Quantitative analysis of phonatory characteristics of rabbits has been widely neglected. However, preliminary studies established the rabbit larynx as a potential model of human phonation. This study reports quantitative data on phonation using ex vivo rabbit larynx models to achieve more insight into dependencies of three main components of the phonation process, including airflow, vocal fold dynamics, and the acoustic output. Sustained phonation was induced in 11 ex vivo rabbit larynges. For 414 phonatory conditions, vocal fold vibrations, acoustic, and aerodynamic parameters were analyzed as functions of longitudinal vocal fold pre-stress, applied air flow, and glottal closure insufficiency. Dimensions of the vocal folds were measured and histological data were analyzed. Glottal closure characteristics improved for increasing longitudinal pre-stress and applied airflow. For the subglottal pressure signal only the cepstral peak prominence showed dependency on glottal closure. In contrast, vibrational, acoustic, and aerodynamic parameters were found to be highly dependent on the degree of glottal closure: The more complete the glottal closure during phonation, the better the aerodynamic and acoustic characteristics. Hence, complete or at least partial glottal closure appears to enhance acoustic signal quality. Finally, results validate the ex vivo rabbit larynx as an effective model for analyzing the phonatory process.

Standard laryngoscopic imaging techniques provide only limited two-dimensional insights into the vocal fold vibrations not taking the vertical component into account. However, previous experiments have shown a significant vertical component in the vibration of the vocal folds. We present a 3D reconstruction of the entire superior vocal fold surface from 2D high-speed videoendoscopy via stereo triangulation. In a typical camera-laser set-up the structured laser light pattern is projected on the vocal folds and captured at 4000 fps. The measuring device is suitable for in vivo application since the external dimensions of the miniaturized set-up barely exceed the size of a standard rigid laryngoscope. We provide a conservative estimate on the resulting resolution based on the hardware components and point out the possibilities and limitations of the miniaturized camera-laser set-up. In addition to the 3D vocal fold surface, we extended previous approaches with a G2-continuous model of the vocal fold edge. The clinical applicability was successfully established by the reconstruction of visual data acquired from 2D in vivo high-speed recordings of a female and a male subject. We present extracted dynamic parameters like maximum amplitude and velocity in the vertical direction. The additional vertical component reveals deeper insights into the vibratory dynamics of the vocal folds by means of a non-invasive method. The successful miniaturization allows for in vivo application giving access to the most realistic model available and hence enables a comprehensive understanding of the human phonation process.

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Many cases of disturbed voice signals can be attributed to incomplete glottal closure, vocal fold oscillation asymmetries, and aperiodicity. Often these phenomena occur simultaneously and interact with each other, making a systematic, isolated investigation challenging. Therefore, ex vivo porcine experiments were performed which enable direct control of glottal configurations. Different pre-phonatory glottal gap sizes, adduction levels, and flow rates were adjusted. The resulting glottal closure types were identified in a post-processing step. Finally, the acoustic quality, aerodynamic parameters, and the characteristics of vocal fold oscillation were analyzed in reference to the glottal closure types. Results show that complete glottal closure stabilizes the phonation process indicated through a reduced left-right phase asymmetry, increased amplitude and time periodicity, and an increase in the acoustic quality. Although asymmetry and periodicity parameter variation covers only a small range of absolute values, these small variations have a remarkable influence on the acoustic quality. Due to the fact that these parameters cannot be influenced directly, the authors suggest that the (surgical) reduction of the glottal gap seems to be a promising method to stabilize the phonatory process, which has to be confirmed in future studies.