Study Objectives:A nasopharyngeal seal of the velopharyngeal port is important during swallowing and speaking. An acoustic leak through an open velopharyngeal port has also been reported as a source for overestimations of acoustic pharyngograms. Quantitative data on the effects of the size of the acoustic leak on the pharyngogram has not been published. The current exploratory in vitro study was designed to measure the effects of increasing sizes of a nasopharyngeal acoustic leak on the pharyngogram.Methods:A plastic cast of the human upper airway constructed from a postmortem anatomic casting without a nasal cavity was used in the study. Acoustic leaks through a velopharyngeal port, created ~9 cm from the mouth, were mimicked using 12 different sizes of an open velopharyngeal port with areas ranging from 7.1 mm2 to 1.54 cm2. Nasal cavities of either 20 mL or 30 mL were attached to the open velopharyngeal port. Acoustic pharyngometry was used to measure the size of the cast and the nasal cavities per each open velopharyngeal port size in terms of cross-sectional areas (CSA1-2) and volume (area under the curve; AUC1-3).Results:The effect of the size of the acoustic leak was statistically significant for all CSAs (P<0.0001) and AUCs (P<0.0001), whereas the effect of the acoustic leak with addition of the nasal cavities was statistically significant only for CSA2 (P<0.0001), AUC2 (P<0.0001), and AUC3 (P<0.0001).Conclusions:An acoustic leak through an open velopharyngeal port created an overestimation of the volume of the upper airways as displayed on the pharyngogram. Even small acoustic leaks seemed to have an effect on the pharyngogram. The main effect of the open velopharyngeal port appeared to occur distal to the acoustic leak and was influenced by both the size of the acoustic leak, and the volume of area being leaked into.