盧偉 魯倩 莫玲燕

1 鄭州大學第一附屬醫(yī)院耳科(鄭州 450052); 2 首都醫(yī)科大學附屬北京同仁醫(yī)院,北京市耳鼻咽喉科學研究所,耳鼻咽喉頭頸科學教育部重點實驗室(首都醫(yī)科大學)

3.4 大齡兒童P1N1 這個年齡段包括了4歲到青春期的兒童,目前對于此年齡段的兒童P1N1的研究已經(jīng)相當成熟。成人的P1N1是穩(wěn)定而普遍存在的,而兒童的P1N1的特性尚不明確。P1波幅及潛伏期隨年齡增長而逐漸減小,直到20歲左右達到成人水平[10]。在這個年齡段,N1波分為N1a、N1b(圖3),N1a波只在一部分受試者中觀察到,N1b波在所有受試者中都存在,隨著年齡的增長,N1a波出現(xiàn)的頻率也增長,6～7歲兒童中N1a波出現(xiàn)概率為61%,8～9歲為63%,10～12歲為 69%,13～15歲為100%[10]。N1波的潛伏期及波幅,不同的研究顯示結(jié)果不同[10]：關于潛伏期,有報道在16歲之前,N1波的潛伏期隨著年齡的增加而減小[22],也有報道是在20歲之前[23];關于波幅,有學者認為在15歲之前N1波的波幅隨年齡的增長而增加,也有學者認為潛伏期和波幅與年齡幾乎沒有關系[24]。N1波由三種亞型組成,也有報道認為N1波可能存有其他的成分[3]。目前對N1波研究的重點為N1a與N1b。N1a波最早在6歲的兒童中觀察到,并且其出現(xiàn)的頻率隨著年齡的增加而增加,這種趨勢一直持續(xù)到13歲,但N1a波并不是在所有的兒童中都出現(xiàn),而N1b波幾乎存在于所有兒童中[10]。有學者認為N1a波是成人N1波的前體[10],目前 N1a、N1b與成人N1波之間的關系尚未確定,將來對于達到成人N1波水平前的N1a、N1b變化的研究有重要意義。盡管有報道指出不同的刺激聲產(chǎn)生不同的P1N1波,但在不同刺激下,P1N1各波潛伏期、幅值變化的總趨勢是一致的[10]。隨著年齡的增長,由于神經(jīng)髓鞘不斷發(fā)育以及突觸同步化逐漸完善,P1N1各個成分在不斷的成熟[25]。

圖3 6～12歲兒童的N1a波

4 P1N1的臨床應用和展望

4.1 行為聽閾的評估 P1-N1-P2的刺激聲相對于ABR的短純音而言持續(xù)時間長,且頻率特異性好,對于肢體輕微活動產(chǎn)生的電生理噪聲耐受性強,而且反映的聽覺通路更長,與PTA閾值相關性強,閾值評估效果較好,所以P1-N1-P2閾值能客觀地反映受試兒的實際聽力水平。有研究報道P1-N1-P2閾值與行為聽閾之差在10 dB之內(nèi)[26]。當患兒不能配合主觀行為測聽時,慢皮層P1-N1-N2反應也可以作為一種選擇。但P1-N1-P2易受受試兒精神狀態(tài)及注意力水平的影響,對于不能保持穩(wěn)定清醒狀態(tài)的受試兒,其應用受到限制。

4.2 言語感知的評估 CAEP的發(fā)育受聽覺經(jīng)驗的影響,早期聽覺經(jīng)驗有助于皮層CAEP的發(fā)育。聽覺傳導通路疾病患兒與正常兒童的P1-N1-P2有顯著的差異,尤其是言語功能障礙的兒童其N1波潛伏期明顯延長[27]。在純音或言語聲刺激下,聽神經(jīng)瘤(AN)患兒的 P1、N1波的潛伏期隨聽力損失程度的增加而逐漸延長[28]。AN患兒CAEP各波與他們的言語感知能力有著密切的關聯(lián)：在助聽情況下,CAEP與同齡正常聽力兒童相似的AN患兒,其言語感知能力得分較高;而CAEP潛伏期較同齡正常兒童延長的AN患兒,其言語感知能力很差;CAEP各波缺失的AN患兒,其言語感知能力非常差[28]。由于CAEP與言語感知顯著相關,而言語感知與神經(jīng)元同步化又有著密切聯(lián)系,因此CAEP檢測方法有助于預估神經(jīng)元失同步化的嚴重性。當CAEP存在時,表明有足夠的殘余神經(jīng)元同步化存在,能為編碼言語感知提供所需要的信息,因此CAEP可作為評估言語感知能力的檢測方法[28]。

4.3 聽力障礙兒童助聽后聽力言語的評估 使用助聽器后通常會導致皮層 ERP各成分波形潛伏期縮短,波幅增大[29]。感音神經(jīng)性聾兒助聽后CAEP的改變表明,大部分5～24月齡的極重度聾患兒助聽后對短聲誘發(fā)的CAEP閾值比未助聽時低20 dB[30]。Kurtzberg等[31,32]以4個年齡從7月齡到27月齡、聽力損失從中度到重度的嬰幼兒為受試對象,以言語聲為刺激聲進行測試,發(fā)現(xiàn)助聽后3名患兒有明顯的P1波及其后的寬大負波,并且這些外源性反應只在助聽下才會出現(xiàn),說明助聽后言語識別能力提高。因此,CAEP可以作為助聽效果評估的客觀指標。

4.4 電刺激誘發(fā)的CAEP 關于人工耳蝸植入兒童電刺激誘發(fā)的CAEP的研究在逐步開展,其用于推斷聽覺傳導通路的發(fā)育情況,評估人工耳蝸術后效果。植入人工耳蝸的兒童CAEP只有P1、N2波,而未記錄到N1波,N1波缺失可作為人工耳蝸植入兒童CAEP的明顯標志[33,34]。電刺激誘發(fā)的CAEP有一寬大的正波及其前的負波[35],Sharma等[36]認為這一正波為P1波,其潛伏期隨著年齡的增長和人工耳蝸使用年限的增加而減小(圖4),P1潛伏期延長與否表明了聽覺傳導系統(tǒng)的發(fā)育程度,同時,短潛伏期負波的出現(xiàn)(此負波可能波幅較小或波幅寬大),表明皮層神經(jīng)沖動發(fā)放異常。不規(guī)則的皮層反應可能由在聽力損失期間皮層的異常變化所引起,也可能是由于使用人工耳蝸期間皮層的異常變化所造成,這些變化可能反映了除簡單察覺反應之外的其他皮層活動,而這些皮層活動是獲得言語感知的必需成分[35]。Sharma等[36]通過對不同年齡階段的植入人工耳蝸的兒童與同齡正常兒童P1潛伏期的比較,發(fā)現(xiàn)3.5歲前植入人工耳蝸者,其P1潛伏期值與同齡正常兒童的P1潛伏期值類似;3.6歲到6.5歲植入人工耳蝸者,大部分患兒P1潛伏期與同齡正常兒童不同;7歲之后植入耳蝸者,與同齡兒童相比,P1潛伏期值顯著增加。因此推斷先天性聾患兒的聽覺傳導通路并沒有完全退化或者說仍具有很大的可塑性[36],3.5歲前是先天性聾患兒進行耳蝸植入的最佳時期[37,38]。

圖4 P1潛伏期隨人工耳蝸使用時間的變化情況[36]

4.5 展望 P1N1的波幅和潛伏期能夠反映聽覺通路的發(fā)育程度。CAEP技術在行為閾值及聽覺認知功能的評估方面有重要的應用價值,在不久的將來,它將會廣泛運用到臨床聽力學中。

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