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

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

Evaluating the biomechanical characteristics of cuffed-tracheostomy tubes using finite element analysis.

The objective of this study was to perform finite element analysis (FEA) of cuff inflation within an anatomically accurate model of an adult trachea in four different cuffed-tracheostomy tube designs. The leakage quantified by the distance between the cuff and trachea was largest for the Tracoe cuff and smallest for the Portex cuff. The smooth muscle stresses were greatest for the Portex and least for the Distal cuff, respectively. The proposed FEA model offers a promising approach to virtually evaluate the sealing efficacy of cuffed-tracheostomy tubes and the tracheal wall stresses induced by cuff inflation, prior to application.

Aortic growth rates are not increased in Turner syndrome-a prospective CMR study.

BACKGROUND: Aortic disease is a key determinant of outcomes in Turner syndrome (TS). The present study characterized aortic growth rates and outcomes over nearly a decade in adult women with TS. METHODS AND RESULTS: Prospective observational study assessing aortic diameters twice with cardiovascular magnetic resonance imaging in women with TS [N = 91; mean follow-up 8.8 ± 3.3 (range 1.6-12.6) years] and healthy age-matched female controls [N = 37; mean follow-up 6.7 ± 0.5 (range 5.9-8.1) years]. Follow-up also included aortic outcomes and mortality, antihypertensive treatment and ambulatory blood pressure. Aortic growth rates were similar or smaller in TS, but the variation was larger. The proximal aorta in TS grew by 0.20 ± 0.26 (mid-ascending) to 0.32 ± 0.36 (sinuses) mm/year. This compared to 0.26 ± 0.14 (mid-ascending) and 0.32 ± 0.17 (sinuses) mm/year in the controls. During 799 years at risk, 7 suffered an aortic outcome (1 aortic death, 2 aortic dissections, 2 aortic interventions, 2 surgical aortic listings) with further 2 aortic valve replacements. At baseline, two women were excluded. One died during subacute aortic surgery (severe dilatation) and one had a previously undetected type A dissection. The combined aortic outcome rate was 1126 per 100 000 observation years. The aortic and all-cause mortality rates were 1 per 799 years (125 deaths per 100 000 observation years) and 9 per 799 years (1126 deaths per 100 000 observation years). Aortic growth patterns were particularly perturbed in bicuspid aortic valves (BAV) and aortic coarctation (CoA). CONCLUSION: Aortic growth rates in TS are not increased. BAVs and CoA are major factors that impact aortic growth. Aortic outcomes remain a concern.

Biomechanics of the soft-palate in sleep apnea patients with polycystic ovarian syndrome.

Highly compliant tissue supporting the pharynx and low muscle tone enhance the possibility of upper airway occlusion in children with obstructive sleep apnea (OSA). The present study describes subject-specific computational modeling of flow-induced velopharyngeal narrowing in a female child with polycystic ovarian syndrome (PCOS) with OSA and a non-OSA control. Anatomically accurate three-dimensional geometries of the upper airway and soft-palate were reconstructed for both subjects using magnetic resonance (MR) images. A fluid-structure interaction (FSI) shape registration analysis was performed using subject-specific values of flow rate to iteratively compute the biomechanical properties of the soft-palate. The optimized shear modulus for the control was 38 percent higher than the corresponding value for the OSA patient. The proposed computational FSI model was then employed for planning surgical treatment for the apneic subject. A virtual surgery comprising of a combined adenoidectomy, palatoplasty and genioglossus advancement was performed to estimate the resulting post-operative patterns of airflow and tissue displacement. Maximum flow velocity and velopharyngeal resistance decreased by 80 percent and 66 percent respectively following surgery. Post-operative flow-induced forces on the anterior and posterior faces of the soft-palate were equilibrated and the resulting magnitude of tissue displacement was 63 percent lower compared to the pre-operative case. Results from this pilot study indicate that FSI computational modeling can be employed to characterize the mechanical properties of pharyngeal tissue and evaluate the effectiveness of various upper airway surgeries prior to their application.

Effect of airflow and material models on tissue displacement for surgical planning of pharyngeal airways in pediatric down syndrome patients.

Pharyngeal narrowing in obstructive sleep apnea (OSA) results from flow-induced displacement of soft tissue. The objective of this study is to evaluate the effect of airflow parameters and material model on soft tissue displacement for planning surgical treatment in pediatric patients with OSA and Down syndrome (DS). Anatomically accurate, three-dimensional geometries of the pharynx and supporting tissue were reconstructed for one pediatric OSA patient with DS using magnetic resonance images. Six millimeters of adenoid tissue was virtually removed based on recommendations from the surgeon, to replicate the actual adenoidectomy. Computational simulations of flow-induced obstruction of the pharynx during inspiration were performed using patient-specific values of tissue elasticity for pre and post-operative airways. Sensitivity of tissue displacement to selection of turbulence model, variation in inspiratory airflow, nasal airway resistance and choice of non-linear material model was evaluated. The displacement was less sensitive to selection of turbulence model (10% difference) and more sensitive to airflow rate (20% difference) and nasal resistance (30% difference). The sensitivity analysis indicated that selection of Neo-Hookean, Yeoh, Mooney-Rivlin or Gent models would result in identical tissue displacements (less than 1% difference) for the same flow conditions. Change in pharyngeal airway resistance between the rigid and collapsible models was nearly twice for the pre-operative case as compared to the post-operative scenario. The tissue strain at the site of obstruction in the velopharyngeal airway was lowered by approximately 84% following surgery. Inclusion of tissue elasticity resulted in better agreement with the actual surgical outcome compared to a rigid wall assumption, thereby emphasizing the importance of pharyngeal compliance for guiding treatment in pediatric OSA patients.

Computational Modeling of Airway Obstruction in Sleep Apnea in Down Syndrome: A Feasibility Study.

Current treatment options are successful in 40% to 60% of children with persistent obstructive sleep apnea after adenotonsillectomy. Residual obstruction assessments are largely subjective and do not clearly define multilevel obstruction. We endeavor to use computational fluid dynamics to perform virtual surgery and assess airflow changes in patients with Down syndrome and persistent obstructive sleep apnea. Three-dimensional airway models were reconstructed from respiratory-gated computed tomography and magnetic resonance imaging. Virtual surgeries were performed on 10 patients, mirroring actual surgeries. They demonstrated how surgical changes affect airflow resistance. Airflow and upper airway resistance was calculated from computational fluid dynamics. Virtual and actual surgery outcomes were compared with obstructive apnea-hypopnea index values. Actual surgery successfully treated 6 of 10 patients (postoperative obstructive apnea-hypopnea index <5). In 8 of 10 subjects, both apnea-hypopnea index and the calculated upper airway resistance after virtual surgery decreased as compared with baseline values. This is a feasibility and proof-of-concept study. Further studies are needed before using these techniques in surgical planning.

The effects of hydrodynamic stretch on the flame propagation enhancement of ethylene by addition of ozone.

The effect of O(3) on C(2)H(4)/synthetic-air flame propagation at sub-atmospheric pressure was investigated through detailed experiments and simulations. A Hencken burner provided an ideal platform to interrogate flame speed enhancement, producing a steady, laminar, nearly one-dimensional, minimally curved, weakly stretched, and nearly adiabatic flame that could be accurately compared with simulations. The experimental results showed enhancement of up to 7.5% in flame speed for 11 000 ppm of O(3) at stoichiometric conditions. Significantly, the axial stretch rate was also found to affect enhancement. Comparison of the flames for a given burner exit velocity resulted in the enhancement increasing almost 9% over the range of axial stretch rates that was investigated. Two-dimensional simulations agreed well with the experiments in terms of flame speed, as well as the trends of enhancement. Rate of production analysis showed that the primary pathway for O(3) consumption was through reaction with H, leading to early heat release and increased production of OH. Higher flame stretch rates resulted in increased flux through the H+O(3) reaction to provide increased enhancement, due to the thinning of the flame that accompanies higher stretch, and thus results in decreased distance for the H to diffuse before reacting with O(3).

Planning human upper airway surgery using computational fluid dynamics.

The study advances the idea of using computational fluid dynamics in the process of planning surgical treatment modalities for patients with obstructive airway disorders. It is hypothesized that the a priori knowledge of the functional outcome of surgical intervention on the flow and airway resistance can guide the surgeon in choosing an effective surgical strategy. Computed tomography images spanning the respiratory tract of an adult patient with a combined glottic and subglottic stenosis are used to reconstruct three-dimensional geometrical models of the airway. Computational fluid dynamics is used to obtain airway flow patterns during inspiration and expiration in these models. Numerical predictions about flow velocity, pressure distribution on the airway lumen, wall shear stress, and airway resistance are obtained so that the relevance of each individual stenotic level is quantified. Four different virtual surgeries in different combinations are assessed in order to remedy the constricted airway. The virtual surgery based airway models are evaluated by comparisons with the pre-treatment flow modeling results. The predicted numerical data revealed that the removal of the constriction at the level of the vocal folds will have the most significant effect on the airway resistance. The flow simulations offer a quantitative method of evaluating the airway resistance in patients with combined glottic and subglottic stenoses. Predictions of airway resistances and other numerical calculations from different virtual surgeries give additional inputs for the surgeon, in deciding the most appropriate surgery on a case-by-case basis.

An adverse effect of positive airway pressure on the upper airway documented with magnetic resonance imaging.

IMPORTANCE: Positive pressure air is used during basic life support to provide respirations and applied as continuous positive airway pressure to maintain a patent airway during sleep or anesthesia. These functions are more critical in children with obstructive sleep apnea, who often have smaller airway dimensions and increased airway collapsibility. OBSERVATIONS: We report 2 cases of boys with Down syndrome and a history of obstructive sleep apnea in whom adverse narrowing of the retroglossal airway is caused by continuous positive airway pressure applied via face mask as documented with magnetic resonance imaging. CONCLUSIONS AND RELEVANCE: Administration of continuous positive airway pressure by means of face mask to patients can result in adverse effects on the airway patency by pushing the tongue posteriorly. Awareness of this effect on patients with open mouths and large tongues, as present in Down syndrome, is important for sleep apnea treatment, anesthesia, and emergency respiratory support. Generalization of our observation is not possible at this time. Additional prospective studies of the effects of continuous positive airway pressure on airway patency in sedated and/or anesthetized children are required to confirm our anecdotal observations.

Patterns in pharyngeal airflow associated with sleep-disordered breathing.

OBJECTIVE: To establish the feasibility of a noninvasive method to identify pharyngeal airflow characteristics in sleep-disordered breathing. METHODS: Four patients with sleep-disordered breathing who underwent surgery or used positive airway pressure devices and four normal healthy controls were studied. Three-dimensional CT imaging and computational fluid dynamics modeling with standard steady-state numerical formulation were used to characterize pharyngeal airflow behavior in normals and pre-and post-treatment in patients. Dynamic flow simulations using an unsteady approach were performed in one patient. RESULTS: The pre-treatment pharyngeal airway below the minimum cross-sectional area obstruction site showed airflow separation. This generated recirculation airflow regions and enhanced turbulence zones where vortices developed. This interaction induced large fluctuations in airflow variables and increased aerodynamic forces acting on the pharyngeal wall. At post-treatment, for the same volumetric flow rate, airflow field instabilities vanished and airflow characteristics improved. Mean maximum airflow velocity during inspiration reduced from 18.3±5.7 m/s pre-treatment to 6.3±4.5 m/s post-treatment (P=0.002), leading to a reduction in maximum wall shear stress from 4.8±1.7 Pa pre-treatment to 0.9±1.0 Pa post-treatment (P=0.01). The airway resistance improved from 4.3±1.4 Pa/L/min at pre-treatment to 0.7±0.7 Pa/L/min at post-treatment (P=0.004). Post-treatment airflow characteristics were not different from normal controls (all P ≥ 0.39). CONCLUSION: This study demonstrates that pharyngeal airflow variables may be derived from CT imaging and computational fluid dynamics modeling, resulting in high quality visualizations of airflow characteristics of axial velocity, static pressure, and wall shear stress in sleep-disordered breathing.

Large eddy simulation of the pharyngeal airflow associated with obstructive sleep apnea syndrome at pre and post-surgical treatment.

Obstructive Sleep Apnea Syndrome (OSAS) is the most common sleep-disordered breathing medical condition and a potentially life-threatening affliction. Not all the surgical or non-surgical OSAS therapies are successful for each patient, also in part because the primary factors involved in the etiology of this disorder are not completely understood. Thus, there is a need for improving both diagnostic and treatment modalities associated with OSAS. A verified and validated (in terms of mean velocity and pressure fields) Large Eddy Simulation approach is used to characterize the abnormal pharyngeal airflow associated with severe OSAS and its interaction with the airway wall in a subject who underwent surgical treatment. The analysis of the unsteady flow at pre- and post-treatment is used to illustrate the airflow dynamics in the airway associated with OSAS and to reveal as well, the changes in the flow variables after the treatment. At pre-treatment, large airflow velocity and wall shear stress values were found at the obstruction site in all cases. Downstream of obstruction, flow separation generated flow recirculation regions and enhanced the turbulence production in the jet-like shear layers. The interaction between the generated vortical structures and the pharyngeal airway wall induced large fluctuations in the pressure forces acting on the pharyngeal wall. After the surgery, the flow field instabilities vanished and both airway resistance and wall shear stress values were significantly reduced.

What can vortices tell us about vocal fold vibration and voice production.

PURPOSE OF REVIEW: Much clinical research on laryngeal airflow has assumed that airflow is unidirectional. This review will summarize what additional knowledge can be obtained about vocal fold vibration and voice production by studying rotational motion, or vortices, in laryngeal airflow. RECENT FINDINGS: Recent work suggests two types of vortices that may strongly contribute to voice quality. The first kind forms just above the vocal folds during glottal closing, and is formed by flow separation in the glottis; these flow separation vortices significantly contribute to rapid closing of the glottis, and hence, to producing loudness and high frequency harmonics in the acoustic spectrum. The second is a group of highly three-dimensional and coherent supraglottal vortices, which can produce sound by interaction with structures in the vocal tract. Present work is also described that suggests that certain laryngeal pathologies, such as asymmetric vocal fold tension, will significantly modify both types of vortices, with adverse impact on sound production: decreased rate of glottal closure, increased broadband noise, and a decreased signal to noise ratio. SUMMARY: Recent research supports the hypothesis that glottal airflow contains certain vortical structures that significantly contribute to voice quality.

Computational modeling of upper airway before and after adenotonsillectomy for obstructive sleep apnea.

Adenotonsillectomy, the first-line surgical treatment for obstructive sleep apnea (OSA) in children, is successful in only 50% of obese children. Computational fluid dynamics tools, which have been applied to differentiate OSA patients from those without OSA based on the airway flow characteristics, can be potentially used to identify patients likely to benefit from surgical intervention. We present computational modeling of the upper airway before and after adenotonsillectomy in an obese female adolescent with OSA. The subject underwent upper airway imaging on a 1.5 Tesla magnetic resonance imaging (MRI) scanner, and three-dimensional airway models were constructed using airway boundary coordinates from cross-sectional MRI scans. Our results using computational simulations indicate that, in an obese child, the resolution of OSA after adenotonsillectomy is associated with changes in flow characteristics that result in decreased pressure differentials across the airway walls and thus lower compressive forces that predispose to airway collapse. Application of such findings to an obese child seeking surgical treatment for OSA can potentially lead to selection of the surgical procedure most likely to result in OSA resolution. Effective intervention for OSA in this high-risk group will result in reduction in morbidity and the public health concerns associated with OSA.