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

The Effect of an Increasing Subglottal Stenosis Constriction That Extends From the Vocal Folds to the Inferior Border of the Cricoid Cartilage

Acquired subglottal stenosis is an unpredicted complication that can occur in some patients who have undergone prolonged endotracheal intubation. It is a narrowing of the airway at the level of the cricoid cartilage that can restrict airflow and cause breathing difficulty. Stenosis is typically treated with endoscopic airway dilation, with some patients experiencing multiple recurrences. The study highlights the potential of computational fluid dynamics as a noninvasive method for monitoring subglottic stenosis, which can aid in early diagnosis and surgical planning. An anatomically accurate human laryngeal airway model was constructed from computerized tomography (CT) scans. The subglottis cross-sectional area was narrowed systematically using ≈10% decrements. A quadratic profile was used to interpolate the transformation of the airway geometry from its modified shape to the baseline geometry. The numerical results were validated by static pressure measurements conducted in a physical model. The results show that airway resistance follows a squared ratio that is inversely proportional to the size of the subglottal opening (R∝A-2). The study found that critical constriction occurs in the subglottal region at 70% stenosis (upper end of grade 2). Moreover, removing airway tissue below 40% stenosis during surgical intervention does not significantly decrease airway resistance.

Long-Term Non-invasive Ventilation in Children With Down Syndrome: A Systematic Review

Context

Children with Down syndrome are at risk for obstructive sleep apnea, which may not be resolved by adenotonsillecotmy, as well as other respiratory disorders that may impact breathing during sleep. Long-term non-invasive ventilation, including continuous and bilevel positive airway pressure delivery, is an alternate treatment strategy.

Objective

To assess the use and outcomes of long-term non-invasive ventilation in children with Down syndrome including comparison to other children using long-term non-invasive ventilation.

Data Sources

The search strategy for the scoping review used Medical Subject Headings (MeSH) and free-text terms for "child" and "non-invasive ventilation." MEDLINE (Ovid), Embase (Ovid), CINAHL (Ebsco), Cochrane Library (Wiley), and PubMed databases were searched (1990-2021).

Study Selection

The scoping review results were searched to identify studies including data on at least three children with Down Syndrome using long-term non-invasive ventilation.

Data Extraction

Study characteristics, subject characteristics, technology type, and outcome measurements were extracted.

Results

A total of 28 articles included 543 children with Down syndrome using long-term non-invasive ventilation. Children with Down syndrome accounted for 18% of children using long-term non-invasive ventilation. Data on efficacy, feasibility, and adherence in children with Down syndrome are comparable to other children. Children with Down syndrome may have greater difficulty initiating long-term non-invasive ventilation, longer time to establish use, and a higher rate of inability to establish use. Outcome data is limited but suggest favorable impact on cardiac function and attention.

Limitations

Articles related to long-term non-invasive ventilation use in adolescents and young adults may have been excluded.

Conclusions

Children with Down syndrome make up a significant portion of the population of children using long-term non-invasive ventilation. While there is more limited data available with respect to the use and outcomes for children with Down syndrome compared to the other children, long-term non-invasive ventilation is an effective and well-tolerated therapy with no clear differences in the use or outcomes for children with Down syndrome. Additional work is needed to understand potential challenges around establishing long-term non-invasive ventilation use in children with Down syndrome.

Systematic Review Registration

https://www.crd.york.ac.uk/prospero/display_record.php?RecordID=206533, identifier: CRD206533.

Sleep disorders in Down syndrome: a systematic review

BACKGROUND

Sleep disorders are commonly observed in children with Down syndrome (DS) and can lead to significant behavioral and cognitive morbidities in these individuals.

OBJECTIVE

To perform a systematic review evaluating sleep disorders in individuals with DS.

METHODS

Search strategies were based on combinations of keywords: "Down syndrome"; "trisomy 21"; "sleep disorders"; "dyssomnias"; "sleep apnea"; "obstructive"; "sleeplessness"; "insomnia"; "parasomnias"; and "excessive daytime sleepiness". PubMed and Science Direct were used. Only original studies and retrospective reviews in English published between January 2011 and March 2021 were included.

RESULTS

52 articles were included, most of them involving children and adolescents under 18 years of age. The main sleep disorder associated with DS was obstructive sleep apnea (OSA). Some studies reported the presence of cognitive dysfunction in patients with DS and sleep-disordered breathing, and few have been found about parasomnia, insomnia, and daytime sleepiness in these patients. Movement disorders and unusual postures during sleep may be related to disordered sleep breathing in DS. The main treatment options for OSA are continuous positive airway pressure therapy (CPAP), surgery, and weight control. Computational modeling associated with MRI has been used to plan surgical interventions in these patients.

CONCLUSIONS

Individuals with DS are at high risk of developing sleep-related breathing disorders. The main sleep disorder associated with DS was OSA. The presence of sleep-disordered breathing contributes to a worsening of cognitive function in patients with DS.

Predicting critical closing pressure in children with obstructive sleep apnea using fluid-structure interaction

Surgical treatment of obstructive sleep apnea (OSA) in children requires knowledge of upper airway dynamics, including the closing pressure (Pcrit), a measure of airway collapsibility. We applied a flow-structure interaction (FSI) computational model to estimate Pcrit in patient-specific upper airway models obtained from magnetic resonance imaging (MRI) scans. We sought to examine the agreement between measured and estimated Pcrit from FSI models in children with Down syndrome. We hypothesized that the estimated Pcrit would accurately reflect measured Pcrit during sleep and therefore reflect the severity of OSA as measured by the obstructive apnea-hypopnea index (AHI). All participants (n = 41) underwent polysomnography and sedated sleep MRI scans. We used Bland-Altman plots to examine the agreement between measured and estimated Pcrit. We determined associations between estimated Pcrit and OSA severity, as measured by AHI, using regression models. The agreement between passive and estimated Pcrit showed a fixed bias of -1.31 [confidence interval (CI) = -2.78, 0.15] and a nonsignificant proportional bias. A weaker agreement with active Pcrit was observed. A model including AHI, gender, an interaction term for AHI, and gender and neck circumference explained the largest variation (R2 = 0.61) in the relationship between AHI and estimated Pcrit (P < 0.0001). Overlap between the areas of the airway with the lowest stiffness, and areas of collapse on dynamic MRI, was 77.4 ± 30% for the nasopharyngeal region and 78.6 ± 33% for the retroglossal region. The agreement between measured and estimated Pcrit and the significant association with AHI supports the validity of Pcrit estimates from the FSI model.NEW & NOTEWORTHY We present a noninvasive method for estimating critical closing pressure (Pcrit) using fluid-structure interaction (FSI) simulations and magnetic resonance imaging (MRI) scans in patients with obstructive sleep apnea (OSA). We used patient-specific stiffness measures in our FSI model to account for any individual variability in the elasticity of soft tissues surrounding the upper airway. We validated this model by measuring the degree of agreement between measured and estimated Pcrit.

Effect of tube length on the buckling pressure of collapsible tubes

BACKGROUND

The higher incidence of obstructive sleep apnea (OSA) in men than in women has been attributed to the upper airway being longer in men. The Starling resistor is the paradigm biomechanical model of upper airway collapse in OSA where a collapsible tube (representing the pharynx) is located between two rigid tubes (representing the nasal cavity and trachea). While the Starling resistor has been extensively studied due to its relevance to many physiological phenomena, the effect of tube length on tube collapsibility has not been quantified yet.

METHODS

Finite element analysis of a 3-dimensional collapsible tube subjected to a transmural pressure was performed in ANSYS Workbench. The numerical methods were validated with in vitro experiments in a silicone tube whose modulus of elasticity (361 ± 28 kPa) and dimensions (length = 100 mm, diameter = 22.2 mm, and wall thickness = 1.59 mm) were selected so that tube compliance was similar to pharyngeal compliance in humans during sleep. The buckling pressure (transmural pressure at which the tube collapses) was quantified in tubes of three different diameters (10 mm, 16 mm, and 22.2 mm) and ten length-to-diameter ratios (L/D = 4 to 13), while keeping the wall-thickness-to-radius ratio constant at 0.143.

RESULTS

The absolute value of the buckling pressure decreased from 4.7 to 3.3 cmH₂O (461-324 Pa) when L/D increased from 4 to 13. The buckling pressure was nearly independent from tube length for L/D >10.

CONCLUSIONS

Our finding that longer tubes are more collapsible than shorter tubes is consistent with the higher incidence of obstructive sleep apnea in males than females.

Detailed evaluation of the upper airway in the Dp(16)1Yey mouse model of Down syndrome

A high prevalence of obstructive sleep apnea (OSA) has been reported in Down syndrome (DS) owing to the coexistence of multiple predisposing factors related to its genetic abnormality, posing a challenge for the management of OSA. We hypothesized that DS mice recapitulate craniofacial abnormalities and upper airway obstruction of human DS and can serve as an experimental platform for OSA research. This study, thus, aimed to quantitatively characterize the upper airway as well as craniofacial abnormalities in Dp(16)1Yey (Dp16) mice. Dp16 mice demonstrated craniofacial hypoplasia, especially in the ventral part of the skull and the mandible, and rostrally positioned hyoid. These changes were accompanied with a shorter length and smaller cross-sectional area of the upper airway, resulting in a significantly reduced upper airway volume in Dp16 mice. Our non-invasive approach, a combination of computational fluid dynamics and high-resolution micro-CT imaging, revealed a higher negative pressure inside the airway of Dp16 mice compared to wild-type littermates, showing the potential risk of upper airway collapse. Our study indicated that Dp16 mice can be a useful model to examine the pathophysiology of increased upper airway collapsibility of DS and to evaluate the efficacy of therapeutic interventions for breathing and sleep anomalies.

Diagnostic techniques and surgical outcomes for persistent pediatric obstructive sleep apnea after adenotonsillectomy: A systematic review and meta-analysis

OBJECTIVE

To evaluate the efficacy of upper airway surgery for children with persistent obstructive sleep apnea after adenotonsillectomy and to assess sleep study outcomes when Drug Induced Sleep Endoscopy, Cine MRI, or other imaging procedure is performed to assist in identifying the location of obstruction and planning surgery.

METHODS

Systematic review and meta-analysis was performed. Inclusion criteria was English-language studies with original data including pediatric patients with persistent OSA after T&A. Exclusion criteria included case reports and lack of pre and post-operative sleep study data. Data Sources were PubMed, Cochrane Central, and Embase from 2000 to 2018. PRISMA standards were followed for the selection and review of articles. The Newcastle-Ottawa Quality Assessment scale was used to score the quality of evidence of the studies. All manuscripts were reviewed independently by two investigators. Primary outcome measures were apnea-hypopnea index and minimum oxygen saturation. Data was pooled using a random-effects model.

RESULTS

Of the 1902 abstracts identified, 11 studies (214 patients) met inclusion criteria for systematic review, 5 with Drug Induced Sleep Endoscopy as the diagnostic technique, 4 with Cine MRI, and 2 with MRI/CT. All studies were case series. Most subjects had syndromic comorbidities and/or obesity. Ten studies (198 patients) were included in the meta-analysis. Overall, there was a change in apnea hypopnea index of -6.51 (95% CI, -8.17 to - 4.85; p < 0.001) and an increase in minimum oxygen saturation by 3.24% (95% CI, 1.49%-4.98%; p < 0.001) following surgical intervention. Both Drug Induced Sleep Endoscopy and Cine MRI directed surgeries resulted in significant improvement in sleep study parameters. The two techniques could not be directly compared due to significant differences in co-morbidity rates between patients.

CONCLUSIONS

Surgery for pediatric persistent obstructive sleep apnea improves apnea hypopnea index and minimum oxygen saturation but does not resolve the disease. This is true when both Drug Induced Sleep Endoscopy and Cine MRI findings were used to direct surgery.

How design characteristics of tracheostomy tubes affect the cannula and tracheal flows

OBJECTIVES

The aim of this study was to perform computational simulations of airflow within an anatomically accurate model of an adult trachea in different tracheostomy tube designs. We hypothesized that tracheal airflow in patients is significantly influenced by the geometry and size of these devices.

METHODS

The three-dimensional (3D) geometry of the trachea was reconstructed using computed tomography scans for an adult with no history of lung disease. 3D models of four cuffed tube designs, namely Tracoe, Portex, and Shiley Proximal and Distal tracheostomy tubes were generated using geometric modeling software. Transient simulations of airflow in the tube-airway assembly were performed for each tube using computational fluid dynamics (CFD).

RESULTS

Airflow velocity was higher for the Shiley tubes compared with Portex and Tracoe tubes. For all designs, the largest magnitude of inspiratory airflow turbulence was obtained midway in the trachea. The work of breathing, quantified by the resistance of the tracheostomy tube, was lowest for Tracoe. Maximum airway wall shear stress (WSS), defined as flow-induced frictional forces, occurred at the same spatial location in all cases. Low inspiratory WSS at the carina and high expiratory airway WSS at the cuff-airway interface were observed for the Tracoe and Portex tubes.

CONCLUSION

Our CFD model offers a promising approach not only for choosing a tracheostomy tube for a patient but for improving existing tracheostomy tube designs.

LEVEL OF EVIDENCE

NA Laryngoscope, 129:1791-1799, 2019.

Upper airway reconstruction using long-range optical coherence tomography: Effects of airway curvature on airflow resistance

OBJECTIVES

Adenotonsillectomy (AT) is commonly used to treat upper airway obstruction in children, but selection of patients who will benefit most from AT is challenging. The need for diagnostic evaluation tools without sedation, radiation, or high costs has motivated the development of long-range optical coherence tomography (LR-OCT), providing real-time cross-sectional airway imaging during endoscopy. Since the endoscope channel location is not tracked in conventional LR-OCT, airway curvature must be estimated and may affect predicted airway resistance. The study objective was to assess effects of three realistic airway curvatures on predicted airway resistance using computational fluid dynamics (CFD) in LR-OCT reconstructions of the upper airways of pediatric patients, before and after AT.

METHODS

Eight subjects (five males, three females, aged 4-9 years) were imaged using LR-OCT before and after AT during sedated endoscopy. Three-dimensional (3D) airway reconstructions included three airway curvatures. Steady-state, inspiratory airflow simulations were conducted under laminar conditions, along with turbulent simulations for one subject using the k-ω turbulence model. Airway resistance (pressure drop/flow) was compared using two-tailed Wilcoxon signed rank tests.

RESULTS

Regardless of the airway curvatures, CFD findings corroborate a surgical end-goal with computed post-operative airway resistance significantly less than pre-operative (P < 0.01). The individual resistances did not vary significantly for different airway curvatures (P > 0.25). Resistances computed using turbulent simulations differed from laminar results by less than ∼5%.

CONCLUSIONS

The results suggest that reconstruction of the upper airways from LR-OCT imaging data may not need to account for airway curvature to be predictive of surgical effects on airway resistance. Lasers Surg. Med. 51:150-160, 2019. © 2018 Wiley Periodicals, Inc.

Otolaryngologic management of Down syndrome patients: what is new?

PURPOSE OF REVIEW

The management of children with Down syndrome as it pertains to the otolaryngologist continues to evolve. Obstructive sleep apnea (OSA) has dominated the recent literature, but other topics including hearing loss, swallowing, and perioperative considerations are also reported.

RECENT FINDINGS

The prevalence of OSA in children with Down syndrome ranges from 57 to 73% in certain cohorts, and, whereas adentonsillectomy can decrease Apnea-Hypopnea Index, up to 80% may have persistent OSA. Surgical techniques involving reduction of the base of tongue are effective for those who fail adenotonsillectomy, and it is expected that drug-induced sleep endoscopy may improve outcomes. New technology is also on the horizon that can assist with diagnosis and treatment including computational modelling and upper airway stimulation. Children with Down syndrome may not respond to medical management of eustachian tube dysfunction as well as normally developing children. In addition, there is a high prevalence of inner ear anomalies, increasing the risk for sensorineural hearing loss.

SUMMARY

Questions remain pertinent to the otolaryngologist regarding the ideal management of children with Down syndrome. Additional studies are necessary, to optimize understanding and treatment of this complex population, in particular as opportunities develop with technological advances.

Trends in management of obstructive sleep apnea in pediatric patients with Down syndrome

INTRODUCTION

Residual obstructive sleep apnea (OSA) after adenotonsillectomy (T&A) is a common problem in children with Down Syndrome (DS). Our objective was to describe trends in surgical and medical management of OSA in pediatric patients with DS, and to present an algorithmic approach to managing these children.

METHODS

Retrospective case series of children with DS seen at a tertiary care medical center between 1/2008-6/2016 who underwent polysomnography (PSG) after having a T&A performed for sleep disordered breathing (SDB).

RESULTS

Sixty-five patients met inclusion criteria. The mean age at T&A was 4.8 years and 52.0% were male. The mean apnea-hypopnea index (AHI) was 23.2 events/hour for patients who had pre-T&A PSGs. The mean AHI was 10.7 events/hour after T&A. Twenty-three patients (35.4%) underwent at least one additional surgical procedure after T&A; 5 (7.7%) patients had ≥ two additional procedures. The most common additional surgical procedures were revision adenoidectomies (n = 8) and lingual tonsillectomies (n = 13). Fifteen (23.1%) patients underwent at least one drug-induced sleep endoscopy (DISE) to help direct selection of surgical site/s.

CONCLUSIONS

Residual OSA is common after T&A in children with Down syndrome and can be managed by additional surgical interventions in many instances with successful reduction of the AHI. DISE has become part of a standard algorithm for managing persistent OSA in children with Down syndrome after T&A.

Modeling congenital nasal pyriform aperture stenosis using computational fluid dynamics

OBJECTIVES

Congenital nasal pyriform aperture stenosis (CNPAS) is a rare cause of airway obstruction in the neonate. Computational airway modeling has not been done in neonates and young infants to understand the impact of stenosis on functional nasal airflow. In this study, we 1) applied computational fluid dynamics (CFD) model to the airway of a neonate with CNPAS and 2) compare airflow dynamics of a normal and CNPAS airway.

METHODS

Three-dimensional models of the nasal airway of a normal neonate and a neonate with CNPAS were created using computed tomography scans of the facial bones. Measured anatomic parameters included volume, surface area, and cross-sectional area. CFD simulation was then performed. Simulated flow parameters included pressure, average velocity, and resistance.

RESULTS

The neonate with CNPAS had a lesser volume (2.74 cm³ vs. 4.50 cm³) and surface area (18.8 cm² vs. 45.5 cm²) than the normal airway. The CNPAS airway had a lesser bilateral cross-sectional area and average cross-sectional velocity throughout the length of the model. While there is a large pressure drop in the normal airway immediately after the entry point, the pressure drop in the CNPAS airway occurs more posteriorly. The total nasal resistance was approximately eight-fold greater in the CNPAS airway than the normal.

CONCLUSIONS

CFD analysis can be performed on airways of neonates with nasal obstruction, such as in CNPAS. A CFD model may help characterize severity of airway obstruction as it can predict the three-dimensional pattern of airflow. Determining the role of CFD in clinical management of CNPAS requires further investigation.

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.

The Role of Functional Respiratory Imaging in Treatment Selection of Children With Obstructive Sleep Apnea and Down Syndrome

STUDY OBJECTIVES

The complexity of the pathogenesis of obstructive sleep apnea (OSA) in children with Down syndrome (DS) is illustrated by a prevalence of residual OSA after adenotonsillectomy. The aim of this study was to investigate whether upper airway imaging combined with computation fluid dynamics could characterize treatment outcome after adenotonsillectomy in these children.

METHODS

Children with DS and OSA were prospectively included. All children underwent an evaluation of the upper airway and an ultra-low dose computed tomography scan of the upper airway before adenotonsillectomy. The upper airway tract was extracted from the scan and combined with computational fluid dynamics. Results were evaluated using control polysomnography after adenotonsillectomy.

RESULTS

Thirty-three children were included: 18 boys, age 4.3 ± 2.3 years, median body mass index z-score 0.6 (-2.9 to 3.0), and median obstructive apnea-hypopnea index was 15.7 (3-70) events/h. The minimal upper airway cross-sectional area was significantly smaller in children with more severe OSA (P = .03). Nineteen children underwent a second polysomnography after adenotonsillectomy. Seventy-nine percent had persistent OSA (obstructive apneahypopnea index > 2 events/h). A greater than 50% decrease in obstructive apnea-hypopnea index was observed in 79% and these children had a significantly higher volume of the regions below the tonsils.

CONCLUSIONS

This is the first study to characterize treatment outcome in children with DS and OSA using computed tomography upper airway imaging. At baseline, children with more severe OSA had a smaller upper airway. Children with a less favorable response to adenotonsillectomy had a smaller volume of regions below the tonsils, which could be due to enlargement of the lingual tonsils, glossoptosis, or macroglossia.

COMMENTARY

A commentary on this article appears in this issue on page 501.