liters for FVC. In eight separate healthy volunteers, the soft palate was shown by fluoroscopy to close the oropharyngeal isthmus during quiet breathing (resulting in pure nasal breathing) and to close the nasopharynx during FVC efforts (resulting in mouth breathing). During oronasal breathing, the soft palate lay in between the tongue and the posterior pharyngeal wall. These data suggest that when both mouth and nose are open, the soft palate is responsible for the partitioning of oronasal flow.