How does the absence or presence of subglottal medialization affect glottal airflow?

OBJECTIVES Our previous work has shown that the symmetric, smooth, convergent shape of the subglottis reduces turbulent airflow at the glottal entrance. Medialization thyroplasty may alter the glottal shape and is very likely to introduce some degree of glottal asymmetry, which could result in increased turbulence and a reduction in voice quality. This study reports the effects of medializing and not medializing the subglottis in silicone models of human cadaveric larynges. METHODS In experiment 1, silicone models of 4 human cadaveric larynges were created. The subglottis was then completely medialized in all 4 models. Hot-wire anemometry was used to measure velocity and turbulence profiles at the entrance and exit of the subglottis. In experiment 2, 1 model was created to accommodate incremental medialization of the glottis without any medialization of the subglottis. Airflow characteristics were likewise measured. RESULTS In experiment 1, the average maximum turbulence intensity (TI) at the exit of the larynx was less than the TI of incoming tracheal airflow for all 4 larynges. In experiment 2, incremental medialization of the glottis did not affect the TI for medialization up to 35%. However, the TI significantly increased for medialization of 53%. CONCLUSIONS Medialization of the subglottis does not significantly affect the turbulence reduction properties of the subglottis, even though subglottal asymmetry is introduced. On the other hand, large amounts of medialization of the glottis only (with no subglottal medialization) can introduce significant amounts of turbulence.