Accuracy improvement of two-dimensional shape reconstruction based on OFDR using first-order differential local filtering.

The accuracy of two-dimensional (2D) shape reconstruction is highly susceptible to fake peaks in the strain distribution measured by optical frequency domain reflectometry (OFDR). In this paper, a post-processing method using first-order differential local filtering is proposed to suppress fake peaks and further improve the accuracy of shape reconstruction. By analyzing the principles of 2D shape reconstruction, an explanation of how fake peaks lead to shape reconstruction errors is provided, along with the introduction of an error evaluation standard. The principle of first-order differential local filtering is presented, and its feasibility is verified by simulation. An OFDR 2D shape reconstruction system is built, with three groups of 2D shape reconstruction experiments carried out, including up bending, down bending and arch bending. The experimental results show that the end errors of the three groups of shape reconstruction are respectively reduced from 2.33%, 2.97%, and 1.07% to 0.25%, 0.78%, and 0.20%, at the shape reconstruction length of 0.5 m. The research demonstrates that the accuracy of OFDR 2D shape reconstruction can be improved by using first-order differential local filtering.

Upper airway flow characteristics of childhood obstructive sleep apnea-hypopnea syndrome.

Revealing the structural morphology and inner flow field of the upper airway is important for understanding obstructive sleep apnea-hypopnea syndrome (OSAHS) incidence phenomena and pathological diagnosis in children. However, prior work on this topic has been focused on adults and the findings cannot be directly extrapolated to children because of different inducing factors. Therefore, this paper employs a simulation method to investigate upper airway flow characteristics of childhood OSAHS. It is found that the Reynold number changes highly throughout the whole upper airway, and the laminar assumption is no longer suitable for low Reynold number flow, which is much unlike classic fluid mechanics. Turbulent models of Standard k-ω and Spalart-Allmaras were developed prior to suggestion. The simulation is validated by experiments with an error of approximately 20%. Additionally, carried out in this analysis is the influence of adenoidal hypertrophy with different narrow levels. The cross-sectional area, flow velocity, pressure drop and volume rate will change greatly when the narrow level is above 64% of the upper airway, which can be a quantitative explanation for medical intervention if adenoid hypertrophy blocks 2/3 of the upper airway in the common clinical judgment of otorhinolaryngology. It is expected that this paper can be a meaningful instruction on OSAHS surgery plan making as well as recovery evaluation postoperatively.

[Analysis of upper airway flow field between obstructive sleep apnea and normal children based on computational fluid dynamics].

Objective:In this study, the characteristics of the upper airway flow field were analyzed by using computational fluid dynamics（CFD）. The study analyze the differences in the upper airway flow field between normal children and children with obstructive sleep apnea（OSA）, and the pathological characteristics of children with OSA were elaborated from the perspective of airway fluid dynamics. Methods:The upper airway models of a normal child and a child with OSA were constructed. The differences in the same inspiration pressure, such as airflow velocity, airflow pattern, ventilation volume, and pressure, were analyzed. To verify CFD results, rhinomanometry was carried out and an experimental bench based 3D technology was also built. Results:The CFD results are consistent with the in vitro 3D model experiments and clinical measurement results. The adenoid area of nasopharynx is only 11.274 mm²of the child with OSA, about 1/6 of that of normal children. At the area of nasopharyngeal in OSA children, the flow velocity increased but the pressure dropped sharply, which was 69.197% of the total pressure drop, and the resistance value was 6.59 times of that of normal children. Streamline of nasopharyngeal is more disorder. Normal children's inspiratory flow was 116.139 mL/s, while OSA children's inspiratory flow was 47.055 mL/s, with a difference rate as high as 59.48%. Conclusion:The airflow of OSA children in nasopharynx is significantly different from that of normal children. The airflow characteristics of upper airway were discussed in detail with the use of CFD, which can help clinicians intuitively understand the abnormal flow behavior of children with OSA.