Ronen Ofri, Geal-Dor Miriam, Kaufmann-Yehezkely Michal, Perez Ronen, Chordekar Shai, Adelman Cahtia, Sohmer Haim
Department of Otorhinolaryngology/Head & Neck Surgery, Hebrew University School of Medicine-Hadassah Medical Center, Jerusalem 91120, Israel.
Speech & Hearing Center, Hebrew University School of Medicine-Hadassah Medical Center, Jerusalem 91120, Israel.
J Am Acad Audiol. 2017 Feb;28(2):152-160. doi: 10.3766/jaaa.16036.
Hearing can be induced not only by airborne sounds (air conduction [AC]) and by the induction of skull vibrations by a bone vibrator (osseous bone conduction [BC]), but also by inducing vibrations of the soft tissues of the head, neck, and thorax. This hearing mode is called soft tissue conduction (STC) or nonosseous BC.
This study was designed to gain insight into the mechanism of STC auditory stimulation.
Fluid was applied to the external auditory canal in normal participants and to the mastoidectomy common cavity in post-radical mastoidectomy patients. A rod coupled to a clinical bone vibrator, immersed in the fluid, delivered auditory frequency vibratory stimuli to the fluid. The stimulating rod was in contact with the fluid only. Thresholds were assessed in response to the fluid stimulation.
Eight ears in eight normal participants and eight ears in seven post-radical mastoidectomy patients were studied.
Thresholds to AC, BC, and fluid stimulation were assessed. The postmastoidectomy patients were older than the normal participants, with underlying sensorineural hearing loss (SNHL). Therefore, the thresholds to the fluid stimulation in each participant were corrected by subtracting his BC threshold, which expresses any underlying SNHL.
Hearing thresholds were obtained in each participant, in both groups in response to the fluid stimulation at 1.0 and 2.0 kHz. The fluid thresholds, corrected by subtracting the BC thresholds, did not differ between the groups at 1.0 kHz. However, at 2.0 kHz the corrected fluid thresholds in the mastoidectomy patients were 10 dB lower (better) than in the normal participants.
Since the corrected fluid thresholds at 1.0 kHz did not differ between the groups, the response to fluid stimulation in the normal participants at least at 1.0 kHz was probably not due to vibrations of the tympanic membrane and of the ossicular chain induced by the fluid stimulation, since these structures were absent in the mastoidectomy patients. In addition, the fluid in the external canal (normal participants) and the absence of the tympanic membrane and the ossicular chain (mastoidectomy patients) induced a conductive hearing loss (threshold elevation to air-conducted sounds coming from the bone vibrator), so that AC mechanisms were probably not involved in the thresholds to the fluid stimulation. In addition, as a result of the acoustic impedance mismatch between the fluid and skull bone, the audio-frequency vibrations induced in the fluid at threshold would probably not lead to vibrations of the bony wall of the meatus, so that hearing by osseous BC is not likely. Therefore, it seems that the thresholds to the fluid stimulation, in the absence of AC and of osseous BC, represent an example of STC, which is an additional mode of auditory stimulation in which the cochlea is activated by fluid pressures transmitted along a series of soft tissues, reaching and exciting the inner ear directly. STC can explain the mechanism of several auditory phenomena.
听觉不仅可由空气传播的声音（气导[AC]）以及骨振动器引起的颅骨振动（骨骨导[BC]）诱发，还可通过诱发头部、颈部和胸部软组织的振动产生。这种听觉模式称为软组织传导（STC）或非骨性骨导。
本研究旨在深入了解STC听觉刺激的机制。
在正常受试者的外耳道以及根治性乳突切除术后患者的乳突切除共同腔中注入液体。一根与临床骨振动器相连的杆浸入液体中，向液体传递听觉频率的振动刺激。刺激杆仅与液体接触。评估对液体刺激的阈值。
对8名正常受试者的8只耳朵和7名根治性乳突切除术后患者的8只耳朵进行了研究。
评估气导、骨导和液体刺激的阈值。乳突切除术后患者比正常受试者年龄大，存在潜在的感音神经性听力损失（SNHL）。因此，通过减去每个受试者的骨导阈值（该阈值表示任何潜在的SNHL）来校正液体刺激的阈值。
两组受试者在1.0 kHz和2.0 kHz频率下对液体刺激均获得了听力阈值。在1.0 kHz时，减去骨导阈值后校正的液体阈值在两组之间没有差异。然而，在2.0 kHz时，乳突切除术后患者校正后的液体阈值比正常受试者低10 dB（更好）。
由于在1.0 kHz时校正后的液体阈值在两组之间没有差异，正常受试者对液体刺激的反应（至少在1.0 kHz时）可能不是由于液体刺激引起的鼓膜和听骨链振动，因为这些结构在乳突切除术后患者中不存在。此外，外耳道中的液体（正常受试者）以及鼓膜和听骨链的缺失（乳突切除术后患者）导致了传导性听力损失（对来自骨振动器的气导声音的阈值升高），因此气导机制可能与液体刺激的阈值无关。此外，由于液体与颅骨之间的声阻抗不匹配，在阈值时液体中诱发的音频振动可能不会导致耳道骨壁的振动，因此骨骨导听力不太可能。因此，似乎在不存在气导和骨骨导的情况下，液体刺激的阈值代表了STC的一个例子，STC是一种额外的听觉刺激模式，其中耳蜗通过沿着一系列软组织传递的液体压力被激活，直接到达并刺激内耳。STC可以解释几种听觉现象的机制。
