Impact of Vertical Stiffness Gradient on the Maximum Divergence Angle

Abstract

Introduction: During vocal fold vibration, the medial surface of both folds forms a convergent shape during opening and a divergent shape during closing. A greater maximum divergence angle is associated with greater closing forces which will increase the closing speed of the glottis. An increased closing speed results in a greater acoustic intensity and greater vocal efficiency. Indentation testing showed that as the strain increases, the inferior aspect of the folds becomes stiffer than the superior aspect, resulting in the vertical stiffness gradient (VSG). We hypothesize that a reduction of the vertical stiffness gradient will reduce the maximum divergence angle.Methods: Four excised canine larynges were tested. Stress-strain curves of the superior and inferior aspects of the fold in the mid membranous plane of the baseline larynges were taken using the indentation method. Calcium hydroxylapatite (CaHA) crystals were then injected into the superior aspect of the fold. The stress-strain tests were repeated. Particle imaging velocimetry (PIV) of the intraglottal velocity fields was performed in three larynges at different subglottal pressures in the mid coronal plane for the baseline and CaHA-injected larynges.Results: CaHA injection reduced the inferior-superior stiffness gradient in all larynges. The maximal divergence angle was markedly reduced. In some cases, there was not a divergent angle.Discussion: Marked reduction of the vertical stiffness gradient significantly reduces the maximum divergence angle. Clinical implications will be discussed.

An Ex‐vivo Model Examining Acoustics and Aerodynamic Effects Following Medialization With and Without Arytenoid Adduction

“…We observed that at low Psg, when FSV is smaller, the difference in circulation strength, and thus its impact on phonation, is less pronounced than at high Psg. This association between greater VE and stronger FSV was shown in a previous study using the excised canine larynx model 29 …”

“…This association between greater VE and stronger FSV was shown in a previous study using the excised canine larynx model. 29 Clinically, increased VE translates to easier, more sustainable phonation. This reduced efficiency causes increased vocal fatigue, a common complaint of UVFP patients.…”

“…Circulation is a measure of the amount of rotation within an enclosed region of the flow field: Γ ¼ Ð Ð s ω ds, where ω is the vorticity normal to the measurement plane, and s is the area encompassing the vortex. Description of how the closed region around FSV was determined can be found in Farbos de Luzan et al 29 Analyses of acoustic features include VE and cepstrum peak prominence (CPP). VE was calculated as the ratio of the acoustic power to the aerodynamic power, detailed by Schutte.…”

“…Circulation is a measure of the amount of rotation within an enclosed region of the flow field: , where ω is the vorticity normal to the measurement plane, and s is the area encompassing the vortex. Description of how the closed region around FSV was determined can be found in Farbos de Luzan et al 29 …”

Acoustic Screening of the “Wet voice”: Proof of Concept in an ex vivo Canine Laryngeal Model

“…Aerodynamic analysis of the wet larynx has not been conducted previously. During phonation, the glottis shape in the mid‐coronal plane is convergent during opening and divergent during closing 13 . This is caused by a phase delay between the inferior and superior edges of the vocal folds known as a vertical phase difference (VPD).…”