Investigating the effects of vertical misalignment and stiffness asymmetry on phonation in a synthetic vocal fold model

Blunt force trauma to the larynx can cause significant damage, resulting in displaced laryngeal cartilage fractures. Vertical misalignment of the left or right vocal fold (VF) in the inferior-superior direction and scarring of the VF tissue are common outcomes. The influence of inferior-superior VF displacement and VF scarring on phonation was investigated using synthetic, self-oscillating VF models in a physiologically-representative facility. Acoustic, kinematic, and aerodynamic parameters were assessed as a function of inferior-superior vertical displacement and asymmetric VF stiffness. The combination of vertical misalignment and asymmetric VF tissue stiffness became most prominent when the inferior-superior misalignment of the VFs exceeded the thickness of the medial surface. Only a small degree of stiffness asymmetry was tolerated before VF kinematics and acoustics were significantly degraded. The position of the scarred VF relative to the healthy one also influenced outcomes. If the stiffer VF was positioned inferior to the normal VF, phonatory outcomes were poorer than when it was positioned superior to the normal VF. Measures of shimmer and jitter were more than twice as high, while cepstral peak prominence was 3-5 dB lower.