Imaging of auto-oscillating vocal folds replicas with left–right level difference due to angular asymmetry

Abstract Vertical level difference due to vertical angular asymmetry (up to 20°) between the normal (right) and tilted (left) vocal fold (VF) is experimentally assessed in the framework of unilateral vocal fold paralysis. The upstream pressure and high-speed vibration imaging for different camera view angles are assessed during steady-state auto-oscillation of three different mechanical VF replicas. A global image-based correlation allows to assess the oscillation frequency independently from the camera view angle. Resulting oscillation frequencies matches the ones obtained from aerodynamic data. Mean vibration cycles obtained from videokymographic line-scans at different positions along the posterior–anterior direction are analysed. Left–right VF displacement phase difference, axis shift and left–right mucosal wave phase difference are identified as essential parameters quantifying angular asymmetry. The influence of the degree of angular asymmetry, scan position and replica is discussed.