Acoustics and aerodynamic effects following glottal and infraglottal medialization in an excised larynx model.

OBJECTIVE: This study aimed to investigate the impact of the implant's vertical location during Type 1 Thyroplasty (T1T) on acoustics and glottal aerodynamics using excised canine larynx model, providing insights into the optimal technique for treating unilateral vocal fold paralysis (UVFP). METHODS: Measurements were conducted in six excised canine larynges using Silastic implants. Two implant locations, glottal and infraglottal, were tested for each larynx at low and high subglottal pressure levels. Acoustic and intraglottal flow velocity field measurements were taken to assess vocal efficiency (VE), cepstral peak prominence (CPP), and the development of intraglottal vortices. RESULTS: The results indicated that the implant's vertical location significantly influenced vocal efficiency (p = 0.045), with the infraglottal implant generally yielding higher VE values. The effect on CPP was not statistically significant (p = 0.234). Intraglottal velocity field measurements demonstrated larger glottal divergence angles and stronger vortices with the infraglottal implant. CONCLUSION: The findings suggest that medializing the paralyzed fold at the infraglottal level rather than the glottal level can lead to improved vocal efficiency. The observed larger divergence angles and stronger intraglottal vortices with infraglottal medialization may enhance voice outcomes in UVFP patients. These findings have important implications for optimizing T1T procedures and improving voice quality in individuals with UVFP. Further research is warranted to validate these results in clinical settings.

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

BACKGROUND: Current protocols for bedside swallow evaluation have high rates of false negative results. Though experts are not consistently able to screen for aspiration risk by assessing vocal quality, there is emerging evidence that vocal acoustic parameters are significantly different in patients at risk of aspiration. Herein, we aimed to determine whether the presence of material on the vocal folds in an excised canine laryngeal model may have an impact on acoustic and aerodynamic measures. METHODS: Two ex vivo canine larynges were tested. Three liquids of different viscosities (1:100 diluted glycerin, pure glycerin, and honey-thick Varibar) were placed on the vocal folds at a constant volume. Acoustic and aerodynamic measures were obtained in both adducted and abducted vocal fold configurations. Intraglottal high-speed imaging was used to approximate the maximum divergence angle of the larynges in the studied conditions and examine its relationship to vocal efficiency (VE) and acoustic measures. RESULTS: In glottic insufficiency conditions only, we found that several acoustic parameters could predict the presence of material on the vocal folds. Based on the combination of the aerodynamic and acoustic data, we found that decreased spectral energy in the higher harmonics was associated with decreased VE in the presence of material on the vocal folds and/or glottic insufficiency. CONCLUSION: Decreased spectral energy in the higher harmonics of the voice was found to be a potential biomarker of swallowing dysfunction, as it correlates with decreased vocal efficiency due to material on the vocal folds and/or glottic insufficiency, both of which are known risk factors for aspiration. LEVEL OF EVIDENCE: NA Laryngoscope, 133:2517-2524, 2023.

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

OBJECTIVES/HYPOTHESIS: Quantify differences in acoustics and intraglottal flow fields between Thyroplasty Type 1 (TT1) with and without arytenoid adduction (AA) using excised canine larynx model. STUDY DESIGN: Basic science experiments using excised larynges. METHODS: Surgical procedures were implemented in eight excised canine larynges. Acoustics and intraglottal flow measurements were taken at low and high subglottal pressures in each experimental setup. RESULTS: In all larynges, vocal efficiency (VE) and cepstrum peak prominence (CPP) were higher, and the mean phonatory flow rate was lower in TT1 with AA than without AA. The glottal asymmetry is reduced with AA and promotes the formation of stronger vortices in the glottal flow during the closing phase of the vibrating folds. CONCLUSIONS: Findings suggest a clear acoustic and aerodynamic benefit to the addition of AA when performing TT1. It shows significant improvement in CPP, translating to decreased breathiness and dysphonia and increased VE, leading to easier and more sustainable phonation. Stronger intraglottal vortices are known to be correlated with the loudness of voice produced by phonation. LEVEL OF EVIDENCE: N/A Laryngoscope, 133:621-627, 2023.

Impact of Vertical Stiffness Gradient on the Maximum Divergence Angle.

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. LEVEL OF EVIDENCE: NA Laryngoscope, 131:E1934-E1940, 2021.

Experimental study of a lenticular jet.

Non-circular jets, particularly elongated jets and jets with sharp corners, are of interest due to their enhanced large- and small-scale mixing and combustion stability. Non-circular jet geometries such as elliptic, triangular, rectangular, and square have been extensively studied. The non-uniform curvature and elongated design of elliptic and rectangular jets has been shown to facilitate axis switching. Additionally, jets with sharp corners have been shown to facilitate small-scale mixing and further vortex ring deformation, as has been observed in triangular, square, and rectangular jets. There are, however, currently no data on the flow characteristics of a jet that combines these two features, i.e., it enhances both large- and small-scale mixing. The jet is issuing from a nozzle shape defined by two arcs of a circle connecting at sharp corners in the shape of an eye (hereafter termed 'lenticular'). The current study uses experimental techniques to characterize the lenticular jet and compare its behavior to previously studied circular and non-circular jets. Additionally, snapshot POD analysis was used to identify coherent structures and their dynamic features. The lenticular jet was found to have higher entrainment and stronger mixing than a traditional round jet, and comparable mixing and entrainment characteristics as previously studied non-circular jet geometries. It is particularly interesting to compare the jet behavior of the lenticular jet to an elliptic jet. The geometry of these two jets is extremely similar, the difference being sharp corners along the major axis of the lenticular jet. By comparing the lenticular jet and the elliptic jet, the effect of sharp corners, which have been shown to increase small-scale mixing and vortex ring deformation, can be observed. It was found that along the minor axis, where geometry was similar, shear layer turbulence intensity and spreading rate of the jets were also similar. Along the major axis, however, introducing corner features in the lenticular jet lowered the spread rate, resulted in a faster breakdown of turbulence in the shear layer, increased exit turbulence, and resulted in anisotropic centerline turbulence.

Volume velocity in a canine larynx model using time­resolved tomographic particle image velocimetry.

In the classic source-filter theory, the source of sound is flow modulation. "Flow" is the flow rate (Q) and flow modulation is dQ/dt. Other investigators have argued, using theoretical, computational, and mechanical models of the larynx, that there are additional sources of sound. To determine the acoustic role of dQ/dt in a tissue model, Q needs to be accurately measured within a few millimeters of the glottal exit; however, no direct measures of Q currently exist. The goal of this study is to obtain this waveform in an excised canine larynx model using time-resolved tomographic particle image velocimetry. The flow rate data are captured simultaneously with acoustic measurements to determine relations with vocal characteristics. The results show that glottal waveform characteristics such as maximum flow declination rate are proportional to the subglottal pressure, fundamental frequency, and acoustic intensity. These findings are important as they use direct measurements of the volume flow at the glottal exit to validate some of the assumptions used in the source-filter theory. In addition, future work will address the accuracy of indirect clinical measurement techniques, such as the Rothenberg mask.