听性稳态反应应用于婴幼儿听力评估的现状

刺激速率为70～110 Hz的听性稳态反应(auditory steady-state response, ASSR)(亦称为80 Hz)最近倍受听力学工作者特别是小儿听力学工作者的关注,设备制造商也正在推销其产品.本文回顾了ASSR的技术、应用基础,并总结了其应用于婴幼儿听力评估的现状.文中斜体字为基本原则.详细的ASSR方法学、正常值以及一些ASSR研究结果请参阅Picton(2003)的综述.ASSR并不是一个新发现的听觉反应,1960年Geisler就从人类头颅上记录到了该反应;以后研究者又记录到了短声、正弦调制波以及方波调制波所诱发的反应.Galambos等在1981年发表的有关40 Hz事件相关电位将ASSR引入听力领域.不同刺激速率的ASSR的产生部位是不同的,40 Hz的ASSR产生于皮层和脑干,而80 Hz的ASSR主要来源于脑干,而且很有可能它就是ABR的波Ⅴ,只是与ABR的刺激和记录方法不同而已.ASSR的重要特征之一就是在频域内分析的方法,通过计算位相相关性或刺激速率值处的信噪比,再根据统计学分析来判定反应的引出与否,这种客观性使ASSR显著优于ABR.ASSR的刺激信号最早是象ABR一样的短纯音信号,以后主要用调幅调制声,有时也加入10%～20%的调频调制,目前大多数设备都采用这一信号,最近一种新ASSR设备的缺省设置是5～8 ms的短音.ASSR的另一个重要特征是能够同时记录多个刺激声信号所产生的反应,这种多频刺激的方法能够同时记录双耳八个频率(每耳四个频率)的反应.研究证明只要各个信号的频率相距一个倍频程以上,强度在75 dB SPL以下,多个刺激声之间的干扰就很小或没有.不对称型的听力图、不同频率所产生的反应幅度的不同以及多频刺激方式所导致的各个频率反应幅度整体的下降延长了这种方法的测试时间,使其不如理想中的那么省时,但仍比单一刺激方式快2～3倍.80 Hz ASSR通常采用的是正弦调幅调制纯音,因为其特有的频率特异性而被认为是优于短纯音ABR的一个方面,但是声信号的频率特异性只是其中的一方面,还应考虑到耳蜗基底膜的部位特异性以及神经反应的特异性.研究证明ASSR的频率特异性与短纯音ABR是非常接近的.ASSR技术以飞快的速度发展,十年前还没有商用的设备,五年前只有两家,而目前至少有六种不同的设备.随着设备的增加,各个设备之间标准化的问题突显出来.有些设备有很浑厚的研究背景,而有些则没有,使用者应该根据设备的性能及临床资料而加以选择.关于80 Hz ASSR与行为听力测试相关性的研究很多,多为感音神经性聋成人或较大儿童,结果表明至少在该人群中ASSR的阈值能够很好地预测行为听力阈值.许多ABR与ASSR的比较研究声称ASSR比ABR能够更好地评估残余听力,也就是当受试者听力损失很重、ABR不能引出时,仍能够引出ASSR.尽管这一现象客观存在,但是还有一些其他需要考虑的影响因素,如:①所比较的信号在某一特定频率上的能量是不相等的,众所周知短声的能量分布频率范围很宽,其最大输出强度较ASSR信号小;②ASSR在高强度会有伪迹或非听性反应;③ASSR的长时强声刺激会导致耳蜗损害.因此需慎重对待这一问题.目前还没有关于传导性聋或混合性聋气导ASSR的研究,模拟传导性聋的研究表明气导ASSR阈值远高于行为听阈,而且ASSR骨气导差过大.骨导ASSR的研究显示听力正常婴幼儿各个频率的ASSR的阈值与成人显著不同.正常听力婴幼儿的短纯音ABR阈值以及诊断标准已经确立,而ASSR在这一方面的研究则显得不足,而且不同研究所采用的刺激(单频与多频)及记录(不同信噪比、噪声标准以及记录时间)方法不同,使这一形势更加恶化.综合不同调幅调制纯音ASSR的研究结果,正常听力婴幼儿在500、1 000、2 000及4 000 Hz的平均阈值分别为41、43、35和32 dB HL,如果转换为dB SPL则与短纯音ABR非常相似.如果以均值的90%～95%为可信区间,取二倍标准差,则诊断标准在500 Hz为60 dB HL,1 000、2 000及4 000 Hz为50 dB HL.关于感音神经性聋儿童ASSR的研究有很多,这种研究比较理想的方法应该将婴幼儿的ASSR阈值与行为听阈或短纯音ABR阈值相比较.遗憾的是多数研究都是短声ABR与ASSR的比较.总结以上工作发现,首先样本数量还很少,其次多数有方法学的缺陷,加之不同研究所采用的刺激和记录方法不同,临床资料就更加减少.最后还没有不同类型听力损失的婴幼儿ASSR的研究.总而言之,尽管ASSR在婴幼儿听力评估方面很有前途,但目前单独以此作为听力诊断的电生理方法还为时过早,还必须结合短纯音ABR,因为只有短纯音ABR才具有充足的基础、临床研究和明确的诊断标准,因而也是目前婴幼儿听力诊断电生理方法的金标准.根据上述回顾,ASSR在婴幼儿听力诊断的现状总结如下:①新的刺激及记录方法通常都没有经过同行审阅的临床科研为依据,特别是缺乏听力障碍婴幼儿的数据;②不同设备采用不同的刺激和记录方法,且缺少专业人员的评估;③不同的方法或设备层出不穷,缺乏标准化;④刺激声信号的校准问题以及ASSR与行为听力之间的关系问题还没有解决,各种设备采用不同的刺激和记录方法更加恶化了这一状况;⑤极重度聋者的ABR和ASSR的关系还有待于进一步研究;⑥听力损失儿童的ASSR与行为听力测试的关系的研究还很少,而且现有的大多数研究没有能够将ASSR与听力诊断的金标准--行为听力和/或短纯音ABR进行比较;⑦六个月以下婴幼儿的ASSR 研究还很少;⑧传导性聋或混合性聋成人和婴幼儿的研究还很少;⑨成人的骨导ASSR研究很少,还没有婴幼儿骨导ASSR的研究报道,也没有病理状态下成人或婴幼儿的骨导ASSR研究(极重度聋除外).如果上述问题得不到解决,ASSR技术就不能称为成熟.因为对于一个结果,无法准确地判定该阈值是正常还是升高.短纯音ABR的研究虽然尚需完善,但它已有非常多的研究背景和临床数据,能够提供气导和骨导听阈,是当前婴幼儿(特别是6个月以下儿童)听阈确定的首选方法.因此目前ASSR还需与短纯音ABR或行为听力测试结合使用. 80 Hz ASSR除了用于阈值的评估外,也可以用于阈上功能的评估,如单词识别或助听器效果的预估.结果 表明在正常或异常听力成人以言语调制声为信号,其识别阈与ASSR有显著相关性,它反映了较低水平的听觉处理能力.     

Timing of supplementation of selenium and isoflavones determines prostate cancer risk factor reduction in rats

Drug-drug interactions have become an important issue in health care. It is now realized that many drug-drug interactions can be explained by alterations in the metabolic enzymes that are present in the liver and other extra-hepatic tissues. Many of the major pharmacokinetic interactions between drugs are due to hepatic cytochrome P450 (P450 or CYP) enzymes being affected by previous administration of other drugs. After coadministration, some drugs act as potent enzyme inducers, whereas others are inhibitors. However, reports of enzyme inhibition are very much more common. Understanding these mechanisms of enzyme inhibition or induction is extremely important in order to give appropriate multiple-drug therapies. In future, it may help to identify individuals at greatest risk of drug interactions and adverse events.     

Psychological response to growth hormone treatment in short normal children.

This study provides a controlled assessment of the psychological (and physical) effects of growth hormone treatment. Fifteen short ''normal'' children (height SD score < -2) have been treated with growth hormone since the age of 7/8 years. They, together with untreated short controls and average controls (10th-90th centiles), were assessed at recruitment, after three years, and after five years. Only the treated group showed a significant height increase (SD score -2.44 to -1.21 over five years). No significant differences were found at recruitment, three years, or five years in IQ, attainment, behaviour, or self esteem. Also at five years, there were no significant differences in locus of control, self perception, or parental perceptions of competence. Both short groups displayed less satisfaction with their height than the controls (p < 0.01), though all groups were optimistic of being tall adults. The treated children were no more unrealistic over final height than the untreated children. To date, no psychological benefits of treatment have been demonstrated; but nor have there been any discernible ill effects for either the treated or the untreated children.     

Shwachman-Diamond syndrome: early bone marrow transplantation in a high risk patient and new clues to pathogenesis

Shwachman-Diamond syndrome (SDS) is an autosomal recessive disorder characterised by exocrine pancreas insufficiency, metaphyseal dysostosis and bone marrow dysfunction. Recurrent severe bacterial infections and susceptibility to leukaemia are the major causes of morbidity and mortality occurring preferentially in patients with pancytopenia and features of myelodysplasia. Here we report a patient with SDS leading to recurrent bacterial infections and a deteriorating condition since early infancy. Extensive investigations disclosed severe pancytopenia, myelodysplasia and a clonal cytogenetic abnormality, inv(14)(q11q32), as risk factors of leukaemic transformation. He therefore underwent allogeneic geno-identical bone marrow transplantation which resulted in correction of all haematological and immunological abnormalities within an 18-month follow up period. Conclusion Bone marrow transplantation may be considered early as a valuable treatment option especially in high risk Schwachman-Diamond syndrome patients anticipating malignant transformation, life-threatening severe infections or further organ damage. Received: 19 February 1999 / Accepted: 22 June 1999     

Rehabilitation-specific communication skills training: improving the physician-patient relationship.

OBJECTIVE: Evaluate the effectiveness of a rehabilitation-specific communication skills training program for physicians. DESIGN: Three groups of rehabilitation patients were interviewed 3 mo after discharge, one group before and two groups after implementation of a communication skills training program. The setting was a free-standing rehabilitation hospital with a residency training program. A total of 245 patients who had been discharged from the rehabilitation hospital participated in the study. A communication skills training program that was designed specifically for physicians and patients in the rehabilitation setting was used as an intervention. Patients' perceptions of the extent to which physicians accomplished 18 communication tasks highlighted by the training program were gauged in a structured telephone interview. RESULTS: Participants interviewed after the training program was implemented more strongly agreed that their physicians accomplished the communication tasks assessed than did patients interviewed before the training program began. On 14 of 18 items, the differences were statistically significant (P < 0.05). CONCLUSION: Specialty-specific communication training can improve physician communication skills.