Phonatory effects of type I thyroplasty implant shape and depth of medialization in unilateral vocal fold paralysis

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.

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.

Effects of implant and vocal fold stiffness on voice production after medialization laryngoplasty in an MRI-based vocal fold model

Medialization laryngoplasty is one of the primary surgical interventions in the treatment of glottal insufficiency due to vocal fold paralysis, paresis, or atrophy. During the surgery, an implant is laterally inserted into the larynx to medialize the affected vocal fold toward glottal midline, with the goal of improving glottal closure during phonation and voice production efficiency. While implants of different materials and geometry designs have been used, the effect of implant design on the voice outcome remains unclear. In this simulation study, the effect of implant stiffness was investigated in an MRI-based model of the vocal folds after medialization laryngoplasty. The results showed that implant stiffness had a significant impact on the phonation threshold pressure, glottal area waveform, and fundamental frequency, but only small effect on the closed quotient and other acoustic measures of the produced voice. The effect of implant stiffness also exhibited variability, depending on the stiffness conditions of the vocal fold and paraglottic tissues, indicating that individual differences need to be considered during the planning of medialization laryngoplasty.

Numerical and experimental investigations on vocal fold approximation in healthy and simulated unilateral vocal fold paralysis

We have developed a novel surgical/computational model for the investigation of unilateral vocal fold paralysis (UVFP) which will be used to inform future in silico approaches to improve surgical outcomes in type I thyroplasty. Healthy phonation (HP) was achieved using cricothyroid suture approximation on both sides of the larynx to generate symmetrical vocal fold closure. Following high-speed videoendoscopy (HSV) capture, sutures on the right side of the larynx were removed, partially releasing tension unilaterally and generating asymmetric vocal fold closure characteristic of UVFP (sUVFP condition). HSV revealed symmetric vibration in HP, while in sUVFP the sutured side demonstrated a higher frequency (10 - 11%). For the computational model, ex vivo magnetic resonance imaging (MRI) scans were captured at three configurations: non-approximated (NA), HP, and sUVFP. A finite-element method (FEM) model was built, in which cartilage displacements from the MRI images were used to prescribe the adduction and the vocal fold deformation was simulated before the eigenmode calculation. The results showed that the frequency comparison between the two sides were consistent with observations from HSV. This alignment between the surgical and computational models supports the future application of these methods for the investigation of treatment for UVFP.

Effect of Vocal Fold Implant Placement on Depth of Vibration and Vocal Output

OBJECTIVE

Most type 1 thyroplasty implants and some common injectable materials are mechanically stiff. Placing them close to the supple vocal fold mucosa can potentially dampen vibration and adversely impact phonation, yet this effect has not been systematically investigated. This study aims to examine the effect of implant depth on vocal fold vibration and vocal output.

STUDY DESIGN

Computational simulation.

METHODS

Voice production was simulated with a fiber-gel finite element computational model that incorporates a three-layer vocal fold composition (superficial lamina propria, vocal ligament, thyroarytenoid muscle). Implants of various depths were simulated, with a "deeper" or more medial implant positioned closer to the vocal fold mucosa and replacing more muscle elements. Trajectories of surface and within-tissue nodal points during vibration were produced. Outcome measures were the trajectory radii, fundamental frequency (F₀ ), sound pressure level (SPL), and smoothed cepstral peak prominence (CPPS) as a function of implant depth.

RESULTS

Amplitude of vibration at the vocal fold medial surface was reduced by an implant depth of as little as 14% of the total transverse vocal fold depth. Increase in F₀ and decrease in CPPS were noted beyond 30% to 40% implant depth, and SPL decreased beyond 40% to 60% implant depth.

CONCLUSIONS

Commonly used implants can dampen vibration "from a distance," ie, even without being immediately adjacent to vocal fold mucosa. Since implants are typically placed at depths examined in this study, stiff implants likely have a negative vocal impact in a subset of patients. Softer materials may be preferable, especially in bilateral medialization procedures.

LEVEL OF EVIDENCE

N/A Laryngoscope, 130:2192-2198, 2020.

Quantitative Evaluation of the In Vivo Vocal Fold Medial Surface Shape

OBJECTIVES/HYPOTHESIS

Glottal insufficiency is a common clinical problem in otolaryngology and medialization laryngoplasty (ML) procedures remain the primary treatment modality. Although the goal of ML is to restore physiologic glottal posture and achieve optimal phonation, this posture has not been directly measured. In this study, we assessed glottal medial surface contour changes with selective activation of the intrinsic laryngeal muscles (ILMs).

STUDY DESIGN

Basic science study using an in vivo canine hemilarynx model.

METHODS

In an in vivo canine hemilarynx, India ink was used to mark fleshpoints in a grid-like fashion along the medial surface of the vocal fold and ILMs were activated in a graded manner. A right-angled prism provided two views of the medial surface, which were recorded using a high-speed camera and used to reconstruct the 3D posture deformations of the medial surface.

RESULTS

Thyroarytenoid (TA) muscle activation results in initial inferomedial bulging and increased glottal channel thickness and then glottal adduction with a final rectangular glottal channel shape. Lateral cricoarytenoid (LCA) activation closes the posterior glottis but final posture remains slightly convergent. Together, TA + LCA forms a rectangular glottis with an increased glottal vertical thickness. Posterior cricoarytenoid activation results in abduction and a slightly divergent glottis, whereas cricothyroid activation elongates the glottis and reduces the glottal channel vertical thickness.

CONCLUSIONS

A quantitative analysis of in vivo canine vocal fold medial surface upon activation of selective ILMs is provided. This may guide our therapeutic efforts during medialization laryngoplasty, as well as computational modeling of laryngeal physiology.

The effect of vocal fold vertical stiffness variation on voice production

A parametric study was conducted using the numerical technique that coupled a three-dimensional continuum vocal fold model with a one-dimensional Bernoulli flow model to investigate the effect of vocal fold vertical stiffness variation on voice production. Vertical stiffness gradient was defined as the ratio of the inferior-superior stiffness difference to the mean stiffness and was introduced in the cover layer. The results showed that increasing the vertical stiffness gradient would increase the peak flow rate and sound intensity and decrease the open quotient and threshold pressure. The effect was found to be more prominent at low subglottal pressures. The underlying mechanism might be that the reduced stiffness at the superior aspect of the vocal fold would allow a larger lateral displacement and result in a larger vibration. Increasing the vertical stiffness gradient was also found to increase the vertical phase difference and glottal divergent angle during the vocal fold vibration. Meanwhile, increasing the vertical stiffness variation only slightly increased the mean flow rate, which is important to maintaining the speech time between breaths.

Comparison of vocal outcome following two different procedures for immediate RLN reconstruction

The objective of this study was to compare time-dependent improvements in phonatory function and stroboscopic findings following two different procedures for immediate reconstruction of the recurrent laryngeal nerve (RLN) during neck tumor extirpation. Seventeen patients with neck tumors, consisting of advanced thyroid cancer (n = 15), metastatic neck lymph nodes from other malignant lesions (n = 2), underwent resection of the primary lesion and involved RLN. Immediate RLN reconstruction by either: (1) ansa cervicalis nerve (ACN) to RLN anastomosis (n = 8); or (2) placement of the great auricular nerve (GAN) between the cut ends of the RLN (n = 9) was performed from 2000 to 2011. Phonatory function [maximum phonation time, mean airflow rate (MFR), jitter, and shimmer) and stroboscopic findings (regularity, amplitude, and glottal gap) were examined at 1, 6, and 12 months postoperatively. Stroboscopic findings were assessed by two otolaryngologists and one speech pathologist. There were no significant differences in any parameter for either phonatory function or stroboscopic findings between ACN and GAN with the exception of jitter and shimmer, in which ACN was superior to GAN at 1 month postoperatively. All parameters improved significantly between 1 and 12 months postoperatively for both phonatory function and stroboscopic findings (P < 0.05). Either method of immediate RLN reconstruction at the time of neck tumor extirpation (i.e., ACN or GAN) provided both excellent long-term postoperative phonatory function and stroboscopic findings, and there was little difference in vocal outcome between the two procedures.