[The acoustics of the open mastoid cavity (so-called "radical cavity) and its modification by surgical measures. I. Physical principles, experimental studies].
Up to now the importance of the outer ear for the sound transmission is nearly neglected in the otosurgical literature. Nevertheless, surgical procedures can cause severe alterations in the anatomy of the outer ear channel. Necessarily variables which take influence on the acoustic behaviour of the outer ear can get changed by these surgical manipulations. By means of in-situ measurements of the sound-pressure-level near the tympanic membrane the influence of the ear channel/mastoid cavity volume as well as of the size of the outer meatus on the resonance frequency is investigated. In a model of variable volume and several sizes of outer meatus there can be found that the course of resonance-caused sound-pressure augmentation depends on two determining factors: due to the physical-acoustical conditions (Helmholtz-resonator) the peak of the resonance-caused augmentation shifts to lower frequencies the smaller the outer meatus and the larger the volume of the channel/mastoid cavity. Viceversa, an augmentation of the external meatus and an obliteration of the cavity causes a higher resonance frequency. Within values for the volume and the meatal size as can be found in radical cavity surgery the resonance frequency varies in a wide range from 1260 up to 3175 Hz. There is no substantial influence on the amplitude of the sound-pressure augmentation. Measurements undertaken in a temporal bone specimen underline these results: as well as in the model alterations of cavity volume and meatal size lead to partial extensive shiftings of the resonance frequency.(ABSTRACT TRUNCATED AT 250 WORDS)
Hartwein
J
J
Univ.-HNO-Klinik, Hamburg-Eppendorf.
D000162:Acoustics; D004424:Ear Canal / Q000503:physiopathology / Q000601:surgery; D006314:Hearing Loss, Conductive / Q000503:physiopathology*; D006801:Humans; D008416:Mastoid / Q000503:physiopathology / Q000601:surgery*; D008953:Models, Anatomic; D011183:Postoperative Complications / Q000503:physiopathology*; D013701:Temporal Bone / Q000503:physiopathology / Q000601:surgery