儿童皮层诱发电位中P1N1的增龄性变化及临床应用*(2)

卢伟 鲁倩 莫玲燕

1 郑州大学第一附属医院耳科(郑州 450052); 2 首都医科大学附属北京同仁医院,北京市耳鼻咽喉科学研究所,耳鼻咽喉头颈科学教育部重点实验室(首都医科大学)

3.4 大龄儿童P1N1 这个年龄段包括了4岁到青春期的儿童,目前对于此年龄段的儿童P1N1的研究已经相当成熟。成人的P1N1是稳定而普遍存在的,而儿童的P1N1的特性尚不明确。P1波幅及潜伏期随年龄增长而逐渐减小,直到20岁左右达到成人水平[10]。在这个年龄段,N1波分为N1a、N1b(图3),N1a波只在一部分受试者中观察到,N1b波在所有受试者中都存在,随着年龄的增长,N1a波出现的频率也增长,6～7岁儿童中N1a波出现概率为61%,8～9岁为63%,10～12岁为 69%,13～15岁为100%[10]。N1波的潜伏期及波幅,不同的研究显示结果不同[10]：关于潜伏期,有报道在16岁之前,N1波的潜伏期随着年龄的增加而减小[22],也有报道是在20岁之前[23];关于波幅,有学者认为在15岁之前N1波的波幅随年龄的增长而增加,也有学者认为潜伏期和波幅与年龄几乎没有关系[24]。N1波由三种亚型组成,也有报道认为N1波可能存有其他的成分[3]。目前对N1波研究的重点为N1a与N1b。N1a波最早在6岁的儿童中观察到,并且其出现的频率随着年龄的增加而增加,这种趋势一直持续到13岁,但N1a波并不是在所有的儿童中都出现,而N1b波几乎存在于所有儿童中[10]。有学者认为N1a波是成人N1波的前体[10],目前 N1a、N1b与成人N1波之间的关系尚未确定,将来对于达到成人N1波水平前的N1a、N1b变化的研究有重要意义。尽管有报道指出不同的刺激声产生不同的P1N1波,但在不同刺激下,P1N1各波潜伏期、幅值变化的总趋势是一致的[10]。随着年龄的增长,由于神经髓鞘不断发育以及突触同步化逐渐完善,P1N1各个成分在不断的成熟[25]。

图3 6～12岁儿童的N1a波

4 P1N1的临床应用和展望

4.1 行为听阈的评估 P1-N1-P2的刺激声相对于ABR的短纯音而言持续时间长,且频率特异性好,对于肢体轻微活动产生的电生理噪声耐受性强,而且反映的听觉通路更长,与PTA阈值相关性强,阈值评估效果较好,所以P1-N1-P2阈值能客观地反映受试儿的实际听力水平。有研究报道P1-N1-P2阈值与行为听阈之差在10 dB之内[26]。当患儿不能配合主观行为测听时,慢皮层P1-N1-N2反应也可以作为一种选择。但P1-N1-P2易受受试儿精神状态及注意力水平的影响,对于不能保持稳定清醒状态的受试儿,其应用受到限制。

4.2 言语感知的评估 CAEP的发育受听觉经验的影响,早期听觉经验有助于皮层CAEP的发育。听觉传导通路疾病患儿与正常儿童的P1-N1-P2有显著的差异,尤其是言语功能障碍的儿童其N1波潜伏期明显延长[27]。在纯音或言语声刺激下,听神经瘤(AN)患儿的 P1、N1波的潜伏期随听力损失程度的增加而逐渐延长[28]。AN患儿CAEP各波与他们的言语感知能力有着密切的关联：在助听情况下,CAEP与同龄正常听力儿童相似的AN患儿,其言语感知能力得分较高;而CAEP潜伏期较同龄正常儿童延长的AN患儿,其言语感知能力很差;CAEP各波缺失的AN患儿,其言语感知能力非常差[28]。由于CAEP与言语感知显著相关,而言语感知与神经元同步化又有着密切联系,因此CAEP检测方法有助于预估神经元失同步化的严重性。当CAEP存在时,表明有足够的残余神经元同步化存在,能为编码言语感知提供所需要的信息,因此CAEP可作为评估言语感知能力的检测方法[28]。

4.3 听力障碍儿童助听后听力言语的评估 使用助听器后通常会导致皮层 ERP各成分波形潜伏期缩短,波幅增大[29]。感音神经性聋儿助听后CAEP的改变表明,大部分5～24月龄的极重度聋患儿助听后对短声诱发的CAEP阈值比未助听时低20 dB[30]。Kurtzberg等[31,32]以4个年龄从7月龄到27月龄、听力损失从中度到重度的婴幼儿为受试对象,以言语声为刺激声进行测试,发现助听后3名患儿有明显的P1波及其后的宽大负波,并且这些外源性反应只在助听下才会出现,说明助听后言语识别能力提高。因此,CAEP可以作为助听效果评估的客观指标。

4.4 电刺激诱发的CAEP 关于人工耳蜗植入儿童电刺激诱发的CAEP的研究在逐步开展,其用于推断听觉传导通路的发育情况,评估人工耳蜗术后效果。植入人工耳蜗的儿童CAEP只有P1、N2波,而未记录到N1波,N1波缺失可作为人工耳蜗植入儿童CAEP的明显标志[33,34]。电刺激诱发的CAEP有一宽大的正波及其前的负波[35],Sharma等[36]认为这一正波为P1波,其潜伏期随着年龄的增长和人工耳蜗使用年限的增加而减小(图4),P1潜伏期延长与否表明了听觉传导系统的发育程度,同时,短潜伏期负波的出现(此负波可能波幅较小或波幅宽大),表明皮层神经冲动发放异常。不规则的皮层反应可能由在听力损失期间皮层的异常变化所引起,也可能是由于使用人工耳蜗期间皮层的异常变化所造成,这些变化可能反映了除简单察觉反应之外的其他皮层活动,而这些皮层活动是获得言语感知的必需成分[35]。Sharma等[36]通过对不同年龄阶段的植入人工耳蜗的儿童与同龄正常儿童P1潜伏期的比较,发现3.5岁前植入人工耳蜗者,其P1潜伏期值与同龄正常儿童的P1潜伏期值类似;3.6岁到6.5岁植入人工耳蜗者,大部分患儿P1潜伏期与同龄正常儿童不同;7岁之后植入耳蜗者,与同龄儿童相比,P1潜伏期值显著增加。因此推断先天性聋患儿的听觉传导通路并没有完全退化或者说仍具有很大的可塑性[36],3.5岁前是先天性聋患儿进行耳蜗植入的最佳时期[37,38]。

图4 P1潜伏期随人工耳蜗使用时间的变化情况[36]

4.5 展望 P1N1的波幅和潜伏期能够反映听觉通路的发育程度。CAEP技术在行为阈值及听觉认知功能的评估方面有重要的应用价值,在不久的将来,它将会广泛运用到临床听力学中。

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