Morphometry of the larynx in horizontal sections

Scale resolving simulations of the effect of glottis motion and the laryngeal jet on flow dynamics during respiration

BACKGROUND AND OBJECTIVE

The movement of the respiratory walls has a significant impact on airflow through the respiratory tract. The majority of computational fluid dynamics (CFD) studies assume a static geometry which may not provide a realistic flow field. Furthermore, many studies use Reynolds Averaged Navier-Stokes (RANS) turbulence models that do not resolve turbulence structure. Combining the application of advanced scale-resolving turbulence models with moving respiratory walls using CFD will provide detailed insights into respiratory flow structures.

METHODS

This study simulated a complete breathing cycle involving inhalation and exhalation in a nasal cavity to trachea geometry that incorporated moving glottis walls. A second breathing cycle was simulated with static glottis walls for comparison. A recently developed hybrid RANS-LES turbulence model, the Stress-Blended Eddy Simulation (SBES), was incorporated to resolve turbulent flow structures in fine detail for both transient simulations. Transient results were compared with steady-state RANS simulations for the same respiratory geometry.

RESULTS

Glottis motion caused substantial effects on flow structure through the complete breathing cycle. Significant flow structure and velocity variations were observed due to glottal motion, primarily in the larynx and trachea. Resolved turbulence structures using SBES showed an intense mixing section in the glottis region during inhalation and in the nasopharynx during expiration, which was not present in the RANS simulations.

CONCLUSION

Transient simulations of a realistic breathing cycle uncovered flow structures absent in simulations with a constant flow rate. Furthermore, the incorporation of glottis motion impacted airflow characteristics that suggest rigid respiratory walls do not accurately describe respiratory flow. Future research in respiratory airflow should be conducted using transient scale-resolving models in conjunction with moving respiratory walls to capture flow structures in detail.

Novel and pragmatic exploration of variation in glottic parameters in non-parallel versus parallel vocal cord CT planes with potential reporting pitfalls

Oblique orientation of vocal cord demands strict compliance, by technicians and clinicians, to the recommended parallel plane CT scan of larynx. Repercussions of non-compliance has never been investigated before. We aimed to observe influence of non-parallel vocal cord plane CT scan on qualitative and quantitative glottic parameters, keeping parallel plane CT as a standard for comparison. Simultaneous identification of potential suboptimal imaging sequelae as a result of unformatted CT plane was also identified. In this study we included 95 normal adult glottides and retrospectively analyzed their anatomy in two axial planes, non-parallel plane ① and parallel to vocal cord plane ②. Qualitative (shape, structures at glottic level) and quantitative (anterior commissure ACom, vocal cord width VCw, anteroposterior AP, transverse Tr, cross-sectional area CSA) glottic variables were recorded. Multivariate statistical analysis was used to predict pattern and their impact on glottic anatomy. Plane ① displayed supraglottic features in glottis; adipose (90.5%) and split thyroid laminae (70.6%). Other categorical variables: atypical shape, submental structures and multilevel vertebral crossing were also in majority. All glottic dimensions varied significantly between two planes with most in ACom (-5.8mm) and CSA (-15.0 mm2). In contrast, plane ② manifested higher VCw (>73%), Tr (66.3%), CSA (64.2%) and AP (44.2%) measurements. On correlation analysis, variation in ACom, CSA, Tr was positively associated with VC or plane obliquity (p<0.05). This variability was more in obese and short necked subjects. Change in one parameter also modified other significantly i.e., ACom versus AP and CSA versus Tr. Results indicated statistically significant change in subjective and objective anatomical parameters of glottis on non-application of appropriate CT larynx protocol for image analysis hence highlighting importance of image reformation.

Comparison of standard weight-based and thenar eminence dimension-based selection of I-gel in pediatric patients - A randomized controlled study

Background and Aim

Supraglottic airway devices are increasingly being used for airway management. I-gel is being widely used even for pediatric patients. Although the weight-based selection of the size of the device seems to be the standard technique, this method may not be possible in all patients. The aim of the study was to compare the standard weight-based method with the thenar eminence dimension-based method for I-gel selection.

Material and Methods

A prospective randomized study was conducted on 74 pediatric patients of either sex, aged between 6 months and 15 years, belonging to American Society of Anesthesiologists (ASA) physical status I, II, and III and who were posted for various surgical procedures under general anesthesia. The study population was divided into two groups of 37 patients each. I-gel was inserted based on weight in group A patients and based on thenar eminence size in group B patients. Parameters like first attempt success rate, ease of insertion, and complications were compared between the two groups using Student's t-test and Chi-square test.

Results

The demographic values between the groups were comparable. The first attempt success rate was 97.4% in group A and 91.7% in group B (P = 0.358). Insertion of I-gel was unsuccessful in two patients in group B. Two patients of group B had blood staining of the device. None of the patients had complications related to insertion.

Conclusion

The thenar eminence dimension can be used instead of weight while choosing the size of I-gel in pediatric patients. None of the patients had complications related to device insertion.

Laryngeal Framework Surgical Anatomy: A Radiological Study

PURPOSE

Awareness of variations in laryngeal anatomy among different age and gender groups is crucial during laryngeal framework surgery. The aim of this study is to demonstrate the relationship between gender and laryngeal radiologic morphometrics among different age groups and the applicability of important anatomical landmarks of laryngeal surgery.

METHODS

Laryngeal images of 180 adult patients older than 18 years of age were obtained by computed tomography and assessed. A total of 11 measurements of important laryngeal landmarks were taken from the patients' computed tomography images. Results were subgrouped according to gender and age, and these groups were compared for each measurement.

RESULTS

The majority of laryngeal measurements obtained in the study were higher in males than females, with the exception of the interlaminar angle. The mean interlaminar angle value was 88.27°± 14.99 for males and 103.04°± 14.81 for females (P <0.005). The distance from the anterior commissure to the inferior border of the thyroid cartilage was 10.46 ± 2.5 mm for males and 7.72 ± 1.9 mm for females. The anterior commissure locates slightly higher than the midpoint of the distance from the thyroid notch to the thyroid inferior border. The shortest distance between the muscular process of the arytenoid cartilage and the thyroid cartilage was found to be 9.60 ± 3.47 mm for males and 7.72 ± 2.33 mm for females (P <0.001).

CONCLUSION

Observation of obvious diversities in the size and distance of the important laryngeal structures between the gender groups is an important factor to be considered for successful laryngeal framework surgery. Also, using the midpoint of the thyroid cartilage as a landmark for anterior commissure is a practical method during surgery, especially for thyroplasty.

Normative data for certain vocal fold biomarkers among young normophonic adults using ultrasonography

PURPOSE

The current study aimed to profile vocal fold morphology, vocal fold symmetry, gender and task-specific data for vocal fold length (VFL) and vocal fold displacement velocity (VFDV) in young normophonic adults in the age range of 18-30 years using ultrasonography (USG).

METHODS

Participants underwent USG across quiet breathing, /a/ phonation and /i/ phonation tasks, and acoustic analysis was conducted to explore the relationship between USG and acoustic measures.

RESULTS

The study found that males have longer vocal folds than females, and overall greater velocities were observed in /a/ phonation, followed by /i/ phonation, with the lowest velocity observed in the quiet breathing task.

CONCLUSIONS

The obtained norms can be used as a quantitative benchmark for analyzing the vocal fold behavior in young adults.

Chondrolaryngoplasty

Chondrolaryngoplasty is a surgical procedure that reduces the prominence of the thyroid notch. Although frequently performed on transgender (man to woman) women, anyone wishing to reduce the prominence of their thyroid notch for aesthetic purposes may consider undergoing a chondrolaryngoplasty. Direct visualization of the vocal cords with flexible laryngoscopy and intraoperative needle localization of the anterior commissure directs the extent of resection, helps increase safety, and avoids devastating postoperative voice complications. This procedure can be safely performed in combination with other facial feminization surgeries.

Post-pubertal developmental trajectories of laryngeal shape and size in humans

Laryngeal morphotypes have been hypothesized related to both phonation and to laryngeal pathologies. Morphotypes have not been validated or demonstrated quantitatively and sources of shape and size variation are incompletely understood but are critical for the explanation of behavioral changes (e.g., changes of physical properties of a voice) and for therapeutic approaches to the larynx. This is the first study to take this crucial step and results are likely to have implications for surgeons and speech language pathologists. A stratified human sample was interrogated for phenotypic variation of the vocal organ. First, computed tomography image stacks were used to generate three-dimensional reconstructions of the thyroid cartilage. Then cartilage shapes were quantified using multivariate statistical analysis of high dimensional shape data from margins and surfaces of the thyroid cartilage. The effects of sex, age, body mass index (BMI) and body height on size and shape differences were analyzed. We found that sex, age, BMI and the age-sex interaction showed significant effects on the mixed sex sample. Among males, only age showed a strong effect. The thyroid cartilage increased in overall size, and the angulation between left and right lamina decreased in older males. Age, BMI and the age-height interaction were statistically significant factors within females. The angulation between left and right lamina increased in older females and was smaller in females with greater BMI. A cluster analysis confirmed the strong age effect on larynx shape in males and a complex interaction between the age, BMI and height variables in the female sample. The investigation demonstrated that age and BMI, two risk factors in a range of clinical conditions, are associated with shape and size variation of the human larynx. The effects influence shape differently in female and male larynges. The male-female shape dichotomy is partly size-dependent but predominantly size-independent.

Analysis of the Effectiveness of Arytenoidectomy and Posterior Cordectomy with the Use of CFD Airflow Measurements in Patients with BVFP: A Retrospective Study

PURPOSE

Bilateral vocal fold paralysis (BVFP) is a rare larynx disease manifested by dyspnea, which often requires surgical treatment. The aim of the study is to determine the effectiveness of unilateral arytenoidectomy with posterior cordectomy in the treatment of BVFP using the computational fluid dynamics (CFD) method.

METHODS

This study included 33 patients with BVFP who underwent unilateral laser arytenoidectomy with posterior cordectomy. Glottis area measurements and spirometry, as well as a self-assessment of respiratory efficiency were performed before the surgery and after the recovery period. Using the CFD method, computer models of the glottis were made. Then, changes in air pressure gradient and maximum air velocity at the level of glottis were calculated, and local fields of pressure and air velocities were obtained.

RESULTS

The values of glottal surface area (S), spirometry parameters (forced expiratory volume in one second (FEV1), forced vital capacity (FVC), and peak expiratory flow (PEF)), inlet air velocity at the glottal level as well as patients self-assessment of respiratory efficiency turned out to be significantly higher after the operation. The values of maximum velocity at the glottal level, pressure gradient at the glottal level turned out to be significantly lower after the surgery. We observed that the greater the increase in glottal surface area, the greater the decrease in self-assessment scales (visual analogue scale (VAS) and Medical Research Council (MRC)). Increased levels of spirometry parameters after the surgery correlated with smaller decrease of PEF-dependent pressure gradient at the glottal level (PEFΔP CFD).

CONCLUSION

Unilateral laser arytenoidectomy with posterior cordectomy is an effective method for the treatment of BVFP. CFD is a useful tool to determine and visualize the effectiveness of surgical treatment in BVFP.

Ultrasonography measurement of glottic transverse diameter and subglottic diameter to predict endotracheal tube size in children: a prospective cohort study

We aimed to determine the correlation between mid-glottic transverse diameter/subglottic diameter and outer diameter of endotracheal tube (ETT) by ultrasonography in children. Ninety-five patients aged 1–8 years who underwent general anesthesia were included. Ultrasonography of glottic/subglottic transverse diameter was performed by two investigators after patients were anesthetized and when the train of four showed ≤ 4. The subglottic diameter was measured at the mid cricoid cartilage. The mid-glottic transverse diameter was measured at the mid-point of true vocal fold triangle whereas the distance between arytenoids was considered as the glottic transverse diameter. Linear regression models and correlation coefficients (r) were used to determine the best formula of glottic/subglottic transverse diameter to predict the outer diameter of ETT. The predicted outer diameter of ETT formula for subglottic diameter, mid-glottic transverse diameter, and glottic transverse diameter were 5.7 + (subglottic_mm/3) with an r of 0.45, 5.5 + (midglottic_mm/2) with an r of 0.47, and 5.7 + (glottic_mm/4) with an r of 0.46, respectively. The correlation between subglottic diameter and mid-glottic transverse diameter was 0.50. Subglottic/mid-glottic/glottic transverse diameter formulae had moderate correlations with the outer diameter of ETT. The glottic/mid-glottic transverse diameter can be used alternatively to predict the ETT size.

Trial registration: Thai Clinical Trial Registry: TCTR20191022002 Registered 22/10/2019—Prospectively registered, https://www.thaiclinicaltrials.org/# TCTR20191022002.

Recommended Maximum Laryngeal Prominence Size in Adult Females: A Cross-Sectional Study Proposing a Laryngeal Prominence Size Standard for Chondrolaryngoplasty in Male-to-Female Transgender Individuals

BACKGROUND

Although the World Professional Association for Transgender Health has provided international, multidisciplinary, evidence-based standards of care for various aspects of transgender health care, there is a lack of evidence-based guidelines for facial feminization surgery, including chondro laryngoplasty. The aim of this study was to define the recommended maximum laryngeal prominence size in adult females to propose an evidence-based laryngeal prominence size standard for chondrolaryngoplasty in male-to-female transgender individuals.

METHODS

This cross-sectional study was conducted in a tertiary care hospital. The study sample consisted of cisgender patients aged 18 to 60 years old with no history of surgery or radiotherapy in the head and neck area who visited the Otolaryngology/Head and Neck Surgery outpatient clinic. Laryngeal prominence size data were collected using three-dimensional scanning of the head and neck area.

RESULTS

Seventy-nine participants, 43 males and 36 females, were included in data analysis. Laryngeal prominence size was larger in male participants (median, 0.16 mm; range, 0 to 9.40 mm) than in female participants (median, 0.00 mm; range, 0 to 1.24 mm) (p < 0.001). The proportion of participants with a laryngeal prominence size larger than 0 mm was greater in male participants (55.81 percent) than in female participants (22.22 percent) (p = 0.002).

CONCLUSIONS

To the authors' knowledge, this is the first study to assess laryngeal prominence size in the general population. Their results suggest that 2 mm would be the recommended maximum laryngeal prominence size in females. Therefore, a laryngeal prominence size standard of 2 mm could be considered for chondrolaryngoplasty in male-to-female transgender individuals.

A proposal for needle projections in transcutaneous injection laryngoplasty using three-dimensionally reconstructed CT scans

PURPOSE

This study aims to determine laryngeal dimension in relation to all three transcutaneous injection laryngoplasty (TIL) approaches (thyrohyoid, transthyroid and cricothyroid) using three-dimensionally reconstructed Computed Tomography (CT) scan and compare the measurements between sex, age group and ethnicity.

METHODS

CT scans of the neck of two hundred patients were analysed by two groups of raters. For thyrohyoid approach, mean distance from the superior border of the thyroid cartilage to the laryngeal cavity (THd) and mean angle from the superior border of the thyroid cartilage to mid-true cords (THa) were measured. For transthyroid approach, mean distance from mid-thyroid cartilage to mid-true cords (TTd) and Hounsfield unit (HU) at mid-thyroid cartilage (TTc) were measured. For cricothyroid approach, mean distance from the inferior border of the thyroid cartilage to the laryngeal cavity (CTd) and mean angle from the inferior border of the thyroid cartilage to mid-true cords (CTa) were measured.

RESULTS

There were statistically significant differences between males and females for all measurements except for CTa (p < 0.0001). No significant difference across age groups and ethnicities were found for all three approaches (p > 0.05). There was a significant fair positive correlation between age and TTc (p = 0.0002). For all measurements obtained, there were moderate to excellent inter-group consistency and intra-rater reliability.

CONCLUSION

This study demonstrated a significant sex dimorphism that may influence the three TIL approaches except for needle angulation in the cricothyroid approach. The knowledge of laryngeal dimension is important to increase success in TIL procedure.

Age-related Change of the Dimensions of the Cricoid Cartilage in Adults

OBJECTIVES

To measure the dimensions of the cricoid cartilage in adults and to investigate the age-related change of the dimensions of the cricoid cartilage.

METHODS

After performing the multiplanar reconstruction and correcting the slant of the cervical computed tomography scans, the transverse and anteroposterior internal diameters of the inlet (TD-in and APD-in) and outlet (TD-out and APD-out) of the cricoid cartilage were measured, respectively. The angle between the arch and lamina of the cricoid cartilage in the middle sagittal plane was measured. The ratios of transverse to anteroposterior diameter for the inlet (Ratio-in) and outlet (Ratio-out) of the cricoid cartilage were calculated, respectively.

RESULTS

A total of 1200 adults were included in this study, with 600 males and 600 females. The TD-in is the smallest cricoid diameter and the APD-in is the largest cricoid diameter. The mean cricoid diameters and the cricoid angle in males were larger than those in females. The cricoid inlet is oval shaped and the cricoid cartilage is "funnel-shaped" in the middle sagittal plane. The shape of the outlet of the cricoid cartilage varies greatly among individuals. In males, the APD-in and APD-out were negatively correlated with age while the Ratio-in and Ratio-out was positively correlated with age. In females, the APD-out were negatively correlated with age while the Ratio-out was negatively correlated with age.

CONCLUSIONS

The dimensions of the cricoid cartilage change as age advances in adult population and the sexual dimorphism of the cricoid outlet occurs after 50 years old.

Tracheal tube size in adults undergoing elective surgery - a narrative review

Tracheal tubes are routinely used in adults undergoing elective surgery. The size of the tracheal tube, defined by its internal diameter, is often generically selected according to sex, with 7-7.5 mm and 8-8.5 mm tubes recommended in women and men, respectively. Tracheal diameter in adults is highly variable, being narrowest at the subglottis, and is affected by height and sex. The outer diameter of routinely used tracheal tubes may exceed these dimensions, traumatise the airway and increase the risk of postoperative sore throat and hoarseness. These complications disproportionately affect women and may be mitigated by using smaller tracheal tubes (6-6.5 mm). Patient safety concerns about using small tracheal tubes are based on critical care populations undergoing prolonged periods of tracheal intubation and not patients undergoing elective surgery. The internal diameter of the tube corresponds to its clinical utility. Tracheal tubes as small as 6.0 mm will accommodate routinely used intubation aids, suction devices and slim-line fibreoptic bronchoscopes. Positive pressure ventilation may be performed without increasing the risk of ventilator-induced lung injury or air trapping, even when high minute volumes are required. There is also no demonstrable increased risk of aspiration or cuff pressure damage when using smaller tracheal tubes. Small tracheal tubes may not be safe in all patients, such as those with high secretion loads and airflow limitation. A balanced view of risks and benefits should be taken appropriate to the clinical context, to select the smallest tracheal tube that permits safe peri-operative management.

A three-dimensional vocal fold posturing model based on muscle mechanics and magnetic resonance imaging of a canine larynx

In this work, a high-fidelity three-dimensional continuum model of the canine laryngeal framework was developed for simulating laryngeal posturing. By building each muscle and cartilage from magnetic resonance imaging (MRI), the model is highly realistic in anatomy. The muscle mechanics is modeled using the finite-element method. The model was tested by simulating vocal fold postures under systematic activations of individual as well as groups of laryngeal muscles, and it accurately predicted vocal fold posturing parameters reported from in vivo canine larynges. As a demonstration of its application, the model was then used to investigate muscle controls of arytenoid movements, medial surface morphology, and vocal fold abduction. The results show that the traditionally categorized adductor and abductor muscles can have opposite effects on vocal fold posturing, making highly complex laryngeal adjustments in speech and singing possible. These results demonstrate that a realistic comprehensive larynx model is feasible, which is a critical step toward a causal physics-based model of voice production.

Biomechanical study of the thyroid cartilage: A model of bi-digital strangulation

The presence of fracture on neck elements is an indication of violence. Both the hyoid bone and the larynx can be damaged by a strangulation mechanism. Thyroid cartilage, more specifically, may present lesions in response to this mechanical stress. These lesions result in fractures at the bases of the horns of the thyroid cartilage. This study focuses on the thyroid cartilage behavior in cases of bi-digital strangulation, using an anthropometric and biomechanical approach. To develop a biomechanical model, we performed an anthropometric study taking into account 14 distances measurements as well as 3 measurements of angles. These measures allowed us to determine a significant sexual dimorphism between individuals. Then, we define 6 morphologies models, composed of 3 females and 3 males individuals. In order to visualize the ossification of the cartilage, each model has been tested with bone properties. Strangulation cases were simulated by applying an imposed velocity of 0.4m/s then 1m/s. We observed different behaviors of the thyroid cartilage according to the sex and the morphology.

Computed Tomography Data to Generate a Reproducible, Anatomically Accurate Hemilaryngeal Model

Objective

The study aims to demonstrate the reproducibility and feasibility of creating a hemilaryngeal model with a medialized vocal fold (VF) using 3-dimensional (3D) modeling techniques in both healthy larynges and those affected by cancer.

Study Design

Three-dimensional modeling of human larynges.

Setting

Tertiary academic referral center and regenerative medicine laboratory.

Subjects and Methods

Computed tomography (CT) scans from 10 healthy control and 10 patients with laryngeal cancer were segmented and imported into 3D modeling software. The larynx was cut sagittally to create a hemilaryngeal model and the vocal fold medialized. Measurements were taken from the CT and 3D model data and compared.

Results

All control modeling data closely matched the CT data and were not statistically different from each other. There was a significant correlation between subglottic anteroposterior diameter and VF length ( r2 = 0.78, P = .0008), and it may be a valuable tool to infer true VF dimension in cases where disruption has occurred. The modeling data from patients with cancer did not show statistical difference to the control data, showing that accurate modeling can also be achieved in patients with laryngeal cancer.

Conclusion

CT scan-based 3D modeling of the larynx and VF is possible and reproducible. The results closely match those previously reported in the literature and can also be replicated in cases with laryngeal cancer. This study paves the way for future de novo fabricated laryngeal scaffolds that can be synthesized using 3D printers and tailored to meet surgical demands.

Observational study of laryngoscopy plus flow-volume loops during exercise

Laryngoscopy is the gold standard to diagnose exercise‐induced laryngeal obstruction, though inspiratory flow‐volume loop may provide a clue. We combined tidal flow‐volume loop analysis plus laryngoscopy during exercise and found that cigar‐shaped – not flattened – inspiratory loops are associated with obstruction. Pursed‐lip breathing slows inhalation thereby reducing vocal fold adduction.

Phonation Analysis Combined with 3D Reconstruction of the Thyroarytenoid Muscle in Aged Ovine Ex Vivo Larynx Models

OBJECTIVE

The aim of the study was to establish a basic data set of combined functional and anatomical measures of aged sheep larynges using ex vivo models. Combining these two approaches in one and the same larynx is an unmet goal so far yet is important as newer treatment strategies aim to preserve the organ structure and new assessment tools are required. Ovine larynges were used as their dimensions, and muscle fiber type distribution highly resemble the human larynx.

STUDY DESIGN

Ex vivo animal study.

METHODS

Larynges of six sheep (~9 years of age) were subjected to ex vivo functional phonatory experiments. Phonatory characteristics were analyzed as a function of longitudinal vocal fold (VF) prestress. Anatomical measurements of the same larynges comprised micro-computed tomography scans followed by three-dimensional (3D) reconstructions. Using specially adapted radiological scan protocols with subsequent 3D reconstruction, muscle volumes, surface areas, and anatomical measurements were computed.

RESULTS

Increasing longitudinal prestress yielded higher subglottal pressure (P_S) for the same airflow. Quantitative differences to previous studies-such as the increased P_S and increased phonation threshold pressure-were detected. We achieved excellent visualization of the laryngeal muscles and framework, resulting in accurate 3D reconstructions for quantitative analysis. We found no significant intraindividual volume differences of the thyroarytenoid muscles.

CONCLUSION

The established protocol allows precise functional and anatomical measures. The data created provide a reference data set for upcoming therapeutic strategies (eg, growth factor therapy, functional electrical stimulation) that target essential structures of the VFs such as the laryngeal muscles and/or the VF mucosa.

Cilia-mediated Hedgehog signaling controls form and function in the mammalian larynx

Acoustic communication is fundamental to social interactions among animals, including humans. In fact, deficits in voice impair the quality of life for a large and diverse population of patients. Understanding the molecular genetic mechanisms of development and function in the vocal apparatus is thus an important challenge with relevance both to the basic biology of animal communication and to biomedicine. However, surprisingly little is known about the developmental biology of the mammalian larynx. Here, we used genetic fate mapping to chart the embryological origins of the tissues in the mouse larynx, and we describe the developmental etiology of laryngeal defects in mice with disruptions in cilia-mediated Hedgehog signaling. In addition, we show that mild laryngeal defects correlate with changes in the acoustic structure of vocalizations. Together, these data provide key new insights into the molecular genetics of form and function in the mammalian vocal apparatus.

DOI:http://dx.doi.org/10.7554/eLife.19153.001

Nearly all animals communicate using sound. In many cases these sounds are in the form of a voice, which in mammals is generated by a specialized organ in the throat called the larynx. Millions of people throughout the world have voice defects that make it difficult for them to communicate. Such defects are distinct from speech defects such as stuttering, and instead result from an inability to control the pitch or volume of the voice. This has a huge impact because our voice is so central to our quality of life.

A wide range of human birth defects that are caused by genetic mutations are known to result in voice problems. These include disorders in which the Hedgehog signaling pathway, which allows cells to exchange information, is defective. Projections called cilia that are found on the outside of many cells transmit Hedgehog signals, and birth defects that affect the cilia (called ciliopathies) also often result in voice problems.

Although the shape of the larynx has a crucial effect on voice, relatively little is known about how it develops in embryos. Mice are often studied to investigate how human embryos develop. By studying mouse embryos that had genetic mutations similar to those seen in humans with ciliopathies, Tabler, Rigney et al. now show that many different tissues interact in complex ways to form the larynx. A specific group of cells known as the neural crest was particularly important. The neural crest helps to form the face and skull and an excess of these cells causes face and skull defects in individuals with ciliopathies. Tabler, Rigney et al. show that having too many neural crest cells can also contribute towards defects in the larynx of mice with ciliopathies, despite the larynx being in the neck.

Further investigation showed that the Hedgehog signaling pathway was required for the larynx to develop properly. Furthermore, recordings of the vocalizations of the mutant mice showed that they had defective voices, thus linking the defects in the shape of the larynx with changes in the vocalizations that the mice made.

Overall, Tabler, Rigney et al. show that mice can be used to investigate how the genes that control the shape of the larynx affect the voice. The next step will be to use mice to investigate other genetic defects that cause voice defects in humans. Further research in other animals could also help us to understand how the larynx has evolved.

DOI:http://dx.doi.org/10.7554/eLife.19153.002

A Novel, Adaptable Laryngeal Mask to Facilitate a Percutaneous Dilatational Tracheostomy: Proof-of-Concept Prototype Demonstration on a Mannequin Model and Cadaver

BACKGROUND

Most percutaneous dilatational tracheostomy (PDT) mortalities result from airway-related complications. Improved airway pressure management and gas delivery are targets for innovation. This study describes an adaptable laryngeal mask (ALM) designed to remove the bronchoscope from the endotracheal tube (ETT) and place it in a separate lumen. Airflow and device efficacy were evaluated during PDTs with an ALM on mannequins and cadavers, respectively.

METHODS

Procedures were completed by a single physician using an 8.0 mm ETT and the Ciaglia Blue Rhino method on simulation mannequins (TruCorp AirSim Traci) and fresh-frozen cadavers. Mannequin simulation tested the respiratory capabilities of an ALM utilizing a BioPac spirometer and a Maquet Servo ventilator. Qualitative analysis on device efficacy was performed on 2 fresh-frozen cadavers (1 male, 1 female).

RESULTS

Preliminary ventilation testing on a PDT-able mannequin using the ALM showed an increase in airflow reaching the lungs compared with a deflated ETT. During mannequin and cadaver testing, the ALM was placed over the in situ ETT effectively, thereby removing the bronchoscope from the ETT while maintaining a continuous visual of the incision site. Both mannequin and cadaveric testing using an ALM enabled a single physician to safely perform the PDT procedure with minimal assistance.

CONCLUSIONS

Initial testing using an ALM during PDT on mannequins and cadavers showed an improvement in airflow and the removal of the bronchoscope from the ETT, respectively. Further studies using the ALM in a patient population compared with standard techniques would be useful.

Novel Anatomic Characteristics of the Laryngeal Framework

Objective

The thyroid cartilage (TC) in men has a more prominent thyroid notch and a narrower interlaminae angle (ILA) as compared with women. Anatomy textbooks classically stipulate that the ILA is 90° in men and 120° in women. Our observation, based on thyroid chondroplasty operations, of a much narrower angle led to the current investigation.

Study Design

Cohort imaging study.

Setting

Tertiary academic referral center.

Subjects and Methods

Computed tomography angiography neck images of adult patients were studied. The ILA was measured on 2 axial planes: at the level of the vocal processes (and the upper portion of thyroarytenoid muscles) and 5 mm superior and parallel to the former. The anterior projection of the TC and the vertical dimensions of the midline cricothyroid membrane (CTM) were also measured.

Results

A total of 126 patients were included in the study. The average ILAs were 63.5°±20.6° and 93.3°±16.6° for men and women, respectively ( P < 10−14), and were significantly narrower at the upper level in comparison with the vocal process level ( P < 10−7 for men, P = .004 for women). The anterior projection of the TC in men was more prominent as compared with women ( P = .0003) and significantly correlated with the ILA ( P = .0159). The length of the midline CTM was 11.1±2.3 mm in men and 10.3±1.7 mm in women ( P = .0355).

Conclusions

The ILA is narrower than that reported in the classic anatomy textbooks. In male patients, the upper part of the TC becomes narrower and projects anteriorly like a “jug’s spout.” The mean vertical dimension of the midline CTM was 10 to 11 mm.

An Evaluation of Thyromental Distance-based Method or Weight-based Method in Determining the Size of the Laryngeal Mask Airway Supreme: A Randomized Controlled Study

The successful placement of Laryngeal Mask Airway (LMA) Supreme in adults largely depends on right selection of its size. Most anesthesiologists determine the size of LMA according to patients' body weight, which does not always work well. An alternative method should be established to guarantee higher efficacy of ventilation through LMA Supreme placement. This controlled study was designed to compare the efficacy of LMA Supreme placement, when the size of it is determined by body weight or by thyromental distance. Eighty healthy individuals with American Society of Anesthesiologists physical status 1 to 2 scheduled for elective ambulatory surgery were randomly allocated into 2 groups: thyromental distance-based group (n = 40) and weight-based group (n = 40). Efficacy of controlled ventilation through LMA, easy of device placement, and pharyngeal sealing were evaluated between the groups. The tidal volume under 10 cm H2O pressure-controlled ventilation in thyromental distance-based group was significantly higher than that in weight-based group (523.9 ± 135.4 vs 477.1 ± 185.6; P = 0.031). The number of patients who achieved "excellent" tidal volume (>8 mL/kg) were significantly more in the thyromental distance-based group (24/40 vs 13/40; P = 0.019). Among overweight patients (body mass index >23), those who achieved "excellent" tidal volume (>8 mL/kg) under 10 cm H2O pressure-controlled ventilation were also more in thyromental distanced-based group than in weight-based group (11/24 vs 2/24; P = 0.031). The time taken for successful insertion was shorter with the thyromental distance-based group compared with the weight-based group (54.6 ± 33.6 vs 87.8 ± 98.9; P = 0.021). Oropharyngeal leak pressure was pretty close between the 2 groups (26.4 ± 5.1 vs 25.0 ± 5.7 cm H2O; P = 0.180). In terms of guaranteeing better positive pressure ventilation, facilitating device placement, and reliable pharyngeal sealing, thyromental distance-based method can be a better option compared with the weight-based method for LMA Supreme size selection.

Quantification of Porcine Vocal Fold Geometry

OBJECTIVE

The aim of this study was to quantify porcine vocal fold medial surface geometry and three-dimensional geometric distortion induced by freezing the larynx, especially in the region of the vocal folds.

STUDY DESIGN

The medial surface geometries of five excised porcine larynges were quantified and reported.

METHODS

Five porcine larynges were imaged in a micro-CT scanner, frozen, and rescanned. Segmentations and three-dimensional reconstructions were used to quantify and characterize geometric features. Comparisons were made with geometry data previously obtained using canine and human vocal folds as well as geometries of selected synthetic vocal fold models.

RESULTS

Freezing induced an overall expansion of approximately 5% in the transverse plane and comparable levels of nonuniform distortion in sagittal and coronal planes. The medial surface of the porcine vocal folds was found to compare reasonably well with other geometries, although the compared geometries exhibited a notable discrepancy with one set of published human female vocal fold geometry.

CONCLUSIONS

Porcine vocal folds are qualitatively geometrically similar to data available for canine and human vocal folds, as well as commonly used models. Freezing of tissue in the larynx causes distortion of around 5%. The data can provide direction in estimating uncertainty due to bulk distortion of tissue caused by freezing, as well as quantitative geometric data that can be directly used in developing vocal fold models.

Realistic glottal motion and airflow rate during human breathing

The glottal geometry is a key factor in the aerosol delivery efficiency for treatment of lung diseases. However, while glottal vibrations were extensively studied during human phonation, the realistic glottal motion during breathing is poorly understood. Therefore, most current studies assume an idealized steady glottis in the context of respiratory dynamics, and thus neglect the flow unsteadiness related to this motion. This is particularly important to assess the aerosol transport mechanisms in upper airways. This article presents a clinical study conducted on 20 volunteers, to examine the realistic glottal motion during several breathing tasks. Nasofibroscopy was used to investigate the glottal geometrical variations simultaneously with accurate airflow rate measurements. In total, 144 breathing sequences of 30s were recorded. Regarding the whole database, two cases of glottal time-variations were found: "static" or "dynamic" ones. Typically, the peak value of glottal area during slow breathing narrowed from 217 ± 54 mm(2) (mean ± STD) during inspiration, to 178 ± 35 mm(2) during expiration. Considering flow unsteadiness, it is shown that the harmonic approximation of the airflow rate underevaluates the inertial effects as compared to realistic patterns, especially at the onset of the breathing cycle. These measurements provide input data to conduct realistic numerical simulations of laryngeal airflow and particle deposition.

Evaluation of True Vocal Fold Growth as a Function of Age

Objective

To evaluate change in true vocal fold length as a function of age.

Study Design

Prospective study.

Setting

Tertiary aerodigestive center.

Subjects and Methods

In total, 205 patients (aged 1 month to 20 years), of whom 87 (42.4%) were female and 118 (57.6%) male, were included. Lengths of the total vocal fold (TVFL), membranous vocal fold (MVFL), and cartilaginous vocal fold (CVFL) were measured during direct laryngoscopy. Membranous-to-cartilaginous (M/C) ratios were calculated.

Results

For patients younger than 1 year, mean (SD) MVFL was 4.4 (1.3) mm for females and 4.9 (1.8) mm for males. At age 17 years, mean (SD) MVFL was 12.3 (2.1) mm for females and 14.0 (1.4) mm for males. Mean TVFL, MVFL, and CVFL increased an average of 0.7 mm, 0.5 mm, and 0.2 mm per year in linear fashion, respectively (linear regression, P < .0001). The M/C ratio did not significantly change with age ( P = .33). Mean TVFL, MVFL, and CVFL showed no statistical difference between males and females ( P = .27, .11, and .75, respectively).

Conclusion

This is the largest longitudinal pediatric study specifically examining vocal fold length as a function of age. Each length of the true vocal fold appeared to linearly increase for both females and males. The M/C ratio remained relatively constant, unlike previously reported data, possibly due to in vivo vs cadaveric measurements. These findings suggest that critical periods of development in females and males are not explainable by changes in vocal fold length alone, and other factors such as vocal fold layers need further exploration.

Glottic and skull indices in canine brachycephalic airway obstructive syndrome

BACKGROUND

Forty dogs presented for brachycephalic airway obstructive syndrome with laryngeal collapse not over 1st degree (saccule eversion) underwent glottis endoscopic and radiographic skull measurements before surgery. Fifteen Pugs, fifteen French and ten English Bulldogs were included. The goals were prospectively to compare three common brachycephalic breeds for anatomical differences regarding glottis and skull measurements, and to assess if any correlation between glottis and skull measurements was present. Linear measurements were used to obtain glottis and skull indices. Correlations between glottis and skull indices and glottic measurements were evaluated. Finally, glottis indices were compared among the three breeds.

RESULTS

No correlation was found for glottis and skull indices. The glottic index differed among the three breeds (smaller in Pugs and higher in English Bulldogs), ultimately representing a morphologic indicator of the different larynx shape in the three breeds (more rounded in English Bulldogs, more elliptical in Pugs and in-between in French Bulldogs).

CONCLUSIONS

The lack of correlation between skull/glottic indices does not support skull morphology as predictor of glottic morphology. As Pugs had the lowest glottic index, it may be speculated that Pugs' original narrow glottic width may predispose to further progressive respiratory deterioration more easily than in the other two breeds.

Three-dimensional reconstruction of human vocal folds and standard laryngeal cartilages using computed tomography scan data

Three-dimensional (3D) computer models of the human larynx are useful tools for research and for eventual clinical applications. Recently, computed tomography (CT) scanning and magnetic resonance imaging (MRI) have been used to recreate realistic models of human larynx. In the present study, CT images were used to create computer models of vocal folds, vocal tract, and laryngeal cartilages, and the procedure to create solid models are explained in details. Vocal fold and vocal tract 3D models of healthy and postsurgery larynges during phonation and respiration were created and morphometric parameters were quantified. The laryngeal framework of eight patients was also reconstructed from CT scan images. For each cartilage, morphometric landmarks were measured on the basis of their importance for biomechanical modeling. A quantitative comparison was made between measured values from the reconstructions and those from human excised larynges in literature. The good agreement between these measurements supports the accuracy of CT scan-based 3D models. Generic standard models of the laryngeal framework were created using known features in modeling softwares. They were created based on the morphometric landmark dimensions previously defined, preserving all biomechanically important dimensions. These models are accessible, subject independent, easy to use for computational simulations, and make the comparisons between different studies possible.

Tracheostomaplasty: A surgical method for improving retention of an intraluminal stoma button for hands-free tracheoesophageal speech

BACKGROUND

We describe a minimally invasive surgical technique, tracheostomaplasty, to overcome anatomical deformities of the stoma that preclude successful retention of a stoma button for hands free tracheoesophageal (TE) speech.

METHODS

We conducted a retrospective analysis of 21 patients who underwent tracheostomaplasty after laryngectomy to accommodate an intraluminal valve attachment for hands-free TE speech.

RESULTS

Sixteen men and 5 women (median age, 65 years; median follow-up, 27.7 months) underwent tracheostomaplasty; 6 patients developed a mild cellulitis that required therapy and 5 patients required a minor revision surgery. At last follow-up, 15 (71%) patients successfully achieved hands-free TE speech using an intraluminal stoma button. Three patients only retained the intraluminal device to facilitate digital occlusion. Tracheostomaplasty failed in 3 patients because of granulation tissue formation or stomal stenosis.

CONCLUSIONS

Tracheostomaplasty is a successful technique to improve intraluminal retention of a stoma button for hands-free TE speech in laryngectomy patients.

Anatomical landmarks for endosonography of the larynx

BACKGROUND

A precise knowledge of anatomy is necessary to allow a correct interpretation of sonographic images when investigating a particular region of the body. The objective of the present study was to establish anatomical landmarks for endosonography of the larynx.

METHODS

In an experimental study, a total of 32 normal human larynges were examined endosonographically, and the classical landmarks were correlated to horizontal whole-organ sections of the scanned specimens.

RESULTS

All laryngeal specimens showed a similar and reproducible sonoanatomy, which could be verified consistently on corresponding histological cross sections. Anatomical structures readily identified included the laryngeal framework, the vocal ligament, the vocal muscle, the ventricular fold, the preepiglottic and paraglottic space, and the epiglottis.

CONCLUSIONS

Due to a reproducible sonoanatomy of the larynx, endosonography might be an interesting complementary tool in the diagnostic investigation of laryngeal lesions such as medium-sized tumors, cysts, laryngoceles, and stenoses.

Measurement of cross-sectional dimensions of the cricoid cartilage: a computed tomographic study

OBJECTIVES

We measured the cross-sectional dimensions of the cricoid cartilage and degrees of ossification of the marrow space for designing a cricoid implant.

METHODS

We reviewed 100 age- and sex-matched neck computed tomography scans that were performed at Seoul National University Hospital from 2001 to 2005. Under a standardized computed tomography window setting, the height of the cricoid cartilage marrow and the thickness of the marrow space and the ossified inner and outer cortices were measured by one observer.

RESULTS

The mean height of the cricoid cartilage marrow was 13.6 mm (range, 5.5 to 20.5 mm) in women and 17.5 mm (range, 13.0 to 24.5 mm) in men. The mean thickness of the cricoid cartilage marrow was 3.17 mm (range, 1.22 to 4.75 mm) in women and 5.13 mm (range, 3.42 to 7.60 mm) in men. We also observed that women in general have a higher density of the cricoid marrow than men; 4 women and 1 man had a markedly denser marrow space. There were individual variations in size and density of the cricoid marrow.

CONCLUSIONS

Human adult cricoid cartilages have sufficient marrow space for cricoid implantation. Preoperative evaluation of the size and density of the cricoid marrow is recommended for individual application of the cricoid implant.

Cricotracheal Resection in Nontracheotomized Adults: A Prospective Case Series

Objectives:

Cricotracheal resection is a modern technique of airway reconstruction used in cases of subglottic stenosis. We report a case series of adult, nontracheotomized patients.

Methods:

Fifteen patients with significant subglottic stenosis were identified as presenting with dyspnea and stridor. The stenosis was grade III in 14 cases and grade II in 1 case, according to the Cotton classification. The causes were manifold, with intubation and tracheostomy being the predominant risk factors. Cricotracheal resection was performed in all cases with preoperative and postoperative videotracheoscopy.

Results:

The mean postoperative intubation time was 41.7 hours (11 to 103 hours), and the mean length of stay in the intensive care unit was 2.6 days (3 to 9 days). Videotracheoscopy for reassessment was performed after 96 days (average). In 13 of the 15 patients the subglottic lumen was returned to a normal diameter. In 1 case a recurrent stenosis was managed with repeated endoscopic interventions. One patient died on postoperative day 4 because of a pulmonary embolism. Additional complications consisted of 1 axillary venous embolism, 4 cases of ventilator-associated pneumonia, and 1 case of transient unilateral recurrent nerve palsy that recovered completely.

Conclusions:

Cricotracheal resection is a reliable and versatile technique for the reconstruction of the subglottic airway, almost regardless of the underlying cause. Most complications observed have not been associated directly with the procedure, but reflect the significant comorbidity of the patient population. There seems to be an increased risk for thromboembolic events that may be a consequence of the preoperative immobilization of dyspneic patients.

Mapping of Ki-67 protein distribution on whole organ serial sections of the larynx

CONCLUSIONS

Immunostaining of whole organ serial sections of the larynx is feasible and will allow analysis of cellular alterations in the undisturbed anatomical context of whole organ serial sections of the larynx.

OBJECTIVES

Whole organ serial sections of the larynx have to date been used for conventional macroscopic evaluation of laryngeal tissues. The aim of this study was to establish a protocol for immunohistochemistry of whole organ sections of the larynx.

MATERIALS AND METHODS

Five laryngectomy specimens were obtained during surgery for advanced laryngeal carcinoma. Using a novel method for paraffin embedding, we chose the proliferation marker Ki-67 antigen as a model target for immunoreactivity on serial sections.

RESULTS

We were able to produce whole organ serial sections that could then be immunostained for Ki-67. A complete mapping of proliferating cells throughout the tumour, at the tumour front and in skip lesions was subsequently obtained.

Influence of glottic aperture on the tracheal flow

The extra-thoracic mouth-throat area has a major influence on the aerosol delivery to the proximal or peripheral intra-thoracic airways. To characterize the particle deposition in this area, it is important to investigate first the flow structures in this crucial--in relation to the aerosol deposition--region. The glottis, which is delimited by the vocal cords and therefore has the narrowest passage, generates a laryngeal jet and a reverse flow downstream the glottis. It is generally assumed that the glottis has different shapes and cross-sectional areas at different moments during the respiratory cycle and also depends on the average inspiratory flow rate. Therefore, the influence of a circular glottal aperture, with a cross-sectional area of 90 mm2 and an elliptical and triangular shape, both with an area of 45 mm2, on the flow is investigated. However, the area of the circular aperture is twice as big as the area of the elliptical one, it has almost no influence on the flow structures. On the other hand, the triangular glottal aperture shifts the laryngeal jet in the direction of the posterior wall, and generates two pairs of counter rotating secondary vortices downstream the glottis, where the circular and elliptical only aperture generates one pair of vortices. The difference in pressure drop is more dominated by the cross-sectional area than by the shape of the glottis. This suggests the need for rendering geometry of future upper airway models even more realistic as the appropriate three-dimensional (3D) medical imaging techniques are becoming available.

Immunohistochemistry of whole-organ sections of advanced human laryngeal cancer

Whole-mount sections have been in the interest of laryngologists for long time. The aim of this study was to demonstrate the technical aspects of processing horizontal whole-mount sections of advanced laryngeal cancer specimens after total laryngectomy. Those sections may provide new insights in the biology of laryngeal cancer. Six excised human larynges were block-embedded in paraffine. Serial sections were obtained as thin as 9 mum. Sections were stained by Giemsa and standard immunohistochemistry protocols with commercial antibodies against Cytokeratine5/6, Ki-67, Topoisomerase IIalpha, and p53. Four high-power fields were selected randomly in each section of a surface grid and the percentage of positive tumor cells was noted for each antibody in the respective field. Morphometric surface maps of protein expression were generated for each parameter. The tissues remained intact without major artifacts. Specific characteristics of the tumors were identified after evaluation of the whole-mount sections. Staining of cytokeratine was homogenous, whereas nuclear markers showed a distinct heterogeneity in the respective staining patterns. By analyzation of color-coded fusion images the spatial expression of the respective antibodies could be visualized.

Functional morphology of phonation evaluated by dynamic MRI

The complex anatomy of the larynx is a consequence of its various airway functions. The aim of the present study was to evaluate which anatomical structures of the larynx soft tissues could be defined using MRI, and to investigate the feasibility of using this technique to assess the dynamic functions of the larynx. MRI images of the larynx of six healthy volunteers during speech production were obtained in vivo. The volunteers were asked to breathe out long and deep in order to prolong in a normal voice the emission of the vowels [i] (as in key) and [a] (as in car) and the consonant [ch] (as in ship). We demonstrated the modification of the larynx position, which is high for [i] and low for [a], and the modification of the vocal folds which is adducted and abducted in [i] and kept abducted in [ch]. Dynamic MRI allows the possibility of multiplanar high-resolution imaging. It can provide information about the anatomy of the larynx and, it also has the ability to image moving laryngeal structures and to analyze vocal fold vibrations during phonation.

Individual subject laryngeal dimensions of multiple mammalian species for biomechanical models

OBJECTIVES

This report provides a detailed knowledge base of individual subject laryngeal cartilage dimensions across multiple species to assist researchers in creating subject-specific biomechanical laryngeal models.

METHODS

The raw data from previous laryngeal cartilage studies were grouped by species (for human, canine, and ovine) and by cartilage (arytenoid, thyroid, and cricoid) by means of a previously reported labeling scheme. No animals were sacrificed specifically for the present study.

RESULTS

More than 1,500 measurements from 37 subjects are presented in 15 tables. No comparisons of the average measures were attempted, as they were done in previous studies.

CONCLUSIONS

By means of a database of individual subject dimensions, a laryngeal model could be designed and tested to morph from one subject to the next, predicting subject-specific results of laryngeal function. Eventually, this would lead to modeling patient-specific laryngeal disorders and the prediction of therapeutic outcomes. An electronic downloadable version of the database is made available to assist in this effort.

A three-dimensional model of vocal fold abduction/adduction

A three-dimensional biomechanical model of tissue deformation was developed to simulate dynamic vocal fold abduction and adduction. The model was made of 1721 nearly incompressible finite elements. The cricoarytenoid joint was modeled as a rocking-sliding motion, similar to two concentric cylinders. The vocal ligament and the thyroarytenoid muscle's fiber characteristics were implemented as a fiber-gel composite made of an isotropic ground substance imbedded with fibers. These fibers had contractile and/or passive nonlinear stress-strain characteristics. The verification of the model was made by comparing the range and speed of motion to published vocal fold kinematic data. The model simulated abduction to a maximum glottal angle of about 31 degrees. Using the posterior-cricoarytenoid muscle, the model produced an angular abduction speed of 405 degrees per second. The system mechanics seemed to favor abduction over adduction in both peak speed and response time, even when all intrinsic muscle properties were kept identical. The model also verified the notion that the vocalis and muscularis portions of the thyroarytenoid muscle play significantly different roles in posturing, with the muscularis portion having the larger effect on arytenoid movement. Other insights into the mechanisms of abduction/adduction were given.

Comparison of human, canine, and ovine laryngeal dimensions

Geometric measurement of the laryngeal skeleton is a fundamental step in laryngeal studies, especially in biomechanical modeling. Traditionally, canine larynges have been used as models of the human larynx because of their similarity in size and gross structure, but the search continues for an alternative model because of the diminishing availability of the canine species for research in the United States. In this report, a revised method for defining and labeling laryngeal framework parameters is proposed. Ovine laryngeal cartilages were measured, and the measurements were compared to those of human and canine cartilages previously reported in the literature. The ovine cricoid, thyroid, and arytenoid cartilages were significantly different from the human and canine cartilages. Also, the lack of a definite border between the true and false vocal folds revealed that the ovine model may not always be suitable for a direct comparison to the human larynx in phonation.