兒童皮層誘發(fā)電位中P1N1的增齡性變化及臨床應(yīng)用*(2)

盧偉 魯倩 莫玲燕

1 鄭州大學(xué)第一附屬醫(yī)院耳科(鄭州 450052); 2 首都醫(yī)科大學(xué)附屬北京同仁醫(yī)院,北京市耳鼻咽喉科學(xué)研究所,耳鼻咽喉頭頸科學(xué)教育部重點(diǎn)實(shí)驗(yàn)室(首都醫(yī)科大學(xué))

3.4 大齡兒童P1N1 這個(gè)年齡段包括了4歲到青春期的兒童,目前對(duì)于此年齡段的兒童P1N1的研究已經(jīng)相當(dāng)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(zhǎng)而逐漸減小,直到20歲左右達(dá)到成人水平[10]。在這個(gè)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(zhǎng),N1a波出現(xiàn)的頻率也增長(zhǎng),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(guān)于潛伏期,有報(bào)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(bào)道是在20歲之前[23];關(guān)于波幅,有學(xué)者認(rèn)為在15歲之前N1波的波幅隨年齡的增長(zhǎng)而增加,也有學(xué)者認(rèn)為潛伏期和波幅與年齡幾乎沒有關(guān)系[24]。N1波由三種亞型組成,也有報(bào)道認(rèn)為N1波可能存有其他的成分[3]。目前對(duì)N1波研究的重點(diǎn)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(shì)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(xué)者認(rèn)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(guān)系尚未確定,將來對(duì)于達(dá)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(bào)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(shì)是一致的[10]。隨著年齡的增長(zhǎng),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(gè)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(yīng)用和展望

4.1 行為聽閾的評(píng)估 P1-N1-P2的刺激聲相對(duì)于ABR的短純音而言持續(xù)時(shí)間長(zhǎng),且頻率特異性好,對(duì)于肢體輕微活動(dòng)產(chǎn)生的電生理噪聲耐受性強(qiáng),而且反映的聽覺通路更長(zhǎng),與PTA閾值相關(guān)性強(qiáng),閾值評(píng)估效果較好,所以P1-N1-P2閾值能客觀地反映受試兒的實(shí)際聽力水平。有研究報(bào)道P1-N1-P2閾值與行為聽閾之差在10 dB之內(nèi)[26]。當(dāng)患兒不能配合主觀行為測(cè)聽時(shí),慢皮層P1-N1-N2反應(yīng)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(duì)于不能保持穩(wěn)定清醒狀態(tài)的受試兒,其應(yīng)用受到限制。

4.2 言語感知的評(píng)估 CAEP的發(fā)育受聽覺經(jīng)驗(yàn)的影響,早期聽覺經(jīng)驗(yàn)有助于皮層CAEP的發(fā)育。聽覺傳導(dǎo)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(zhǎng)[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(zhǎng)[28]。AN患兒CAEP各波與他們的言語感知能力有著密切的關(guān)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(zhǎng)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(guān),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(cè)方法有助于預(yù)估神經(jīng)元失同步化的嚴(yán)重性。當(dāng)CAEP存在時(shí),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(píng)估言語感知能力的檢測(cè)方法[28]。

4.3 聽力障礙兒童助聽后聽力言語的評(píng)估 使用助聽器后通常會(huì)導(dǎo)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(duì)短聲誘發(fā)的CAEP閾值比未助聽時(shí)低20 dB[30]。Kurtzberg等[31,32]以4個(gè)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(duì)象,以言語聲為刺激聲進(jìn)行測(cè)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(fù)波,并且這些外源性反應(yīng)只在助聽下才會(huì)出現(xiàn),說明助聽后言語識(shí)別能力提高。因此,CAEP可以作為助聽效果評(píng)估的客觀指標(biāo)。

4.4 電刺激誘發(fā)的CAEP 關(guān)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(dǎo)通路的發(fā)育情況,評(píng)估人工耳蝸術(shù)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(biāo)志[33,34]。電刺激誘發(fā)的CAEP有一寬大的正波及其前的負(fù)波[35],Sharma等[36]認(rèn)為這一正波為P1波,其潛伏期隨著年齡的增長(zhǎng)和人工耳蝸使用年限的增加而減小(圖4),P1潛伏期延長(zhǎng)與否表明了聽覺傳導(dǎo)系統(tǒng)的發(fā)育程度,同時(shí),短潛伏期負(fù)波的出現(xiàn)(此負(fù)波可能波幅較小或波幅寬大),表明皮層神經(jīng)沖動(dòng)發(fā)放異常。不規(guī)則的皮層反應(yīng)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(jiǎn)單察覺反應(yīng)之外的其他皮層活動(dòng),而這些皮層活動(dòng)是獲得言語感知的必需成分[35]。Sharma等[36]通過對(duì)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(dǎo)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(jìn)行耳蝸植入的最佳時(shí)期[37,38]。

圖4 P1潛伏期隨人工耳蝸使用時(shí)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(shù)在行為閾值及聽覺認(rèn)知功能的評(píng)估方面有重要的應(yīng)用價(jià)值,在不久的將來,它將會(huì)廣泛運(yùn)用到臨床聽力學(xué)中。

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