Singing excised human larynges: Investigating aerodynamical and biomechanical control of phonation
Résumé
The fundamental frequency of the singing voice is controlled by biomechanical and aerodynamical laryngeal parameters. In this ex vivo study, we have independently simulated several of these control parameters, namely subglottal pressure, vocal fold extension and arytenoid compression, using excised human larynges in order to investigate the fluid-structure relationship between subglottal pressure and fundamental frequency. A subglottal supply of compressed air was used to induce vocal fold self-oscillation in one female larynx (96 years) tested directly after dissection (<72 hours post-mortem), and seven frozen larynges (4 female, and 3 male, aged 81±11 and 77±9 years respectively) tested after thawing. Each of the tested control parameters results in a voice with similar dynamic and frequency ranges albeit with a non-linear relationship between subglottal pressure and fundamental frequency, evidenced by pitch jumps and hysteresis. Thus in principle, control of the fundamental frequency of the voice over its entire range can be achieved by using any of the laryngeal parameters in isolation. However, performance of a smooth glissando or a messa di voce would require fine control of multiple parameters “in concert” to dynamically compensate for the non-linearities and avoid pitch jumps.Furthermore, application of a subglottal source of pressurised air causes a narrowing of the aryepiglottic tube due to the Bernoulli force and in many cases self-oscillation of the ventricular and/or aryepiglottic folds occurs unless the supraglottic structure is held separate. Thus, further study is needed to effectively simulate the biomechanical control of the supraglottic laryngeal structures ex vivo.