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使用听性稳态反应技术需注意的问题
听性稳态反应(auditory steady state responses,ASSR)是近几年发展起来的一种诱发电位测听技术,它采用正弦调幅音或调频调幅音作为刺激声,利用听神经对调制率的锁相反应,在脑电波中以能否检测出与调制率一致的反应波来判断受试者是否听到刺激声.这种方法的刺激声是持续声,所以刺激强度高,高可达1 20 dB№,结果判定是通过电脑中设定的特定程序自动判断,而且刺激声尤其是调幅音的频率特性较好,因此受到不少听力学者的关注.近几年,国内这种方法也逐步在临床推广开来,也可以看到越来越多的相关文献报道.我中心作为国内早开展这项工作的机构,一直关注着这项技术在国内外的进展情况,对于目前这项技术在国内的应用,有几个问题应引起注意.
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骨导听觉稳态反应
听觉稳态反应(auditory steady state responses,ASSR)是由调制声信号的反应相位与刺激信号相位引起的具有稳定关系的听觉诱发电位.近年来关于ASSR的研究报道较多,其中大部分是关于气导ASSR的研究.然而如同其它听力检测方法,气导测试仅能评估听力损失的程度,不能判断听力损失的类型(如鉴别传导性,感音神经性及混合性聋),如气骨导联合应用可弥补这一缺陷.因此随着ASSR广泛应用于临床,骨导ASSR(BC-ASSR)的研究显得有一定的必要性.本文就骨导ASSR近年来的研究进展及临床应用前景综述如下:
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浅谈多频稳态诱发电位的原理和临床应用
在过去的十年里,使用快速和客观电生理听觉测试的需求日渐增强,在新生儿听力筛查方面的应用更是如此.短声和纯音短声脑干诱发电位用于筛查和临床诊断已在全球得到广泛使用.而多频稳态诱发电位作为一种新的测试手段开始得到关注,将给我们提供一种新的测试婴幼儿频率相关听力的快速技术.
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客观评价听觉稳态反应技术在临床中的应用
听觉稳态反应(auditory steady state responses,ASSR),或多频稳态电位(multiple frequency steady state responses,Mf SSR),现又被称为多频听觉稳态反应(multiple frequency auditory steady state response,Mf ASSR)是一种新的电生理测试技术.考虑到与国际研究术语一致的必要,本文将使用"听觉稳态反应"这个词,英文的缩写是ASSR.
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MRI的CBASS序列对颈段椎管蛛网膜下腔和神经根显示的价值与评价
MRI对脊柱及周围组织的显示情况和价值已得到肯定[1],但MRI的稳态平衡扫描(Completely Balance Acquisition in steady state,CBASS)序列对颈部脊椎管的显示情况与CT扫描显示情况的比较研究尚未见类似报道.本文随机抽取行CBASS序列颈部横断扫描样片和行CT颈椎间盘横断扫描样片各30例,以相应层面对照分析,并着重研究C6~7层面的蛛网膜下腔和神经根显示情况.报告如下.
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听觉稳态反应在成人听力诊断中的应用进展
听觉稳态反应(Audio Steady State ResponseASSR)是一种电生理测试技术,是听觉诱发电位的新进展,近几年临床应用逐渐增多,常用于婴幼儿的听力诊断和助听器验配,在成人听力诊断中的应用,尚缺乏充足的经验.
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多频听觉稳态反应研究进展
听觉稳态反应(auditory steady-state response, ASSR),又称多频稳态电位(multi-frequency steady state potential, MFSSP)或多频听觉稳态反应(multiple frequency auditory steady state response, MFASSR),是一种新的电生理测试技术,是由多个频率持续的稳态的声刺激诱发的听觉系统反应[1].1981年Galambos等首先在临床上发展应用ASSR,即40 Hz相关电位.现在,ASSR以其频率特异性好、大声输出高及结果判断客观等优点在国内外得到广泛应用.
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多频稳态反应及其应用
多频稳态反应(multiple steady state responses, MSSR),也称多频稳态电位(multi-frequency steady state potential, MFSSP)、调幅跟随反应(amplitude modulation following response,AMFR),有的也简称为听觉稳态反应(auditory steady state responses,ASSR),是由多个频率持续的或者说是稳态的声音刺激信号刺激产生的反应.初的听觉稳态反应是Galambos[1]等首先记录到的.当时他采用的是30~50 Hz的刺激频率,即40 Hz相关电位.
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小儿多频稳态诱发电位的临床应用
多频稳态诱发电位(multi-frequency steady state evoked potential,MFSSEP)作为一种听力客观测试方法正应用于临床,为了进一步了解MFSSEP的临床应用价值,选取103例同时做MFSSEP和ABR测试的患者资料,再从中筛选出53例既有完整MFSSEP反应阈,又有纯音听阈的资料进行统计分析,报告如下:
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Cellular energy status is often believed to be crucial in the patho physiology of severe acute diseases involving sepsis or trauma such as multiorgan failure, mu ltiorgan dysfunction syndrome, systemic inflammatory response system, etc. Wit h this in mind increased blood lactate, mainly considered only as a marker or t issue hypoxia is a classical tool used to assess the severity of the illness an d to predict the pejorative outcome. However, during the past years the actual r ole of hypoxia in the pathophysiology of such acute diseases with an increased b lood lactate has been questioned.The association between increased blood lactate concentration and poor prognosi s in ICU patients is well documented but it is clearly not a cause-effect relat ionship. It is similar to what occurs in the case of increased blood ketone I n severe insulin deficient state and it would be a major understanding to be lieve that lactate is a toxic compound in acute states. In acute illness, incre ased lactate concentration or lactate metabolism can be due to the combination of various origin in which the role of splanchnic bed is prominent. In the case of strong reduction in oxygen delivery, such as severe shock, it is quite clear that there is a relationship between cellular energy defect and increased lact ate production. But even in these cases a decrease in lactate metabolism (eithe r oxidative or recycling routes) may also be involved. In septic states, the ro le of blood lactate is a matter of controversy and several reports have e mphasiz ed the fact that hyperlactatemia in sepsis was not due to the oxygen d eficit. It has been shown that mild hyperlactatemia in stable septic patients was due to an impaired lactate clearance rather than overproduction. Besides the main conc lusion that any therapeutic attempts to increase oxygen delivery in such situa tion may not be adapted, another point can be raised concerning the meaning of s uch lactate increase. In fact, increased blood lactate concentration in such sta tes might not be a deleterious event but rather an adaptive response, as in th e case of hypoxia.The pathway of lactate metabolism and its regulation has long been known and it s role as carbon shuttle has been extended to all organs and to energy or redox shuttling. Indeed, lactate must be viewed as a key metabolic intermediate betwee n cells or organs for energy metabolism. Erythrocytes, anaerobic cells, produce ATP by the non-oxidative glycolytic pathway with lactate release while liver which produces ATP from β-oxidation, uses this energy to synthesize glucose fr o m lactate. Hence, by recycling the carbons between lactate and glucose, the liv er actually “respire” for the erythrocyte mass. Since almost all cells can be e ither lactate producers or consumers in view of the whole-body energy economy. In the situation of chronic hypoxia, plasma lactate is increased and this is s upposed to be due to an increased peripheral lactate production. An experiment that has been undertaken on liver lactate metabolism with hypothesis that in vivo would lead to an enhanced liver lactate uptake (since recycling gluc ose- lactate was supposed to be increased), surprisingly showed that a very clear inh ibition was located at the phosphoenolpyruvate carboxykinase whose transcription was depressed by hypoxia. Hence, the net result of hypoxia on lactate metaboli sm is an increase in the steady state of lactate of blood lactate concentratio n due to the inhibition of liver lactate metabolism and the question arises of the metabolic meaning of such increase in lactate.The increase in lactate might be viewed as a key metabolic event permitting to modify the cell metabolism according to the new condition of hypoxia. In norm oxic condition the concentration of lactate, release by red blood cells is low and it is mainly recycled via liver gluconeogenesis. In peripheral tissues, su ch as muscle or heart, the main substrate is the glucose which is oxidized to CO2 only a small part being possibly released as lactate. During hypoxia, the co ncentration of lactate is higher, due to the liver inhibition and then in many tissues (muscle) the competition between lactate and glucose as carbohydrate s ource for oxidation might be in favor of lactate. This permits to spare some gl ucose for the privileged tissues such as heart. This has been shown in humans w here chronic hypoxia led to an increase glucose in heart. In acute situation, our recent investigation in cardiac surgery patients usin g an exogenous lactate challenge, whereby one could investigate the dynamic asp ect of lactate metabolism (lactateproduction, lactate clearance) together with other previous similar work (including liver surgery and brain metabolism) showe d that the increased lactate concentration permits an increase of substrate read ily oxidizable even after a transient period of hypoxia or ischemia. Furthermore , by permitting shuttle energy, redox power or carbons from one organ to another , lactate metabolism allows an intra- or interorgan cooperation which in turn l imits the energy failure of one organ by metabolism of another such as the liver for example. Although high lactate is related to poor outcome, this compound I s a “survival kit” rather than a “suicide mode”.
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磁共振3D-CISS序列在儿童梗阻性脑积水中的应用
脑积水(hydrocephalus)是各种原因导致脑脊液产生和吸收不平衡所致的脑室、蛛网膜下腔异常积聚,部分或全部异常扩大,造成儿童神经系统严重损害一种常见病。其根本治疗方法为外科手术,术后随着脑室内积水的减少和脑压的降低,大脑组织可继续正常发育,认知功能得到逐步恢复。因此,术前明确脑脊液循环的梗阻位置,是手术成功的关键。磁共振三维稳态构成干扰序列(three dimensional constructive inference in steady state,3D-CISS)是近年来新开发的磁共振成像应用序列,成功地显示成人的内耳膜迷路、颅脑神经及中脑导水管等细微结构[1-6]。本文就近年来该序列在脑积水的临床研究作一综述。
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bSSFP成像序列在体早期检测脑转移瘤的价值探讨
脑转移瘤(brain metastasis,BM)是成人中枢神经系统常见的恶性肿瘤,其发病率和死亡率在晚期癌症患者中是一个显著因素。BM的早期发现与诊断有利于指导临床治疗措施的选择。目前认为 MR I 增强扫描在发现BM方面具有高的敏感性。但病灶的强化依赖于血脑屏障的破坏,研究表明 BM早期血脑屏障可保持完整,使得MR I增强扫描的敏感性受到限制。平衡稳态自由进动(balanced steady state free precession,bSSFP)序列具有高空间分辨率、高对比度、扫描时间短及无对比剂增强的特点,在实验性脑转移瘤的检测中取得了很高的敏感性。本文对 bSSFP在BM方面的应用价值做一综述。
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磁共振True FISP序列在肝脏疾病影像学评价中的应用
MR T2WI对肝脏局灶性病变的检出和定性诊断起着非常重要的作用[1-2],随着近年来MRI技术的进步,1次屏气即可完成全肝T2WI的图像采集[1-3].真实稳态进动快速成像(true fast imaging with steady precession,True FISP)序列在肝脏疾病的临床诊断及治疗中发挥着越来越重要的作用.True FISP序列成像速度极快,单层采集时间短,对呼吸运动不敏感,即使不能自主屏气的病人也能获得较清晰图像.SIEMENS公司称之为真实稳态进动快速成像True FISP(true fast imaging with steady precession)序列;GE公司称之为快速平衡稳态进动成像FIESTA(fast imaging employing steady state acquisition)序列;PHLIPS公司称之为B FFE(balance fast field echo)技术[4-5].现就MR True FISP的成像原理、成像方法及其在肝脏疾病的诊断和治疗中的研究现况及发展前景予以综述.
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关节软骨双回波稳态序列磁共振成像研究进展
关节软骨的完整性决定着关节的功能状态.大量研究表明关节软骨损伤的患病率较高,而软骨损伤被公认为是不可逆性关节退变过程的一个早期因素[1-4].磁共振成像(magnetic resonance imaging,MRI)具有多方位、多序列、多参数成像及组织分辨率高等优点,目前被公认为关节软骨病损首选佳的无创检查手段[5].早期对关节软骨MRI研究较多的是自旋回波序列T1加权成像(T1 Weighten Imaging ,T1WI)、T2加权成像(T2 Weighten Imaging,T2WI)及少数梯度回波(gradient recall echo,GRE)序列,受当时的MR成像技术条件的限制,图像空间分辨率及信噪比均较低,对于软骨损伤显示的能力相当有限.近些年来,随着MR成像技术的发展,特别是梯度回波序列的开发利用,显示关节软骨的能力大为加强,MRI在关节软骨病变诊断中的重要应用价值已经被广泛认识与接受.各种关节软骨的MRI序列开发成为了许多课题研究的焦点[6-13],而双回波稳态(double echo steady state,DESS) 成像是近期唯一在西门子公司的MR设备上研发的GRE.近年一些研究表明,DESS序列在关节软骨成像中具有重要应用价值[14-22],亦是当今MRI梯度回波序列研究的焦点之一,现综述如下.