Application Of Computational Fluid Dynamics In The Evaluation Of Upper Airway Obstruction Plane In Patients With Obstructive Sleep Apnea Hypopnea Syndrome

Objective:By establishing a three-dimensional finite element model of the upper airway of adult patients with obstructive sleep apnea hypopnea syndrome（OSAHS）and healthy adults,the static and dynamic characteristics of the upper airway of adult patients with OSAHS and healthy adults were analyzed and compared by computational fluid dynamics（CFD）,and the upper airway obstruction plane was located by the characteristics of the upper airway,To explore the correlation between upper airway characteristics and polysomnography（PSG）indexes in adult OSAHS patients,the effect of turbinate hypertrophy on upper airway airflow in adult OSAHS patients,and the possibility of evaluating the surgical effect of adult OSAHS patients through upper airway airflow characteristics,so as to provide reference and guidance for the diagnosis and treatment of OSAHS.Methods:10 adult OSAHS patients were selected as the experimental group and 5 healthy volunteers as the control group.Both OSAHS experimental group and control group underwent upper airway computed tomography（CT）and PSG.The CT scanning images of the experimental group and control group were imported into mimics 21.0 software for upper airway three-dimensional model reconstruction,and the three-dimensional model was imported into Geomagic studio 2014 software to optimize the three-dimensional model.The three-dimensional model was meshed by HyperMesh 13.0 software to establish a three-dimensional finite element model.Then the numerical simulation of the model is carried out by ANSYS FLUENT software,and the data post-processing is carried out by ANSYS CFD post software.Finally,using the upper airway CT data,upper airway CFD data and PSG data,some representative indexes were selected to compare and analyze the upper airway CT indexes,CFD indexes and PSG indexes between adult OSAHS patients and healthy adults;Correlation analysis of upper airway CT index,CFD index and PSG index in adult OSAHS patients;And adult OSAHS patients were divided into two subgroups according to whether they were accompanied by turbinate hypertrophy,preoperative and postoperative.The CT indexes,CFD indexes and PSG indexes of the upper airway of the two subgroups were compared and analyzed respectively.Index selection includes CT indexes:the distance between the posterior edge of the hard palate and the posterior pharyngeal wall（C1）,the transverse diameter of the nasopharyngeal cavity at the level of the hard palate（C2）,the thickness of the soft palate（C3）,the distance between the horizontal tongue root of the epiglottic tip and the posterior pharyngeal wall（C4）,the distance between the middle of the hyoid bone and the posterior pharyngeal wall at the level of the hyoid bone（C5）,the shortest transverse diameter of the pharyngeal cavity from the hard palate to the hyoid bone level（C6）,the minimum cross-sectional area of the upper airway（CSAmin）,the longitudinal diameter of the pharyngeal cavity at the minimum cross-sectional area of the upper airway（CSA longitudinal）,Transverse diameter（CSA transverse）,longitudinal diameter and transverse diameter ratio（CSA aspect ratio）;CFD indicators:the cross-sectional pressure（P1）,cross-sectional velocity（V1）at the posterior nostril section of the upper airway,the cross-sectional pressure（P2）,cross-sectional velocity（V2）of the pharyngeal cavity at the lower edge of the soft palate,the cross-sectional pressure（P3）,cross-sectional velocity（V3）of the pharyngeal cavity at the level of the epiglottis tip,the cross-sectional pressure（P4）,cross-sectional velocity（V4）of the pharyngeal cavity at the root of the epiglottis,the maximum flow velocity（V max）of the upper airway,and the pressure difference between different sections △P1-2,△P2-3,△P3-4,△P总（△P1-4）,velocity difference between different sections △ V1-2,△V 2-3,△V 3-4,△V 总（△V 1-4）;PSG indexes:sleep apnea hypopnea index（AHI）,lowest peripheral oxygen saturation（LSpO2）and mean peripheral oxygen saturation（MSpO2）.Results:（1）There were significant differences in C1,C3,C6,CSA min,CSA longitudinal,CSA transverse,CSA aspect ratio,V2,V3,|△V1-2|,|△V2-3|,V max,P2,P3,P4,|△P1-2|,|△P2-3|,|△P3-4|,|△P total|,AHI,LSpO2,MSpO2 between adult OSAHS patients and healthy adults.The indexes of C3,CSA aspect ratio,V2,V3,|△V1-2|,｜△V 2-3|,V max,P2,P3,P4,|△P1-2|,|△P2-3|,|△P3-4|,|△P total|,AHI in adult OSAHS patients were higher than those in healthy adults,and the indexes of C1,C6,CSA min,CSA longitudinal,CSA transverse,LSpO2 and MSpO2 in adult OSAHS patients were lower than those in healthy adults;There was no significant difference in C2,C4,C5,V1,V4,|△V3-4|,|△V total|,P1 and other indexes between adult OSAHS patients and healthy adults.The cross-sectional velocity V2 and cross-sectional pressure P2 of palatopharyngeal section in adult OSAHS patients were significantly higher than those of the other three sections.②C6 in adult OSAHS patients was negatively correlated with |△V1-2|;C4 is negatively correlated with |△V3-4|;C2 was negatively correlated with |△P2-3|,LSpO2 and MSpO2;CSA min is negatively correlated with |△P1-2|,|△P3-4|,|△P total|,|△V1-2|,|△V2-3|,V max,|△V total|,CSA min is highly negatively correlated with |△P1-2|,|△P total|,|△V1-2|,|△V2-3|,V max;CSA longitudinal is negatively correlated with |△P1-2|,|△P3-4|,|△P total|,|△V1-2|,|△V2-3|,V max,|△V total|,and CSA longitudinal is highly negatively correlated with V max;CSA transverse is negatively correlated with |△P1-2|,|△P3-4|,|△P total|,|△V1-2|,|△V2-3|,V max;The correlation between other CT indexes,CFD indexes and PSG indexes was not statistically significant.③ There were significant differences in CSA min,CSA longitudinal,CSA transverse,|△P1-2|,|△P2-3|,|△P3-4|,|△P total|,|△V1-2|,|△V2-3|,|△V total|,V max in adult OSAHS patients with or without inferior turbinate hypertrophy.The indexes of |△P1-2|,|△P2-3|,|△P3-4|,|△P total|,|△V1-2|,|△V2-3|,|△V total|,V max in adult OSAHS patients with inferior turbinate hypertrophy were higher than those in adult OSAHS patients without inferior turbinate hypertrophy.The indexes of CSA min,CSA longitudinal and CSA transverse in adult OSAHS patients with inferior turbinate hypertrophy were lower than those in adult OSAHS patients without inferior turbinate hypertrophy;There was no significant difference in C1,C2,C3,C4,C5,C6,CSA aspect ratio,|△V3-4|,AHI,LSpO2 and MSpO2 between adult OSAHS patients with inferior turbinate hypertrophy and adult OSAHS patients without inferior turbinate hypertrophy.④The indexes of CSA min,CSA transverse,LSpO2 and MSpO2 in 3 adult OSAHS patients increased after operation,while the indexes of CSA aspect ratio,P2,P3,V2,Vmax,|△AP1-2|,|△P2-3|,|△V1-2|,|△V2-3|,AHI decreased,and the indexes of P1,P4,V1,V3,V4,|△P3-4|,|△P total|,|△V3-4|,|△V total|,CSA longitudinal increased or decreased.Conclusions:① Compared with healthy adults,the minimum cross-sectional area of the upper airway in adult OSAHS patients is smaller and mostly located in the palatopharyngeal region,while the aspect ratio of the minimum cross-sectional area of the upper airway is larger,suggesting that the transverse collapse of the upper airway may be the potential anatomical mechanism of upper airway stenosis in OSAHS patients in this experimental group;The changes of pressure and gas flow velocity between sections of upper airway in adult OSAHS patients are more severe than those in healthy adults,especially near the palatopharyngeal level.②The smaller the minimum cross-sectional area of the upper airway obstruction plane in patients with OSAHS,the greater the negative pressure and air velocity in the airway at the obstruction site.The air flow in the upper airway has little effect on AHI and blood oxygen.③Nasal obstruction caused by turbinate hypertrophy can aggravate the changes of airway pressure and airflow from posterior nostril level to glossopharynx level in adult OSAHS patients,and reduce the minimum cross-sectional area of upper airway to a greater extent,but has little effect on the changes of pressure and velocity from glossopharynx level to epiglottis root level.④CFD has important guiding significance for the evaluation of the therapeutic effect of OSAHS.Upper airway dilation in adult OSAHS patients can increase the minimum cross-sectional area of the upper airway,reduce the changes of pressure and flow velocity in each section,and improve the severity of the disease and blood oxygen from the level of nostril to the level of glossopharynx.