Estimating subglottal pressure using incomplete airflow interruption

Objective/Hypothesis. Subglottal pressure (SGP) measurements are often used to assess laryngeal function; however, current methods to measure SGP are invasive or do not estimate SGP during phonation. The purpose of this study was to devise a noninvasive technique to estimate SGP without interrupting phonation. Study Design: This was a methodologic study designed to calculate the SGP of a human subject. Methods: A new technique to estimate SGP was developed in which subject airflow was partially interrupted by introducing two different impedances (pneumatic resistors) through a balloon valve controlled mouthpiece. The changes in airflow across varying impedances were used to estimate SGP in human subjects based on the predictable relationships between SGP, impedance, and airflow measurements. The technique was used to assess eight human subjects (age 19-30) phonating at intensities of 65, 72, and 80 dB. Results: The estimated SGP from the human subjects fell within a range (5.52-8.91 cm H2O) that was consistent with previous studies. As other studies have found, SGP estimations significantly increased as subjects phonated at greater intensities (P<.01). Intrasubject standard deviations compared favorably with those from previous studies of complete airflow interruption, suggesting satisfactory reliability. The technique was validated using a mechanical "pseudolung" device (r(2)=0.9982). Conclusions: Incomplete airflow interruption offers the potential for useful clinical application to assess the severity of vocal pathology by estimating SGP during continuous phonation.