Airway evaluation in obstructive sleep apnea

Characterization of upper airway airflow dynamics in young adults with isolated Robin sequence: An exploratory investigation

Impaired upper airway dimension in adults with Isolated Robin Sequence (IRS) can alter airflow dynamics, increasing the risk of pharyngeal collapse and the onset of obstructive sleep apnea. This study aimed to characterize the upper airways of six young adults (20.83 ± 6.40 years) with IRS, using computational fluid dynamics. Upper airways of six patients were reconstructed using 3D segmentation, generating unstructured hybrid meshes with ≥4 million tetrahedral elements. Flow simulations at 15 l/min were solved using the realizable k-ε model and the finite volume method. Morphophysiological variables assessed were: total airway volumes, minimal cross-sectional areas, average pressure, velocity magnitude, wall shear stress, turbulent kinetic energy (k) production, and resistance. Airway volume corresponded to 29.32 ± 4.65 cm³ and minimal cross-sectional area was 1.00 ± 0.55 cm2. Pressure drop, airway resistance to airflow, velocity of the airflow and turbulent kinetic energy corresponded to 31.341 ± 15.837 Pa, 0.125 ± 0.063 (Pa s/ml), 1.882 ± 0.514 (m/s) and 0.152 ± 0.056 (m2/s2). The total airway volume exhibited a strong negative correlation with airway resistance (-0.899) and the inlet-to-outlet pressure drop (-0.899). The minimal cross-sectional area of the pharynx at the retroglossal level showed a strong negative correlation (-0.912) with the area-weighted average velocity magnitude of the airflow and with k production (-0.924). In conclusion, airway volume reduction and retroglossal obstruction in young adults with IRS are associated with altered fluid flow characteristics, including increased velocity magnitude, pressure drop, resistance, and turbulent kinetic energy production. These changes may increase the effort to breathe and predispose patients to sleep-disordered breathing.

Computational fluid dynamics modelling of human upper airway: A review

BACKGROUND AND OBJECTIVE

Human upper airway (HUA) has been widely investigated by many researchers covering various aspects, such as the effects of geometrical parameters on the pressure, velocity and airflow characteristics. Clinically significant obstruction can develop anywhere throughout the upper airway, leading to asphyxia and death; this is where recognition and treatment are essential and lifesaving. The availability of advanced computer, either hardware or software, and rapid development in numerical method have encouraged researchers to simulate the airflow characteristics and properties of HUA by using various patient conditions at different ranges of geometry and operating conditions. Computational fluid dynamics (CFD) has emerged as an efficient alternative tool to understand the airflow of HUA and in preparing patients to undergo surgery. The main objective of this article is to review the literature that deals with the CFD approach and modeling in analyzing HUA.

METHODS

This review article discusses the experimental and computational methods in the study of HUA. The discussion includes computational fluid dynamics approach and steps involved in the modeling used to investigate the flow characteristics of HUA. From inception to May 2020, databases of PubMed, Embase, Scopus, the Cochrane Library, BioMed Central, and Web of Science have been utilized to conduct a thorough investigation of the literature. There had been no language restrictions in publication and study design of the database searches. A total of 117 articles relevant to the topic under investigation were thoroughly and critically reviewed to give a clear information about the subject. The article summarizes the review in the form of method of studying the HUA, CFD approach in HUA, and the application of CFD for predicting HUA obstacle, including the type of CFD commercial software are used in this research area.

RESULTS

This review found that the human upper airway was well studied through the application of computational fluid dynamics, which had considerably enhanced the understanding of flow in HUA. In addition, it assisted in making strategic and reasonable decision regarding the adoption of treatment methods in clinical settings. The literature suggests that most studies were related to HUA simulation that considerably focused on the aspects of fluid dynamics. However, there is a literature gap in obtaining information on the effects of fluid-structure interaction (FSI). The application of FSI in HUA is still limited in the literature; as such, this could be a potential area for future researchers. Furthermore, majority of researchers present the findings of their work through the mechanism of airflow, such as that of velocity, pressure, and shear stress. This includes the use of Navier-Stokes equation via CFD to help visualize the actual mechanism of the airflow. The above-mentioned technique expresses the turbulent kinetic energy (TKE) in its result to demonstrate the real mechanism of the airflow. Apart from that, key result such as wall shear stress (WSS) can be revealed via turbulent kinetic energy (TKE) and turbulent energy dissipation (TED), where it can be suggestive of wall injury and collapsibility tissue to the HUA.

How might non nutritional sucking protect from sudden infant death syndrome

Epidemiology has identified an association between the use of pacifiers and protection from sudden infant death syndrome (SIDS). The use of pacifiers for SIDS prevention fails to gain adoption partly because there is no widely accepted physiologic mechanism to explain the epidemiologic association. Additionally, the scientific literature available on pacifier use focuses largely on the probable adverse effects. We hypothesize that pacifier use and all other forms of non-nutritional sucking (specifically digit sucking, also known as thumb sucking) is a life saving defense mechanism meant to splint open and stabilize the collapsible portion of the upper airway in infants.The main objective of this review article is to propose a mechanism to explain how pacifiers might help prevent SIDS. If the medical community accepts this mechanism, it can help promote pacifier use by the public and potentially reduce the incidence of SIDS.

High-flow nasal cannula ventilation therapy for obstructive sleep apnea in ischemic stroke patients requiring nasogastric tube feeding: a preliminary study

Obstructive sleep apnea (OSA) is associated with increasing risk of recurrent stroke and mortality. Nasogastric tubes used by dysphagic stroke patients may interfere with nasal continuous positive airway pressure (CPAP) due to air leakage. This study was evaluated the effects and short-term tolerability of high-flow nasal cannula (HFNC) therapy for OSA in stroke patients with nasogastric intubation. The HFNC titration study was performed in post-acute ischemic stroke patients with nasogastric intubation and OSA. Then, participants were treated with HFNC therapy in the ward for one week. Eleven participants (eight males) who were all elderly with a median age of 72 (IQR 67-82) years and a body mass index of 23.5 (IQR 22.0-26.6) completed the titration study. The HFNC therapy at a flow rate up to 50~60 L/min significantly decreased the apnea-hypopnea index from 52.0 events/h (IQR 29.9-61.9) to 26.5 events/h (IQR 3.3-34.6) and the total arousal index from 34.6 (IQR 18.6-42.3) to 15.0 (IQR 10.3-25.4). The oxygen desaturation index was also significantly decreased from 53.0 events/h (IQR 37.0-72.8) to 16.2 events/h (IQR 0.8-20.1), accompanied by a significant improvement in the minimum SpO2 level. Finally, only three participants tolerated flow rates of 50~60 L/minute in one-week treatment period. Conclusively, HFNC therapy at therapeutic flow rate is effective at reducing the OSA severity in post-acute ischemic stroke patients with nasogastric intubation. Owing to the suboptimal acceptance, HFNC might be a temporary treatment option, and CPAP therapy is suggested after the nasogastric tube is removed.