Computational Fluid Dynamics Simulation Of The Upper Airway In Skeletal Class Ⅲ Children With Obstructive Sleep Apnea Hypopnea Syndrome And Hypertrophic Tonsils After Tonsillectomy

ObjectiveIn this study,real three-dimensional models of skeletal Class Ⅲ children with obstructive sleep apnea hypopnea syndrome and hypertrophic tonsils were reconstructed to evaluate the hydrodynamic characteristics of their upper airways before and after tonsillectomy using computational fluid dynamics（CFD）,to reveal the therapeutic mechanism of this therapy on air flow inside upper airway and provide theoretical basis when doctors develop treatment protocols for these children.Materials and methodsIn this study,computed tomography images of 30 skeletal Class Ⅲ children with obstructive sleep apnea hypopnea syndrome and hypertrophic tonsils were collected and these patients were divided into groups A（tonsil grade=Ⅲ,n=18）and B（tonsil grade=Ⅳ,n=12）.Three-dimensional models of their upper airways preoperative（T1）and postoperative（T2）were reconstructed in MIMICS 19.0 and optimized in Geomagic Studio 12.0.Simulations were then conducted using CFD in ANSYS Workbench 18.2.Measuring parameters included area average pressure and area average velocity of representative planes（a:the plane of choana;b:minimum section of nasopharynx;c:the junction of nasopharynx and velopharynx;d:minimum section of velopharynx;e:the junction of velopharynx and glossopharynx;f:the plane of glossopharynx where tonsils are the biggest;g:the junction of glossopharynx and hypopharynx;h:the lowest plane of hypopharynx）,maximal velocity（Vmax）and minimal pressure（Pmin）in plane f,maximal velocity of pharynx（Pharynx-Vmax）,maximal velocity in upper airways（UA-Vmax）,airflow resistance in pharynx（Rpharynx）,pressure drop from choana to plane f（dP）and dP to flow ratio（PQR）.SPSS 22.0 software was used for statistical analysis.ResultsSimulation results showed that area average pressure and area average velocity in planes of subjects in group B decreased in T2 period.The differences of area average pressure in plane a,b,c,d,e,f,g and area average velocity in plane d,e,f,g,h were statistically significant（P<0.05）.The cross-sectional parameters in group A also showed a downward trend from T1 to T2.The difference of area average pressure in plane b was statistically significant（P<0.05）.For Vmax,Pmin,Pharynx-Vmax,UA-Vmax,Rpharynx,dP and PQR,the differences of subjects in group B were statistically significant（P<0.05）from T1 to T2,while those in group A were not significant（P>0.05）.The differences of all measuring parameters in groups A and B were statistically significant（P<0.05）at T1,but not significant（P>0.05）at T2.ConclusionFrom the point of CFD,tonsillectomy could change hydrodynamic characteristics significantly in skeletal Class Ⅲ OSAHS children with grade Ⅳ tonsils hypertrophy,while the same therapy could not influence those with grade Ⅲ hypertrophy.