Shi Y, Martin W H
Garfield Auditory Research Laboratory, Temple University Medical School, Philadelphia, PA 19140, USA.
J Basic Clin Physiol Pharmacol. 1997;8(3):141-55. doi: 10.1515/jbcpp.1997.8.3.141.
Auditory brainstem responses (ABR) and distortion product otoacoustic emissions (DPOAE) have been applied to the evaluation of peripheral auditory function. To date, no comparison of their relative sensitivities to aminoglycoside toxicity has been reported. The purpose of this study was to compare click evoked ABR testing and 2f1-f2 DPOAEs as detectors of cochlear damage induced by gentamicin treatment in guinea-pigs. ABR thresholds to click stimuli were recorded. DPOAE amplitude input/output functions were recorded using three different primary tone level conditions. In one condition, L1 was changed relative to a fixed L2. In the next condition, L2 was changed relative to a fixed L1. In the third condition, L1 and L2 were both changed while maintaining a consistent L1-L2 difference. Baseline L1-L2 differences were determined by adjusting L2 to produce the maximum DPOAE amplitude in each ear of each subject. Guinea-pigs were treated for a four week period with intramuscular injections of gentamicin. ABRs and DPOAEs were monitored and compared to baseline recordings or untreated control groups. DPOAE testing detected cochlear damage earlier than ABR testing. Changes in DPOAE input/output functions were noted after two weeks of treatment while changes in ABR threshold were not identified until after three weeks of treatment. The sensitivity of the DPOAE testing was related to the stimulus conditions utilized. L1-L2 differences were determined in the control group and for the initial test session by fixing L1 at 75 dB SPL and lowering L2 until the maximum DPOAE amplitude was obtained for each ear. All subsequent testing was begun using the optimal L1-L2 difference for each ear. The stimulus condition in which only L1 was changed and L2 was fixed resulted in the least sensitive DPOAE indicator of cochlear damage. The condition in which both L1 and L2 were changed, but the L1-L2 difference remained constant, resulted in the most sensitive indicator of damage. The onset and degree of cochlear damage secondary to gentamicin treatment was subject dependent. This study demonstrates that 2f1-f2 DPOAE testing is preferable to click evoked ABR testing for early detection of gentamicin toxicity of the cochlea. It also indicates that DPOAE stimulus parameters must be considered when developing test protocols. Specifically, recording the DPOAE amplitude input/output function while maintaining an effective L1-L2 difference is preferable to changing either L1 or L2 individually.
听性脑干反应（ABR）和畸变产物耳声发射（DPOAE）已被应用于外周听觉功能的评估。迄今为止，尚未有关于它们对氨基糖苷类毒性相对敏感性比较的报道。本研究的目的是比较短声诱发ABR测试和2f1-f2 DPOAE作为豚鼠庆大霉素治疗所致耳蜗损伤检测方法的效果。记录短声刺激的ABR阈值。使用三种不同的初始音水平条件记录DPOAE幅度输入/输出函数。在一种条件下，L1相对于固定的L2进行改变。在接下来的条件下，L2相对于固定的L1进行改变。在第三种条件下，L1和L2同时改变，同时保持L1-L2差值恒定。通过调整L2以在每个受试者每只耳朵中产生最大DPOAE幅度来确定基线L1-L2差值。豚鼠通过肌肉注射庆大霉素进行为期四周的治疗。监测ABR和DPOAE，并与基线记录或未治疗的对照组进行比较。DPOAE测试比ABR测试更早地检测到耳蜗损伤。治疗两周后就注意到DPOAE输入/输出函数的变化，而直到治疗三周后才发现ABR阈值的变化。DPOAE测试的敏感性与所采用的刺激条件有关。在对照组和初始测试阶段，通过将L1固定在75 dB SPL并降低L2直到每只耳朵获得最大DPOAE幅度来确定L1-L2差值。所有后续测试均从使用每只耳朵的最佳L1-L2差值开始。仅改变L1而L2固定的刺激条件导致DPOAE对耳蜗损伤的指示最不敏感。L1和L2都改变但L1-L2差值保持恒定的条件导致对损伤最敏感的指示。庆大霉素治疗继发的耳蜗损伤的发生和程度因个体而异。本研究表明，对于早期检测庆大霉素对耳蜗的毒性，2f1-f2 DPOAE测试优于短声诱发ABR测试。它还表明，在制定测试方案时必须考虑DPOAE刺激参数。具体而言，在保持有效的L1-L2差值的同时记录DPOAE幅度输入/输出函数比单独改变L1或L2更可取。
