完壁与开放式乳突根治术后空气传导的有限元模型分析

Finite Element Analysis of the Effects of Canal Wall-up and Canal Wall-down Mastoidectomy on Air Conduction

目的利用有限元模型研究完壁式与开放式乳突根治鼓室成形术对中耳空气传导的影响。方法对新鲜尸头进行解剖,模拟完壁式乳突根治术、开放式乳突根治术、开放式乳突根治术并骨粉填塞三种术式,通过颞骨薄层CT扫描和逆像成型技术建立三种术式的人耳有限元模型;在耳道口施加90 dB SPL声压获得相应的鼓膜脐部和镫骨底板的位移频响曲线,以鼓膜表面施加90 dB SPL声压得到镫骨底板的响应曲线作为基准,通过公式计算三种术腔的等效声压级差值;通过对比三种术式镫骨底板位移的最大响应频率、最大振幅、平均振幅和平均等效声压级差,分析术后中耳空气传导的变化特点。结果三种术式术后镫骨位移在低频段(<1 kHz)基本一致,在中高频段不同容积的术腔其最大振幅所在的频段发生改变,完壁术式最大振幅所在频率为3 kHz左右,最大振幅为1.17×10^(-5)mm,平均振幅为6.95×10^(-6)mm,平均等效声压级差为3.28 dB;开放术式最大振幅所在频率为1.8 kHz左右,最大振幅为1.27×10^(-4)mm,平均振幅为6.59×10^(-6)mm,平均等效声压级差为5.54 dB;开放并填塞骨粉术式最大振幅所在频率介于二者之间,为2~3 kHz,最大振幅为1.04×10^(-5)mm,平均振幅为9.82×10^(-5) mm,平均等效声压级差为4.52 dB。结论乳突根治术开放外耳道使术腔变大、共振频率降低,完壁式、开放式、开放并填塞骨粉三种术式术后中耳空气传导差异较小。

Objective To study the influence of canal wall-up and canal wall-down mastoidectomy on postoperative air conduction with finite element model.Methods The fresh cadaver head was dissected to simulate three kinds of operation:canal wall-up mastoidectomy,canal wall-down mastoidectomy,canal wall-down mastoidectory with bone powder packing.Three kinds of middle ear finite element model were established by temporal bone thin slice CT scanning and inverse image forming technology.Sound pressure of 90 dB SPL was applied at the ear canal entrance,and the corresponding displacement frequency response curves of tympanic membrane and stapes footplate were obtained.Using the response curve of the stapes footplate obtained by applying 90 dB SPL sound pressure on the surface of the tympanic membrane as a reference,the difference of the equivalent sound pressure level of three operation methods was calculated by formula.By comparing the maximum response frequency,the maximum amplitude,the average amplitude and the average equivalent sound pressure level difference of the three kinds of stapes footplate displacement,the characteristics of postoperative sound conduction were analyzed.Results The stapes displacement of the three types of operation was basically the same in the low frequency range(f<1 kHz),but in the middle and high frequency range,the frequency band of the maximum amplitude of the cavity with different volume changed.The maximum amplitude frequency of the closed mastoidectomy was 3 kHz,the maximum amplitude was 1.16681×10^(-5) mm,the average amplitude was 6.95×10^(-6) mm,the average hearing level was 3.28 dB.The maximum amplitude frequency of the open mastoidectomy was about 1.8 kHz,the maximum amplitude was 1.27×10^(-4) mm,the average amplitude was 6.59×10^(-6) mm,the average hearing level was 5.54 dB.The maximum amplitude frequency of the open mastoidectory with packed bone powder was between the two,which was between 1 kHz and 2 kHz.The maximum amplitude was 1.04×10^(-5) mm,the average amplitude was 9.82×10^(-5) mm,and the average hearing level was 4.52 dB.Conclusion Mastoidectomy radically opens the external auditory canal,making the cavity larger and reduces the resonance frequency.There was little difference in the average hearing after the three methods of canal wall-up,canal wall-down,canal wall-down with bone powder packing.