聽覺誘發電位在評估嬰幼兒聽力損失與成人耳鳴之運用

Abstract

論述重點: 客觀的音頻誘發聽性腦幹反應可以準確評估主觀上行為觀察聽力檢查所得語言頻率上的聽力好壞。本研究的第一部份在利用客觀的音頻誘發聽性腦幹反應去量測已知聽力正常的嬰幼兒，先建立起各語言頻率下的客觀正常聽閾數值，作為後續研究中比較客觀與主觀聽力檢查的正常參考值。接著在第二部份的研究中，我們進一步以較大規模的音頻誘發聽性腦幹反應與行為觀察聽力檢查資料進行統計分析。想找出客觀與主觀聽力檢查的相關程度，並了解成長年齡與不同的聽力損失對於上述相關所造成的影響。為了更進一步探討臨床上病人主觀的聽覺症狀耳鳴是否也可以經由客觀的聽力檢查加以量測，在第三部份的研究中，我們採用潛時較長的大腦皮質音頻誘發反應來探討耳鳴病人的聽覺病態，嚐試可否利用客觀的聽覺機能檢測表現出主觀的耳鳴特質，並運用作臨床上的診斷評估工具。 研究方法: 在第一部分的研究中，共有94位年齡介於3個月到3年之間的嬰幼兒接受了一系列的聽力檢查，包括音頻誘發聽性腦幹反應。利用統計分析其中4個頻率下的各項變數之間的關係，並建立正常參考值。接下來我們將實驗主體的數目擴充到1281位年齡介於3個月到3年之間的嬰幼兒，同樣接受一系列的聽力檢查，並包括音頻誘發聽性腦幹反應及聲場聽力檢查。利用統計分析其中4個語言頻率下兩種方法所量測的聽閾與各項變數之間的關係，並探討成長年齡與不同的聽力損失狀況下，上述兩種檢查結果的一致性與相關程度如何受到影響。在第三部份的研究中，我們在9位耳鳴病患與9位正常人進行大腦皮質音頻誘發反應的測量，分別記錄五種刺激強度(50, 56, 62, 68 and 74 dB nHL)及4個語言頻率下N1-P2在36個頭皮電極的波型變化。利用統計分析其中位電極記錄到的N1-P2隨刺激強度變化的情形。 結果: 第一部分的研究結果顯示嬰幼兒在一般語言頻率(500, 1000, 2000, and 4000 Hz)下，以音頻誘發聽性腦幹反應推測的聽閾大概介在10到20 分貝之間。其中性別、左右側及成長年齡並不影響測量的結果。第二部分的研究結果顯示嬰幼兒在一般語言頻率(500, 1000, 2000, and 4000 Hz)下，接受音頻誘發聽性腦幹反應及聲場聽力檢查推估的聽力狀態有明顯的相關(Ps＜0.001)，且該相關不受成長年齡與不同的聽力損失所影響。不過在聽力損失極為輕微的狀態下，相關強度稍受影響。其中，20分貝以下的聽力損失狀態下，在3個語言頻率下(1000, 2000 and 4000 Hz)未能保持相關。第三部分的研究結果顯示，異常的大腦皮質音頻誘發反應隨刺激強度變化的情形，在4個語言頻率下整體出現不同於正常族群。然而這樣的結果並未重現於任何單一的頻率下。 結論: 根據以往的文獻報告與本實驗的結果，我們建議將嬰幼兒的音頻誘發聽性腦幹反應推測的正常聽閾於500, 1000 Hz處的下限訂在30分貝，2000, 4000 Hz處的下限訂在25分貝。測量的過程中，考量成長年齡與不同的聽力損失所可能造成的些微影響，先進行音頻誘發聽性腦幹反應推估的聽力狀態對最終行為觀察聽力檢查所得的診察結果極有助益。另外，利用客觀的聽覺機能檢測表現出主觀的耳鳴特質在大腦皮質音頻誘發反應的測量中獲得初步的証實。該表現在聽力正常的耳鳴病患未出現邊緣頻率的特性，指出現在有聽力損失的耳鳴病患上。後續研究將有助於進一步將客觀的聽覺機能檢查運用於臨床上診斷主觀聽覺病態的評估工具。

Background/Purpose: Objective measurement by tone burst evoked auditory brainstem response provides relatively accurate estimates of the behavioral auditory thresholds at speech frequencies. The first part of this study reports the preliminary data of tone burst auditory brainstem response measurements in infants and very young children. As an excellent agreement and correlation between objective evoked-potential and subjective behavioral thresholds have been demonstrated by previous studies, the second part of this study investigates the effects of different age and degree of hearing loss on the above agreement and correlation. Comparison was made between objective tone burst auditory brainstem responses and subjective sound field audiometry. To further compare the differences between objective and subjective measures, the third part of this study applied another evoked potentials test to investigate if the subjective tinnitus demonstrates increased intensity dependence objectively at the selected frequencies. Methods: Of the part one study, 94 infants and very young children from 3 months to 3 years of age underwent tone burst auditory brainstem response measurements at selected four frequencies. Statistical methods were applied to study the relationship among recorded variables. In the part two, 1281 infants and very young children aged from 3 months to 3 years underwent diagnostic audiometry including sound field audiometry and tone burst auditory brainstem response measurements. Statistical analyses were applied to investigate the effects of age and hearing loss on the agreement and correlation between two measured thresholds. In the part three, we applied auditory cortical evoked potential test to investigate 9 tinnitus patients and 9 age- and sex-matched healthy subjects without tinnitus. Auditory cortical evoked potentials (N1-P2) were elicited from stimuli at four frequencies (4000, 2000, 1000 and 500 Hz) with five intensities (50, 56, 62, 68 and 74 dB nHL). Intensity dependences by latency of N1 and amplitude of N1-P2 were surveyed at midline electrodes. Results: The results of part one indicate that the averaged tone burst auditory brainstem response thresholds of the infants and young children with normal hearing in Taiwan are typically 10 to 20 dB nHL at 500, 1000, 2000, and 4000 Hz. There is no statistically difference for the thresholds regarding gender, laterality, and age distribution in this study. In part two, significant correlations (Ps＜0.001) were seen between two measured thresholds across groups of different ages and different degree of hearing loss more than 20 dB HL. However, the correlation strength deteriorated along with decreased degree of hearing loss. Correlations for hearing thresholds less than 20 dB HL were not significant at 1000, 2000 and 4000 Hz. In part three, significant differences existed in the intensity dependence of amplitude N1-P2 to the pooled frequencies at Fz and Cz position. These differences suggested that tinnitus patients tended to respond less to increased sound intensity and were inclined to weaker intensity dependence. Conclusion: Based on the published research and our study, we suggest setting the normal criterion levels for the infants and young children in Taiwan of the tone burst auditory brainstem response to air-conducted tones as 30 dB nHL for 500 and 1000 Hz, and 25 dB nHL for 2000 and 4000 Hz. From part two, properly obtained and interpreted with respect to the effects of age and degree of hearing loss, the evoked potentials test provide the very informative hearing threshold reference to perfect the behavioral audiometric evaluation for the infants and very young children with hearing loss. From part three, objectively increased intensity dependence of N1-P2 component at selected frequency can not be demonstrated in tinnitus patients with normal hearing. Restated, the edge frequency phenomenon fails to present in tinnitus patients with normal hearing, a different characteristic from tinnitus patients with hearing loss.