纯音骨导听阈测试的掩蔽问题

目的：通过对一组耳科正常青年人及不同性质的耳聋患者进行韦伯试验(WT)及骨导掩蔽测试，以探讨骨导测试现象的规律，为临床测试提供指导。方法：分别对20例耳科正常青年人及113例有不同性质听力损失的患者进行WT及骨导掩蔽测试。结果：当双耳均无传导障碍时，骨导听阈取决于双耳耳蜗听敏度，WT偏向取决于双耳听敏度之差。不同性质的传导性病变，使不同频段的骨导听阈降低。一耳正常，另耳为传导性聋时，WT3～5个频率偏患耳；另耳为耳蜗性聋且气导耳间差大于40dB时，患耳骨导越边。双耳传导性聋或双耳混合性聋或一耳传导性聋另耳混合性聋，骨导听阈取决于双耳病变的不同性质、不同程度，WT偏向无规律。当双耳骨导听阈正常而气导听阈大于耳间衰减时，则掩蔽无法实施。结论：为避免中枢掩蔽和过度掩蔽的影响，实验发现：①双耳均无传导障碍，且双耳气导听阈之差大于40dB，测优势耳骨导时不需掩蔽，劣势耳骨导听阈越边；②一耳正常、另耳为传导性聋，测试患耳骨导时不需掩蔽；③若双耳存在传导性病变，且骨导听阈正常而气导听阈大于耳间衰减，则掩蔽无法实施，放弃掩蔽测试。

Probe to the bone-conduction phenomenon

OBJECTIVE: To probe into the rule of bone-conduction measurement by testing a group of health young students with normal hearing and groups of case with different diseased ears, in order to provide some instructions for clinical audiometry. METHOD: Subjects included 20 health young students with normal hearing, 113 cases with different hearing loss. We tested all the subjects Weber Test and bone-conduction threshold by masking. RESULT: Weber Test lateralization dependented on the difference of binanural sensitivity when binaural had no conductive impairment. Different conductive impairment improved bone-conduction response at different frequencies. When monaural had conductive impairment and the other ear normal, there were 3-5 octaves WT lateralizated to the diseased ear. When there were binaural conductive impairments, bone-conduction response dependented on the nature and degree of the impairment, WT lost the rule. CONCLUSION: In order to avoid the negative effects of central masking and overmasking, our observations came to the conclusion that some conditions as follow need no masking: (1) There are no conductive impairment binaural, and the air-conduction pure tone threshold (PTT) gap between binaural higer than 40 dB, when we test bone-conduction PTT of better ear, we need no masking, as for the poor ear, it's bone conduction will come cross to the contralateral ear. (2) When one ear normal and the other is the conductive impairment,need no masking when testing the diseased ear. (3) There are conductive impairments binaural, bone-conduction PTT is normal, and air-conduction PTT is higher than interaural attenuation, we cannt get a true bone-conduction PTT by masking, but can determine the type of hearing loss and estimate the integrity of the sensory-neural system by other audiometry measurements.