Analysis Of Airflow Field In Nasal And Pharyngeal Cavity Before And After Adenoidectomy In Children

Objective:By establishing a three-dimensional numerical model of upper airway including nasal and pharyngeal cavity in healthy children and children with adenoid hypertrophy before and after operation,the changes of air flow field characteristics of the three were compared and analyzed,so as to objectively describe the improvement of children's respiratory obstruction level after adenoidectomy and evaluate the impact on the recovery of nasosinusitis and secretory otitis media.Methods:A case of healthy children and five cases of adenoid hypertrophy with chronic sinusitis and secretory otitis media were scanned by CBCT to obtain the required imaging data.On this basis,the 3D numerical model of upper airway including nasal and pharyngeal cavity was initially established by using three-dimensional reconstruction software Mimics 20.0.Secondly,we use Geomagic studio 12.0 software to smooth the model,construct grid,fit surface and so on.Finally,the mechanical analysis software ANSYS 15.0 was used to numerically simulate and analyze the nasal and pharyngeal airflow fields in healthy children and adenoid hypertrophy patients before and after surgery.Result:1.CBCT scan resultsPreoperative CBCT scan results:Hypertrophic adenoids showed low density of soft tissue,blocking the nasopharynx and posterior nostrils,narrowing the airway of the nasopharynx,showing semilunar or fissure-like changes,and their A/N ratios were greater than 0.7 All patients had mastoid effusion in the middle ear,thickened sinus mucosa,or retention of sinus secretions,and the pharyngeal opening and pharyngeal recess of eustachian tube were not clearly displayed.Results of postoperative CBCT scan:The airway of nasopharynx is spacious,there is no low density shadow of hypertrophic adenoids,the mucosa of paranasal sinuses has basically returned to normal,no secretion is found in paranasal sinuses and middle ear cavity,and the pharyngeal opening and pharyngeal recess of eustachian tube can be seen clearly.The results of scanning were similar to those of healthy children.2.Acoustic impedance test resultsThe results of preoperative acoustic impedance test in children were binaural B-curve,and those of postoperative and healthy children were binaural A-curve.3.Numerical simulation resultsThe structural features of the three-dimensional model of the upper airway:Before adenoidectomy,the pharyngeal opening of eustachian tube was blocked and the airway of nasal cavity and nasopharynx was narrow.After the operation,the pharyngeal opening of eustachian tube was fully exposed and the airway of nasal cavity and nasopharynx was widened.The results of measurement of nasal volume(NV):Preoperative NV was 6.66±1.64cm~3,postoperative NV was 8.84±1.72cm~3,postoperative NV was significantly larger than preoperative NV.By paired t-test,P=0.026<0.05,the difference was statistically significant.Comparative analysis of pressure field:The overall pressure difference of children before operation was large,and the pressure difference decreased after operation.Compared with the posterior nostril and oropharynx,the negative pressure of the adenoid fat area in the nasopharynx is the largest,that is to say,the adenoid fat area in the nasopharynx is always in a relatively negative pressure state compared with the surrounding tissue,and the pressure distribution is the same as that of the healthy children after the relief of the negative pressure state.Comparative analysis of velocity field:There was no obvious order of airflow velocity in the nasal cavity before adenoidectomy,and the order of airflow velocity recovery after adenoidectomy was from high to low:nasal threshold area,total nasal tract,middle nasal tract and lower nasal tract.The nasopharynx was in the high velocity area before the operation,but the high velocity area decreased or disappeared after the operation.The airflow velocity was slow,and the distribution of airflow velocity was the same as that of healthy children.Changes of air flow pattern in nasopharynx:The air flow pattern in nasopharynx was relatively disordered before adenoidectomy,mainly turbulent,and relatively regular after adenoidectomy,which was laminar,the same as that in healthy children.Conclusion:1.In this experiment,by establishing a numerical model of upper airway including nasal and pharyngeal cavity in healthy children and children with adenoid hypertrophy before and after operation,the narrow plane of the upper airway of children with adenoid hypertrophy in nasopharynx was analyzed from the perspective of biomechanics.The airflow field was disordered.After adenoidectomy,the airway of nose and nasopharynx was unobstructed,and the airflow field returned to normal.2.From the analysis of the characteristics of airflow field in the numerical model of nasal and pharyngeal cavity,it is concluded that in addition to the mechanical obstruction of eustachian tube pharyngeal opening,the nasopharynx of children with adenoid hypertrophy has been in a state of relative negative pressure for a long time,which is also an important factor leading to the negative pressure of middle ear cavity and even the occurrence of secretory otitis media.3.After adenoidectomy,the airways of the nasal cavity and nasopharynx are widened,and the airflow field is improved,which is conducive to the drainage of the nasal cavity and sinuses,thereby promoting the recovery of chronic sinusitis and secretory otitis media.