Anatomy and Physiology of the Larynx

Laryngeal Surgery as It Pertains to the Thoracic Surgeon

A surgeon managing complex airway disease benefits from knowledge of laryngeal physiology and pathology. The Larynx provides phonation and protection for the lower airway via closure and cough reflex. Disruption of these functions or development of paralysis or stenosis can lead to respiratory failure. Management includes a variety of endoscopic and open management techniques. Understanding of laryngeal physiology can also limit laryngeal functional impairment through careful preservation of motor nerves and early recognition of injuries.

Computational Study of the Impact of Dehydration-Induced Vocal Fold Stiffness Changes on Voice Production

OBJECTIVE

Systemic vocal fold dehydration is known to increase vocal fold stiffness, which has been hypothesized to have important effect on voice production. However, it remains unclear whether the dehydration-induced vocal fold stiffness changes can have a noticeable impact on phonation, particularly in normal phonation conditions. The goal of this study was to investigate the impact of vocal fold stiffness changes due to vocal fold systemic dehydration and its significance in daily communication.

METHODS

Parametric computational simulation using a three-dimensional vocal fold model, in which the vocal fold stiffness was varied as a function of systemic dehydration levels based on previously-reported experimental data.

RESULTS

The results showed that systemic dehydration had significant effects on voice production only at high levels of dehydration, at which dehydration increased the phonation threshold pressure and fundamental frequency, and decreased glottal opening area, vocal intensity and glottal efficiency. The effect depended mainly on the overall dehydration level but was also slightly affected by the dehydration distribution and muscular control. However, for dehydration levels typical of normal phonation conditions, the effect was negligible.

CONCLUSIONS

The results indicated that dehydration-induced vocal fold stiffness change likely is not an important mechanism through which vocal fold systemic dehydration affects voice production. Nevertheless, a large decrease in glottal efficiency implies a possible perceived increase of vocal effort under a realistic dehydration condition.

A novel technique of voice-sparing cricotracheal resection

Background

Cricotracheal resection (CTR) is considered the standard of care for patients suffering from idiopathic subglottic stenosis (iSGS). Although CTR results in permanent restoration of airway patency, it has a mild to moderate impact on voice quality. Here we propose modifications of the standard CTR technique to make it a voice-preserving procedure.

Methods

Five women with iSGS underwent voice-sparing CTR between January 2022 and January 2023. In this procedure, through several technical adaptations, the function of the cricothyroid joint was preserved. Outcomes of these voice-sparing CTRs were compared to outcomes in patients who underwent standard CTR in our institution. All patients underwent full functional preoperative and postoperative workups, including spirometry, voice measurements, patient self-assessment, and fiberoptic endoscopic evaluation of swallowing.

Results

All 5 patients in the study group suffered from iSGS with high-grade Myer-Cotton III° stenosis (100%); 1 patient had previously undergone endoscopic laser resection. Voice evaluation demonstrated a nearly unchanged fundamental pitch (mean preoperative, 191 ± 73.1 Hz; postoperative, 182 ± 64.2 Hz) and dynamic voice range (preoperative, 24.4 semitones; postoperative, 20.4 semitones). This was in contrast to the control group, in which significantly reduced voice quality was observed.

Conclusions

In selected patients suffering from iSGS, excellent functional results can be obtained with voice-sparing CTR.

The Efficacy of the NHS Waterpipe in Superficial Hydration for People With Healthy Voices: Effects on Acoustic Voice Quality, Phonation Threshold Pressure and Subjective Sensations

OBJECTIVES

This study examined the efficacy of the NHS waterpipe as a superficial hydration treatment in voice production in healthy young women.

STUDY DESIGN

This is a prospective, single-blind, within- and between-subject experimental design.

METHODS

Thirty six female university students (mean age 24.6 years, range 19-45 years) were recruited to the study. Participants were randomized to two experimental groups (E1 and E2) and a control group. E1 underwent hydration treatment with the NHS waterpipe filled with 0.9% saline that was immersed in a cup of heated water. E2 underwent a similar treatment but without heated immersion. The control group received no treatment. Acoustic Voice Quality Index (AVQI v03.01) and its subparameters, phonation threshold pressure, self-perceived phonatory effort and sensation of throat dryness was measured at three time points (before the intervention and immediately and 15 minutes after it).

RESULTS

The Tilt of the AVQI's subparameters increased significantly in the E1 (P = 0.027) and E2 groups (P = 0.027) after the intervention. Furthermore, the E1 group had significantly lower harmonics-to-noise-ratio values at the third measurement point compared to the E2 group (P = 0.023). These findings may result from fluid transported to the vocal fold level. The sensations of throat dryness decreased in the E1 (P = 0.001) and E2 groups (P < 0.0005) after the intervention. Perceived phonatory effort decreased statistically significantly at the final measurement point in the E1 (P = 0.002) and E2 (P = 0.031) groups. No variables changed in the control group.

CONCLUSIONS

The waterpipe seems to be efficient in hydrating vocal folds on single use. It seems to be more efficient when employed with a hot water bath, albeit slightly impairing some acoustic values in the short term. Without the heated fluid, it still seems to decrease sensations of throat dryness and affect acoustic voice quality. The waterpipe does not seem to have an effect on phonation threshold pressure, and it seems to lower self-perceived effort just as efficiently whether the waterpipe is employed using a hot water bath or not. Further research is needed to prove the efficacy of long-term usage and usage with voice patients.

Validity and Reliability of the Arabic Version of the Glottal Function Index in Dysphonic Patients

OBJECTIVES/HYPOTHESIS

The Glottal Function Index (GFI) is a four-item self-administered survey suitable for the evaluation and treatment of patients with glottal dysfunction. To date, it has been translated into Lithuanian, Persian, and Hebrew. This study is intended to translate and cross-culturally adapt the GFI for use in Arabic-speaking patients with dysphonia.

STUDY DESIGN

This work is a cross-sectional study involving the administration of the GFI to participants with dysphonia (cases) and patients without dysphonia (controls). The validation process included reliability and validity assessments.

METHODS

The GFI was translated using forward and backward translation methods from English into Arabic. The questionnaire's reliability was assessed using Cronbach's alpha and test-retest reliability (intraclass correlation coefficient, ICC). The Mann-Whitney test evaluated validity by comparing cases and controls. Finally, the Kruskal-Wallis test examined differences in the GFI across various pathologies.

RESULTS

The GFI demonstrated favorable internal consistency (Cronbach's alpha = 0.848) and excellent test-retest reliability (ICC = 0.993). Significant differences in the A-GFI score between the cases and controls were also observed (P < 0.001), supporting the instrument's validity. However, no statistically significant differences were found in A-GFI across different diagnoses (P = 0.712).

CONCLUSIONS

The A-GFI is a valid and reliable screening tool for clinicians to assess dysphonia and voice impairment in patients in Arabic-speaking countries. The tool is easy to administer in daily clinical practice given its brevity and self-administration.

Temporal expression of Laminin-111 in the developing rat larynx

Laminin-111 is a basement membrane protein that participates in motor innervation and reinnervation. During axonal pathfinding, laminin-111 interacts with netrin-1 (NTN1) and changes its attractant growth cone properties into repulsion. While previous models of recurrent laryngeal nerve (RLN) transection show increased Laminin-111 and NTN1 production after injury, developmental expression in the larynx has not been defined. This study investigates the expression of laminin-111 in laryngeal muscles during primary laryngeal innervation of Sprague Dawley rats. Adult larynges and embryos were sectioned for immunohistochemistry with βIII-Tubulin, laminin subunit α-1 (LAMA1), NTN1, and α-bungarotoxin. Sections were processed for single-molecule inexpensive RNA fluorescence in situ hybridization analysis of LAMA1 mRNA. LAMA1 expression increased in all intrinsic laryngeal muscles, except the medial thyroarytenoid (MTA), at E20.5. At E20.5 there was increased expression in the lateral thyroarytenoid (LTA) and posterior cricoarytenoid (PCA) compared to the MTA. NTN1 upregulation was limited to the LTA and lateral cricoarytenoid (LCA) at E16.5 without any increase in the MTA or PCA. LAMA1 and NTN1 expression did not strictly follow expected patterns relative to the known timing of innervation and does not appear to be acting similarly to its role following RLN injury. These differences between developmental and post-injury innervation provide targets for investigations of therapeutics after nerve injury.

Msx1 haploinsufficiency modifies the Pax9-deficient cardiovascular phenotype

BACKGROUND

Successful embryogenesis relies on the coordinated interaction between genes and tissues. The transcription factors Pax9 and Msx1 genetically interact during mouse craniofacial morphogenesis, and mice deficient for either gene display abnormal tooth and palate development. Pax9 is expressed specifically in the pharyngeal endoderm at mid-embryogenesis, and mice deficient for Pax9 on a C57Bl/6 genetic background also have cardiovascular defects affecting the outflow tract and aortic arch arteries giving double-outlet right ventricle, absent common carotid arteries and interruption of the aortic arch.

RESULTS

In this study we have investigated both the effect of a different genetic background and Msx1 haploinsufficiency on the presentation of the Pax9-deficient cardiovascular phenotype. Compared to mice on a C57Bl/6 background, congenic CD1-Pax9^-/- mice displayed a significantly reduced incidence of outflow tract defects but aortic arch defects were unchanged. Pax9^-/- mice with Msx1 haploinsufficiency, however, have a reduced incidence of interrupted aortic arch, but more cases with cervical origins of the right subclavian artery and aortic arch, than seen in Pax9^-/- mice. This alteration in arch artery defects was accompanied by a rescue in third pharyngeal arch neural crest cell migration and smooth muscle cell coverage of the third pharyngeal arch arteries. Although this change in phenotype could theoretically be compatible with post-natal survival, using tissue-specific inactivation of Pax9 to maintain correct palate development whilst inducing the cardiovascular defects was unable to prevent postnatal death in the mutant mice. Hyoid bone and thyroid cartilage formation were abnormal in Pax9^-/- mice.

CONCLUSIONS

Msx1 haploinsufficiency mitigates the arch artery defects in Pax9^-/- mice, potentially by maintaining the survival of the 3rd arch artery through unimpaired migration of neural crest cells to the third pharyngeal arches. With the neural crest cell derived hyoid bone and thyroid cartilage also being defective in Pax9^-/- mice, we speculate that the pharyngeal endoderm is a key signalling centre that impacts on neural crest cell behaviour highlighting the ability of cells in different tissues to act synergistically or antagonistically during embryo development.

Laryngeal Subsite Analysis of Granulomatosis With Polyangiitis (Wegener's)

Objective

To analyze specific intralaryngeal findings associated with granulomatosis with polyangiitis (GPA).

Study Design

Retrospective chart review.

Setting

Tertiary referral center.

Methods

A retrospective chart review was performed on all patients diagnosed with GPA who were evaluated at the laryngology division of Massachusetts Eye and Ear Infirmary between January 2006 and September 2019.

Results

Forty-four patients (14 male, 30 female) were evaluated for laryngeal pathology. The mean age at onset was 48 years. Nine patients (21%) were identified with only vocal fold disease, 11 (25%) with subglottic disease, and 8 (18%) with disease at the glottis and subglottis (transglottic). The remaining 16 patients (36%) had a normal airway upon examination although they presented with laryngeal symptoms. Patients with glottic disease had statistically significantly lower voice-related quality of life scores than patients with isolated subglottic stenosis.

Conclusions

Although laryngeal manifestations of GPA is often described as a subglottic disease presenting with respiratory symptoms, subsite analysis show that only 25% of patients had subglottic disease alone, with similar rates of glottic disease alone. Laryngeal subsites have different epithelial mucosa, function, and physiology, and understanding the specific sites of involvement will determine symptoms and enable better analysis of the underlying mechanisms of disease. Glottic disease is associated with a reduction in vocal fold motion and voice changes. Subglottic involvement presents more frequently with airway symptoms. Further research is necessary to better define the specific regions of laryngeal involvement in patients diagnosed with GPA.

Tissue-engineering the larynx: Effect of decellularization on human laryngeal framework and the cricoarytenoid joint

Decellularization approaches have been commonly used as alternative techniques to reconstruct tissues. However, due to the complex tissue compartmentation of the larynx, the decellularization process may not retain the characteristics necessary for the successful recreation of the larynx. The aim of this study was to assess the effect of the decellularization process on the framework of the human cadaveric larynx generally and the cricoarytenoid joint specifically. In this work, five freshly frozen human cadaveric larynges were decellularized utilizing a protocol that was previously demonstrated to be effective in decellularizing a porcine larynx. The decellularization protocol included: biological, chemical, and physical decellularization methods. Each specimen served as its own control to assess changes after decellularization. Studies and measurements included: histological, using Hematoxylin and Eosin (H&E) and Live/Dead™ stains; DNA quantification; micro-computed tomography (μ-CT) imaging; and biomechanical testing of the cricoarytenoid joints. The decellularization protocol took 12 days for each specimen. Microscopy of H&E stained samples demonstrated substantial removal of cells with preservation of the extracellular matrix that was more evident in cartilage than muscle specimens. Confocal microscope images of Live/Dead™ stained specimens also demonstrated almost complete removal of cells. Pre-decellularization cartilage-DNA quantity range was 27.0 to 336.8 ng/mg while post-decellularization DNA quantity range was 0 to 30.4 ng/mg (p = 0.031). For muscles, pre-decellularization DNA quantity range was 150.0 to 3,384.6 ng/mg, while post-decellularization DNA quantity range was 0 to 45.5 ng/mg (p = 0.031). μ-CT demonstrated preservation of the cartilaginous framework with a slight reduction of cricoarytenoid joint space. Furthermore, μ-CT demonstrated no significant reduction in the Housefield unit (p = 0.25) and mineral density (p = 0.25) after decellularization. Biomechanical testing demonstrated a non-significant reduction of forces required for anterior displacement of the arytenoid (mean reduction of forces, 0.1 ± 0.2 N, p = 0.16) and forces required for posterior displacement of the arytenoid (mean reduction of forces, 0.2 ± 0.3 N, p = 0.05). This study demonstrates effective decellularization of human larynges as evidenced by significant DNA depletion and preservation of extracellular matrix, which are outcomes that are required for a biological scaffold to regenerate a non-immunogenic larynx. The decellularization process caused minimal weakness in the cricoarytenoid joints due to treatment with multiple detergents and enzymes in the decellularization protocol.

The Importance of Inspiratory Maneuver for Benign Laryngeal Lesions

Introduction  Inspiratory maneuver corresponds to a simple method used during videolaryngoscopy to increase characterizations of laryngeal findings, through the movement of the vocal fold cover and exposure of the ligament, facilitating its evaluation.

Objective  To evaluate the increase in diagnosis of benign laryngeal lesions from the usage of inspiratory maneuvers during videolaryngoscopy in patients with or without vocal complaints.

Methods  A cross-sectional study performed from March 1 to July 1, 2018, in the Laryngology sector of a tertiary hospital. The age of the patients varied from 18 to 60 years old. They were divided into two groups, symptomatic and asymptomatic vocals, and evaluated through videolaryngoscopy together with inspiratory maneuvers. The exams were recorded and later evaluated by three trained laryngologists who determined the laryngeal lesions before and after the inspiratory maneuver.

Results  There were 60 patients in this sample, 41 of which were vocal symptomatic and 19 asymptomatic. The majority was female and the main complaint was about dysphonia. Before the inspiratory maneuver, the most observed lesions in both groups were chronic laryngitis, followed by vascular dysgenesis. After the inspiratory maneuver, sulcus vocalis was the most frequent additional finding.

Conclusion  With the inspiratory maneuver, it was possible to increase the identification of structural lesions in the vocal fold, and the most frequent lesion in patients with or without vocal complaints was sulcus vocalis.

Study of spatiotemporal liquid dynamics in a vibrating vocal fold by using a self-oscillating poroelastic model

The main purpose of this study is to investigate the spatiotemporal interstitial fluid dynamics in a vibrating vocal fold. A self-oscillating poroelastic model is proposed to study the liquid dynamics in the vibrating vocal folds by treating the vocal fold tissue as a transversally isotropic, fluid-saturated, porous material. Rich spatiotemporal liquid dynamics have been found. Specifically, in the vertical direction, the liquid is transported from the inferior side to the superior side due to the propagation of the mucosal wave. In the longitudinal direction, the liquid accumulates at the anterior-posterior midpoint. However, the contact between the two vocal folds forces the accumulated liquid out laterally in a very short time span. These findings could be helpful for exploring etiology of some laryngeal pathologies, optimizing laryngeal disease treatment, and understanding hemodynamics in the vocal folds.

3D printing for tissue engineering in otolaryngology

Airway and other head and neck disorders affect hundreds of thousands of patients each year and most require surgical intervention. Among these, congenital deformity that affects newborns is particularly serious and can be life-threatening. In these cases, reconstructive surgery is resolutive but bears significant limitations, including the donor site morbidity and limited available tissue. In this context, tissue engineering represents a promising alternative approach for the surgical treatment of otolaryngologic disorders. In particular, 3D printing coupled with advanced imaging technologies offers the unique opportunity to reproduce the complex anatomy of native ear, nose, and throat, with its import in terms of functionality as well as aesthetics and the associated patient well-being. In this review, we provide a general overview of the main ear, nose and throat disorders and focus on the most recent scientific literature on 3D printing and bioprinting for their treatment.

Imaging the Vocal Folds: A Feasibility Study on Strain Imaging and Elastography of Porcine Vocal Folds

Vocal folds are an essential part of human voice production. The biomechanical properties are a good indicator for pathological changes. In particular, as an oscillation system, changes in the biomechanical properties have an impact on the vibration behavior. Subsequently, those changes could lead to voice-related disturbances. However, no existing examination combines biomechanical properties and spatial imaging. Therefore, we propose an image registration-based approach, using ultrasound in order to gain this information synchronously. We used a quasi-static load to compress the tissue and measured the displacement by image registration. The strain distribution was directly calculated from the displacement field, whereas the elastic properties were estimated by a finite element model. In order to show the feasibility and reliability of the algorithm, we tested it on gelatin phantoms. Further, by examining ex vivo porcine vocal folds, we were able to show the practicability of the approach. We displayed the strain distribution in the tissue and the elastic properties of the vocal folds. The results were superimposed on the corresponding ultrasound images. The findings are promising and show the feasibility of the suggested approach. Possible applications are in improved diagnosis of voice disorders, by measuring the biomechanical properties of the vocal folds with ultrasound. The transducer will be placed on the vocal folds of the anesthetized patient, and the elastic properties will be measured. Further, the understanding of the vocal folds’ biomechanics and the voice forming process could benefit from it.

The Other Side of the Fascia: The Smooth Muscle Part 1

According to current scientific standards, the fascia is a connective tissue derived from two separate germ layers, the mesoderm (trunk and limbs, part of the neck) and the ectoderm (cervical tract and skull). The fascia has the property of maintaining the shape and function of its anatomical district, but it also can adapt to mechanical-metabolic stimuli. Smooth muscle and non-voluntary striated musculature originated from the mesoderm have never been properly considered as a type of fascia. They are some of the viscera present in the mediastinum, in the abdomen and in the pelvic floor. This text represents the first article in the international scientific field that discusses the inclusion of some viscera in the context of what is considered fascia, thanks to the efforts of our committee for the definition and nomenclature of the fascial tissue of the Foundation of Osteopathic Research and Clinical Endorsement (FORCE).

A Computational Study of Vocal Fold Dehydration During Phonation

While vocal fold dehydration is often considered an important factor contributing to vocal fatigue, it still remains unclear whether vocal fold vibration alone is able to induce severe dehydration that has a noticeable effect on phonation and perceived vocal effort. A three-dimensional model was developed to investigate vocal fold systemic dehydration and surface dehydration during phonation. Based on the linear poroelastic theory, the model considered water resupply from blood vessels through the lateral boundary, water movement within the vocal folds, water exchange between the vocal folds and the surface liquid layer through the epithelium, and surface fluid accumulation and discharge to the glottal airway. Parametric studies were conducted to investigate water loss within the vocal folds and from the surface after a 5-min sustained phonation under different permeability and vibration conditions. The results showed that the dehydration generally increased with increasing vibration amplitude, increasing epithelial permeability, and reduced water resupply. With adequate water resupply, a large-amplitude vibration can induce an overall systemic dehydration as high as 3%. The distribution of water loss within the vocal folds was non-uniform, and a local dehydration higher than 5% was observed even under conditions of a low overall systemic dehydration (<1%). Such high level of water loss may severely affect tissue properties, muscular functions, and phonations characteristics. In contrast, water loss of the surface liquid layer was generally an order of magnitude higher than water loss inside the vocal folds, indicating that the surface dehydration level is likely not a good indicator of the systemic dehydration.

Lateral Cricoarytenoid Release: Development of a Novel Surgical Treatment Option for Adductor Spasmodic Dysphonia in a Canine Laryngeal Model

OBJECTIVE

To investigate the efficacy of a novel adductor muscle-releasing technique designed to decrease the force of vocal fold adduction, as a potential surgical therapy for patients with adductor spasmodic dysphonia (ADSD).

STUDY DESIGN

Experimental animal study.

METHODS

A canine laryngeal model was used to assess the acute and sustained efficacy of a lateral cricoarytenoid (LCA) muscle release. A total of 34 canine hemilaryngeal preparations were divided among 7 experimental groups. The LCA muscle was separated from its cricoid cartilage origin via an open, anterior, submucosal approach. The laryngeal adductory pressures (LAP) were assessed pre- and post-muscle release via direct recurrent laryngeal nerve stimulation. Measurements were repeated at 1.5, 3, or 6 months postoperatively. Another study evaluated release of the thyroarytenoid (TA) muscle from its thyroid cartilage origin.

RESULTS

Releasing the LCA muscle demonstrated a significant decrease in LAP acutely and was maintained at all 3 time points with the aid of a barrier (P < .05). Without the barrier, the LCA muscle reattached to the cricoid. Acute release of the TA muscle did not significantly decrease the LAP.

CONCLUSIONS

The proposed LCA release procedure may provide patients with a permanent treatment option for ADSD. However, longer-term studies and human trials are needed.

Surgical anatomy of the tracheobronchial tree

Airway surgery is often indicated in the management of benign or malignant pathological processes of the tracheobronchial tree. The surgeon undertaking this type of work has, however, the responsibility of understanding the particular anatomy applicable to these structures and procedures as well as be able to correlate imaging, intraoperative findings and anatomy. These are important considerations if one wants to reduce operative morbidity and improve potential for better long-term results. This paper reviews the most important anatomic features of the tracheobronchial tree putting emphasis on those features that are important to surgeons performing surgical procedures on those organs.

Characterizing liquid redistribution in a biphasic vibrating vocal fold using finite element analysis

OBJECTIVES

Vocal fold tissue is biphasic and consists of a solid extracellular matrix skeleton swelled with interstitial fluid. Interactions between the liquid and solid impact the material properties and stress response of the tissue. The objective of this study was to model the movement of liquid during vocal fold vibration and to estimate the volume of liquid accumulation and stress experienced by the tissue near the anterior-posterior midline, where benign lesions are observed to form.

METHODS

A three-dimensional biphasic finite element model of a single vocal fold was built to solve for the liquid velocity, pore pressure, and von Mises stress during and just after vibration using the commercial finite element software COMSOL Multiphysics (Version 4.3a, 2013, Structural Mechanics and Subsurface Flow Modules). Vibration was induced by applying direct load pressures to the subglottal and intraglottal surfaces. Pressure ranges, frequency, and material parameters were chosen based on those reported in the literature. Postprocessing included liquid velocity, pore pressure, and von Mises stress calculations as well as the frequency-stress and amplitude-stress relationships.

RESULTS

Resulting time-averaged velocity vectors during vibration indicated liquid movement toward the midline of the fold, as well as upward movement in the inferior-superior direction. Pore pressure and von Misses stresses were higher in this region just after vibration. A linear relationship was found between the amplitude and pore pressure, whereas a nonlinear relationship was found between the frequency and pore pressure.

CONCLUSIONS

Although this study had certain computational simplifications, it is the first biphasic finite element model to use a realistic geometry and demonstrate the ability to characterize liquid movement due to vibration. Results indicate that there is a significant amount of liquid that accumulates at the midline; however, the role of this accumulation still requires investigation. Further investigation of these mechanical factors may lend insight into the mechanism of benign lesion formation.

A computational study of systemic hydration in vocal fold collision

Mechanical stresses develop within vocal fold (VF) soft tissues due to phonation-associated vibration and collision. These stresses in turn affect the hydration of VF tissue and thus influence voice health. In this paper, high-fidelity numerical computations are described, taking into account fully 3D geometry, realistic tissue and air properties, and high-amplitude vibration and collision. A segregated solver approach is employed, using sophisticated commercial solvers for both the VF tissue and glottal airflow domains. The tissue viscoelastic properties were derived from a biphasic formulation. Two cases were considered, whereby the tissue viscoelastic properties corresponded to two different volume fractions of the fluid phase of the VF tissue. For each case, hydrostatic stresses occurring as a result of vibration and collision were investigated. Assuming the VF tissue to be poroelastic, interstitial fluid movement within VF tissue was estimated from the hydrostatic stress gradient. Computed measures of overall VF dynamics (peak airflow velocity, magnitude of VF deformation, frequency of vibration and contact pressure) were well within the range of experimentally observed values. The VF motion leading to mechanical stresses within the VFs and their effect on the interstitial fluid flux is detailed. It is found that average deformation and vibration of VFs tend to increase the state of hydration of the VF tissue, whereas VF collision works to reduce hydration.

Decannulation and assessment of deglutition in the tracheostomized patient in non-neurocritical intensive care

With intensive care patients, decannulation and deglutition disorders are frequent reasons for otorhinolaryngological assessment. The objective of a tracheostomy is to maintain a patent airway. It does not necessarily prevent episodes of aspiration and may even favour them. When the cause that led to the tracheostomy resolves, a decannulation may be proposed. Deglutition is a complex act involving the coordinated interaction of several structures of the aerodigestive tract. Fibre-optic endoscopy and videofluoroscopy are 2 useful, complementary tools for the evaluation of patients with swallowing disorders. In managing these patients, a thorough knowledge of laryngeal and swallowing physiology, as well as of the different therapeutic alternatives, is required. Although it is not uncommon for swallowing disorders to coexist in tracheostomy patients, decannulation evaluation is not synonymous with deglutition assessment. A patient could be a candidate for decannulation and have a swallowing disorder, or a tracheostomy patient could swallow adequately. Knowing and understanding these concepts will lead to more efficient management and help to clarify communication between the intensive care physician and the otorhinolaryngologist. Ideally, a multidisciplinary team should be formed to evaluate and manage these patients.

Effects of poroelastic coefficients on normal vibration modes in vocal-fold tissues

The vocal-fold tissue is treated as a transversally isotropic fluid-saturated porous material. Effects of poroelastic coefficients on eigenfrequencies and eigenmodes of the vocal-fold vibration are investigated using the Ritz method. The study demonstrates that the often-used elastic model is only a particular case of the poroelastic model with an infinite fluid-solid mass coupling parameter. The elastic model may be considered appropriate for the vocal-fold tissue when the absolute value of the fluid-solid mass coupling parameter is larger than 10(5) kg/m(3). Otherwise, the poroelastic model may be more accurate. The degree of compressibility of the vocal tissue can also been described by the poroelastic coefficients. Finally, it is revealed that the liquid and solid components in a poroelastic model could have different modal shapes when the coupling between them is weak. The mode decoupling could cause desynchronization and irregular vibration of the folds.

Transoral laser microsurgery for laryngeal cancer: a primer and review of laser dosimetry

Transoral laser microsurgery (TLM) is an emerging technique for the management of laryngeal and other head and neck malignancies. It is increasingly being used in place of traditional open surgery because of lower morbidity and improved organ preservation. Since the surgery is performed from the inside working outward as opposed to working from the outside in, there is less damage to the supporting structures that lie external to the tumor. Coupling the laser to a micromanipulator and a microscope allows precise tissue cutting and hemostasis; thereby improving visualization and precise ablation. The basic approach and principles of performing TLM, the devices currently in use, and the associated dosimetry parameters will be discussed. The benefits of using TLM over conventional surgery, common complications and the different settings used depending on the location of the tumor will also be discussed. Although the CO₂ laser is the most versatile and the best-suited laser for TLM applications, a variety of lasers and different parameters are used in the treatment of laryngeal cancer. Improved instrumentation has lead to an increased utilization of TLM by head and neck cancer surgeons and has resulted in improved outcomes. Laser energy levels and spot size are adjusted to vary the precision of cutting and amount of hemostasis obtained.

Office-based dynamic imaging of vocal cords in awake patients with swept-source optical coherence tomography

Optical coherence tomography (OCT) is an evolving noninvasive imaging modality that has been used to image the human larynx during surgical endoscopy. The design of a long gradient index (GRIN) lens-based probe capable of capturing images of the human larynx by use of swept-source OCT during a typical office-based laryngoscopy examination is presented. In vivo OCT imaging of the human larynx is demonstrated with a rate of 40 frames per second. Dynamic vibration of the vocal folds is recorded to provide not only high-resolution cross-sectional tissue structures but also vibration parameters, such as the vibration frequency and magnitude of the vocal cords, which provides important information for clinical diagnosis and treatment, as well as fundamental research of the voice itself. Office-based OCT is a promising imaging modality to study the larynx for physicians in otolaryngology.

Liquid accumulation in vibrating vocal fold tissue: a simplified model based on a fluid-saturated porous solid theory

The human vocal fold is treated as a continuous, transversally isotropic, porous solid saturated with liquid. A set of mathematical equations, based on the theory of fluid-saturated porous solids, is developed to formulate the vibration of the vocal fold tissue. As the fluid-saturated porous tissue model degenerates to the continuous elastic tissue model when the relative movement of liquid in the porous tissue is ignored, it can be considered a more general description of vocal fold tissue than the continuous, elastic model. Using the fluid-saturated porous tissue model, the vibration of a bunch of one-dimensional fibers in the vocal fold is analytically solved based on the small-amplitude assumption. It is found that the vibration of the tissue will lead to the accumulation of excess liquid in the midmembranous vocal fold. The degree of liquid accumulation is positively proportional to the vibratory amplitude and frequency. The correspondence between the liquid distribution predicted by the porous tissue theory and the location of vocal nodules observed in clinical practice, provides theoretical evidence for the liquid accumulation hypothesis of vocal nodule formation (Jiang, Ph.D., dissertation, 1991, University of Iowa).

A fluid-saturated poroelastic model of the vocal folds with hydrated tissue

The purpose of this study is to develop a continuous model to describe the vibration of the vocal fold with hydrated tissue. This model is unique because it is based on the fluid-saturated porous solid theory. Therefore, this new model can be used to study some vocal fold characteristics that would be difficult to predict using previous models. Numerical simulations show that this model can generate self-oscillation and that its phonation threshold pressure (PTP) is 0.555 kPa. The basic outputs of this model, including fundamental frequency, maximum lateral displacement, surface dynamics, and empirical eigenfunctions, agree with previous models and experimental studies, which validates this new model. The ability to simulate the flow of liquid through the tissue is one of the important advantages of this new model. It was found that the liquid in the vocal fold tissue could be accumulated at the anterior-posterior midpoint during phonation, which could cause a pressure increase in the liquid. The liquid pressure increased from 0.033 to 0.150 kPa when the subglottal pressure increased from 0.555 kPa (PTP) to 0.7 kPa. It was believed that the liquid dynamics in the tissue during phonation could be related to the development of some vocal diseases, such as vocal nodules, edema, and so on. Therefore, we expect that this model might not only provide a more appropriate description of the vocal fold vibration, but that it could also have clinical value in investigating certain vocal fold diseases.

The glottis and subglottis: an otolaryngologist's perspective

The complexity of the glottic and subglottic region in terms of anatomy and function make this region challenging in evaluation and treatment. A thorough understanding of the complex anatomy is necessary for the management of patients who have dysphonia, vocal fold paralysis, glottic or subglottic stenosis, or complications, which may present after prolonged intubation or surgical interventions in the upper airway and the thorax.

Refinements in modeling the passive properties of laryngeal soft tissue

The nonlinear viscoelastic passive properties of three canine intrinsic laryngeal muscles, the lateral cricoarytenoid (LCA), the posterior cricoarytenoid (PCA), and the interarytenoid (IA), were fit to the parameters of a modified Kelvin model. These properties were compared with those of the thyroarytenoid (TA) and cricothyroid (CT) muscles, as well as previously unpublished viscoelastic characteristics of the human vocal ligament. Passive parameters of the modified Kelvin model were summarized for the vocal ligament, mucosa, and all five laryngeal muscles. Results suggest that the LCA, PCA, and IA muscles are functionally different from the TA and CT muscles in their load-bearing capacity. Furthermore, the LCA, PCA, and IA have a much larger stress-strain hysteresis effect than has been previously reported for the TA and CT or the vocal ligament. The variation in this effect suggests that the connective tissue within the TA and CT muscles is somehow similar to the vocal ligament but different from the LCA, PCA, or IA muscles. Further demonstrating the potential significance of grouping tissues in the laryngeal system by functional groups in the laryngeal system was the unique finding that, over their working elongation range, the LCA and PCA were nearly as exponentially stiff as the vocal ligament. This paper was written in conjunction with an online technical report (http://www.ncvs.org/ncvs/library/tech) in which comprehensive muscle data and sensitivity analysis, as well as downloadable data files and computer scripts, are made available.