Endoscopic evaluation of dynamic narrowing of the pharynx by the Bernouilli effect producing maneuver in patients with obstructive sleep apnea syndrome

To evaluate the dynamic narrowing of the retropalatal pharynx by the Bernouilli effect producing maneuver (BEPM) in patients with obstructive sleep apnea syndrome (OSAS) with computer-assisted analysis of nasopharyngoscopic images. Endoscopic images of the retropalatal pharynx were obtained and their area was measured by NIH imaging. Because changes in distance between the CCD camera of the nasopharyngoscope and the site of pharyngeal narrowing decreased the measurement reliability, the area of the retropalatal pharynx was divided by the square of the uvula's lateral side length for normalization. We calculated both normalized areas: the pharyngeal narrowing during quiet nasal breathing and that during BEPM, which is a forced inspiration through the nose with the mouth closed. The narrowing rate was then calculated as an index of the pharyngeal dynamics. Nasopharyngoscopy combined with BEPM showed a medial motion of the lateral walls of the pharynx due to the Bernoulli effect, which is an increase in speed and a reduction in pressure of a moving gas passing through a tube constriction. There was a significant correlation between the narrowing rate of the retropalatal pharynx and the apnea index. The decrease in intraluminal pressure at the narrowing combined with the higher atmospheric pressure exercised on the lateral pharyngeal walls would induce the pharyngeal collapse. There was also a significant correlation between the normalized retropalatal are and the apnea index. Nasopharyngoscopy with BEPM suggest that in addition to the static narrowing, the dynamic narrowing of the retropalatal pharynx contributes to the pathophysiology of OSAS. The correlation between the apnea index and both the normalized retropalatal area and the narrowing rate of the retropalatal pharynx due to the Bernoulli effect constitute a quantitative and predictive alternative to the evaluation and understanding of the upper airways changes in OSAS.