Introdução: A captação e o estudo de respostas cerebrais evocadas por um estímulo sonoro vem permitindo a investigação objetiva do processamento da informação auditiva e uma melhor compreensão da via auditiva central. A utilidade deste método diagnóstico tem sido cada vez mais valorizada pelos audiologistas, no entanto sua aplicação clínica corrente requer a realização de uma quantidade mais expressiva de estudos, especialmente na literatura nacional, para um conhecimento mais profundo deste método, sobretudo quanto a normatizações, critérios de identificação das ondas e interferências de variáveis como idade, sexo e parâmetros utilizados na aquisição. Os Potenciais Evocados Auditivos de Média Latência são compostos por uma seqüência de ondas com latências em torno de 10 a 80ms, com origem neurogênica múltipla (projeções tálamo-corticais e córtex auditivo, colículo inferior e formação reticular em menor escala). O presente estudo tem como objetivo pesquisar os componentes dos PEAMLs, numa população de crianças saudáveis, estudando a latência e amplitude das ondas, a fim de conhecer as características dos PEAMLs para esta faixa etária. Metodologia: Participaram do estudo 32 crianças de ambos os sexos com idade entre 10 e 13 anos, otologicamente normais e sem histórias neurológicas. A análise estatística incluiu a realização da estatística descritiva (média e desvio-padrão) e análise da variância pelo teste F. Os PEAMLs foram pesquisados utilizando como estímulo tone-burst, nas intensidades de 50, 60 e 70 dBNA. Resultados e conclusão: Os valores médios de latência dos componentes foram Na=20,79ms, Pa=35,34ms, Nb=43,27ms e Pb=53,36ms. Para a amplitude Na-Pa os valores médios obtidos no estudo variaram entre 0,2 e 1,9mV (M=1,0mV). As formas de onda Na-Pa constituíram os componentes mais consistentes e mais facilmente identificáveis. Pode-se concluir que a amplitude aumenta e a latência diminui com o aumento da intensidade sonora. Na intensidade de 50dBNA as latências obtidas são significativamente maiores que as intensidades de 60 e 70 dBNA para a onda Na. A partir de 60dBNA os valores se estabilizam e não há mudanças significativas na latência ou morfologia da onda. Nas comparações inter e intra-individual foram observadas latências mais longas e amplitudes menores para o lado E (A1/Cz). Numa análise posterior dos dados segundo queixa de dificuldade escolar não foram observadas diferenças ao nível de significância para os componentes Na, Pa, Nb e Pb para os grupos de crianças com e sem queixa de dificuldades escolares. Nestas crianças foram observadas anormalidades na morfologia das ondas, as quais não foram atribuídas exclusivamente à queixa de dificuldade escolar, já que poderia haver também interferência da idade do sujeito avaliado e do neuro-desenvolvimento do Sistema Nervoso Auditivo Central. O presente estudo possibilitou um melhor conhecimento das características dos PEAMLs, o que contribuirá para a aplicação mais segura da técnica. Porém, outros estudos ainda se fazem necessários, principalmente na literatura nacional, a fim de estabelecer padrões normativos para o uso na rotina clínica. / Introduction: The record and study of corticals responses evoked by auditory stimulus has allowed the objective investigation from process of auditory information and a better understanding of central auditory path. The utility of the procedure has been valued by audiologists, nevertheless her clinical aplication current demand the a execution a sum more significative of the study, especially in nationals researchs, to knowledge profoundest this procedure, over all as for normative studys, waves?s identification criterion and interference of the variables with age, gender and parameters used in records. The PEAMLs are composed of a waves?s sequence with latency are around 10 a 80ms, with multiple neurogenic origen (thalamus corticais projections and auditory cortex, coliculus inferior and reticular formation in small scale). The present study objetive examined the components dos PEAMLs, in healthy childrens, researching the waves?s latency and amplitude, to know the PEAML in this band of age. Methods: make part of study 32 childrens in both genders between the ages of 10 e 13, normal hearing without neurological desorders. The statistical analises involved the descrition statistical (mean and standard deviation) and variance analises by test F. The PEAMLs are investigated with tone-burst stimuli in 50, 60 e 70 dBNA. Results and conclusions: the means values of the components are Na=20,79ms, Pa=35,34ms, Nb=43,27ms e Pb=53,36ms. To the amplitude Na-Pa the means values obtained in the study varies between 0,2 and 1,9mV (M=1,0mV). The waveforms are more consistents e more easyly identifiable. We are able to conclude that the amplitude increase and latency decrease with growth of intensity of sound. In 50dBNA the latency are significative higher that 60 and 70 dBNA to wave Na. From 60dBNA the values are stabilize and there is no significatives changes in the latency ou morphology of wave. In the comparisions inter e inta-hemisferical were observed latencys lengthest and amplitudes higher to side left (A1/Cz). In a posterior analises in conformity to complaint of hardness scholar were observeds diferrences no significants to the components Na, Pa, Nb e Pb in the childrens groups with and without complaint of hardness scholar. Anormalities in the morphology of waves were viewed in this childrens wich weren´t atribute to complaint of hardness scholar exclusively once there was interference of the patient?s age and the neural development of Central Auditory System Nervous. The present study made possible a better knowledge of PEAMLs and will contribute to securest aplication this procedure. But, another studys still are requisite, essentialy in the researchs national to established normatives standard to utily in the clinical practice.

Electrophysiologic responses are used to estimate hearing thresholds and fit hearing aids in young infants, but these estimates are not exact. An objective test of speech encoding could be used to validate infant fittings by showing that speech has been registered in the central auditory system. Such a test could also show the effects of auditory processing problems on the neural representation of speech. This thesis describes techniques for recording electrophysiologic responses to natural speech stimuli from the brainstem and auditory cortex. The first technique uses a Fourier analyzer to measure steady-state brainstem responses to periodicities and envelope changes in vowels, and the second uses a windowed cross-correlation procedure to measure cortical responses to the envelopes of sentences. Two studies were conducted with the Fourier analyzer. The first measured responses to natural vowels with steady and changing fundamentals, and changing formants. Significant responses to the fundamental were detected for all of the vowels, in all of the subjects, in 19 – 73 s (on average). The second study recorded responses to a vowel fundamental and harmonics. Vowels were presented in opposite polarities to distinguish envelope responses from responses to the spectrum. Significant envelope responses were detected in all subjects at the fundamental. Significant spectral responses were detected in most subjects at harmonics near formant peaks. The third study used cross-correlation to measure cortical responses to sentences. Significant envelope responses were detected to all sentences, at delays of roughly 180 ms. Responses were localized to the posterior auditory cortices. A model based on a series of overlapping transient responses to envelope changes could also account for the results, suggesting that the cortex either directly follows the speech envelope or consistently reacts to changes in this envelope. The strengths and weaknesses of both techniques are discussed in relation to their potential clinical applications.

Electrophysiologic responses are used to estimate hearing thresholds and fit hearing aids in young infants, but these estimates are not exact. An objective test of speech encoding could be used to validate infant fittings by showing that speech has been registered in the central auditory system. Such a test could also show the effects of auditory processing problems on the neural representation of speech. This thesis describes techniques for recording electrophysiologic responses to natural speech stimuli from the brainstem and auditory cortex. The first technique uses a Fourier analyzer to measure steady-state brainstem responses to periodicities and envelope changes in vowels, and the second uses a windowed cross-correlation procedure to measure cortical responses to the envelopes of sentences. Two studies were conducted with the Fourier analyzer. The first measured responses to natural vowels with steady and changing fundamentals, and changing formants. Significant responses to the fundamental were detected for all of the vowels, in all of the subjects, in 19 – 73 s (on average). The second study recorded responses to a vowel fundamental and harmonics. Vowels were presented in opposite polarities to distinguish envelope responses from responses to the spectrum. Significant envelope responses were detected in all subjects at the fundamental. Significant spectral responses were detected in most subjects at harmonics near formant peaks. The third study used cross-correlation to measure cortical responses to sentences. Significant envelope responses were detected to all sentences, at delays of roughly 180 ms. Responses were localized to the posterior auditory cortices. A model based on a series of overlapping transient responses to envelope changes could also account for the results, suggesting that the cortex either directly follows the speech envelope or consistently reacts to changes in this envelope. The strengths and weaknesses of both techniques are discussed in relation to their potential clinical applications.

Introdução: A captação e o estudo de respostas cerebrais evocadas por um estímulo sonoro vem permitindo a investigação objetiva do processamento da informação auditiva e uma melhor compreensão da via auditiva central. A utilidade deste método diagnóstico tem sido cada vez mais valorizada pelos audiologistas, no entanto sua aplicação clínica corrente requer a realização de uma quantidade mais expressiva de estudos, especialmente na literatura nacional, para um conhecimento mais profundo deste método, sobretudo quanto a normatizações, critérios de identificação das ondas e interferências de variáveis como idade, sexo e parâmetros utilizados na aquisição. Os Potenciais Evocados Auditivos de Média Latência são compostos por uma seqüência de ondas com latências em torno de 10 a 80ms, com origem neurogênica múltipla (projeções tálamo-corticais e córtex auditivo, colículo inferior e formação reticular em menor escala). O presente estudo tem como objetivo pesquisar os componentes dos PEAMLs, numa população de crianças saudáveis, estudando a latência e amplitude das ondas, a fim de conhecer as características dos PEAMLs para esta faixa etária. Metodologia: Participaram do estudo 32 crianças de ambos os sexos com idade entre 10 e 13 anos, otologicamente normais e sem histórias neurológicas. A análise estatística incluiu a realização da estatística descritiva (média e desvio-padrão) e análise da variância pelo teste F. Os PEAMLs foram pesquisados utilizando como estímulo tone-burst, nas intensidades de 50, 60 e 70 dBNA. Resultados e conclusão: Os valores médios de latência dos componentes foram Na=20,79ms, Pa=35,34ms, Nb=43,27ms e Pb=53,36ms. Para a amplitude Na-Pa os valores médios obtidos no estudo variaram entre 0,2 e 1,9mV (M=1,0mV). As formas de onda Na-Pa constituíram os componentes mais consistentes e mais facilmente identificáveis. Pode-se concluir que a amplitude aumenta e a latência diminui com o aumento da intensidade sonora. Na intensidade de 50dBNA as latências obtidas são significativamente maiores que as intensidades de 60 e 70 dBNA para a onda Na. A partir de 60dBNA os valores se estabilizam e não há mudanças significativas na latência ou morfologia da onda. Nas comparações inter e intra-individual foram observadas latências mais longas e amplitudes menores para o lado E (A1/Cz). Numa análise posterior dos dados segundo queixa de dificuldade escolar não foram observadas diferenças ao nível de significância para os componentes Na, Pa, Nb e Pb para os grupos de crianças com e sem queixa de dificuldades escolares. Nestas crianças foram observadas anormalidades na morfologia das ondas, as quais não foram atribuídas exclusivamente à queixa de dificuldade escolar, já que poderia haver também interferência da idade do sujeito avaliado e do neuro-desenvolvimento do Sistema Nervoso Auditivo Central. O presente estudo possibilitou um melhor conhecimento das características dos PEAMLs, o que contribuirá para a aplicação mais segura da técnica. Porém, outros estudos ainda se fazem necessários, principalmente na literatura nacional, a fim de estabelecer padrões normativos para o uso na rotina clínica. / Introduction: The record and study of corticals responses evoked by auditory stimulus has allowed the objective investigation from process of auditory information and a better understanding of central auditory path. The utility of the procedure has been valued by audiologists, nevertheless her clinical aplication current demand the a execution a sum more significative of the study, especially in nationals researchs, to knowledge profoundest this procedure, over all as for normative studys, waves?s identification criterion and interference of the variables with age, gender and parameters used in records. The PEAMLs are composed of a waves?s sequence with latency are around 10 a 80ms, with multiple neurogenic origen (thalamus corticais projections and auditory cortex, coliculus inferior and reticular formation in small scale). The present study objetive examined the components dos PEAMLs, in healthy childrens, researching the waves?s latency and amplitude, to know the PEAML in this band of age. Methods: make part of study 32 childrens in both genders between the ages of 10 e 13, normal hearing without neurological desorders. The statistical analises involved the descrition statistical (mean and standard deviation) and variance analises by test F. The PEAMLs are investigated with tone-burst stimuli in 50, 60 e 70 dBNA. Results and conclusions: the means values of the components are Na=20,79ms, Pa=35,34ms, Nb=43,27ms e Pb=53,36ms. To the amplitude Na-Pa the means values obtained in the study varies between 0,2 and 1,9mV (M=1,0mV). The waveforms are more consistents e more easyly identifiable. We are able to conclude that the amplitude increase and latency decrease with growth of intensity of sound. In 50dBNA the latency are significative higher that 60 and 70 dBNA to wave Na. From 60dBNA the values are stabilize and there is no significatives changes in the latency ou morphology of wave. In the comparisions inter e inta-hemisferical were observed latencys lengthest and amplitudes higher to side left (A1/Cz). In a posterior analises in conformity to complaint of hardness scholar were observeds diferrences no significants to the components Na, Pa, Nb e Pb in the childrens groups with and without complaint of hardness scholar. Anormalities in the morphology of waves were viewed in this childrens wich weren´t atribute to complaint of hardness scholar exclusively once there was interference of the patient?s age and the neural development of Central Auditory System Nervous. The present study made possible a better knowledge of PEAMLs and will contribute to securest aplication this procedure. But, another studys still are requisite, essentialy in the researchs national to established normatives standard to utily in the clinical practice.

This work investigated the effects of various stressors on auditory speech processing using speech-evoked auditory brainstem response (ABR). This work was carried out in three distinct studies: (1) the effects of stimulus rate and noise on the speech-evoked ABR, (2) the effects of direct, early, and later-arriving speech reflections on the speech-evoked ABR, and (3) the effects of self-masking and overlap masking in a reverberant environment using speech-evoked ABR. Results from the first study indicate a complex interaction of fast stimulus rate and noise on the speech-evoked ABR. In particular, dissociation was found between electrophysiological responses to the envelope and the responses to the temporal fine structure or transient waves. The main finding from the second study is that direct sound and early reflections produce similar speech-evoked ABR, while the response to late reverberation shows different characteristics. Results from the third study indicate that severe reverberation significantly weakened the ABR when compared to anechoic or moderate reverberation, while moderate reverberation significantly enhanced the ABR when compared to anechoic speech. Overall, the new findings from this research shed light on the effects of stressors such as noise, increased stimulus rate, and reverberation. Up until now, these effects have mostly been studied perceptually. Our research demonstrates that these effects can be studied electrophysiologically using speech-evoked brainstem responses. This method of investigation permits the probing of particular stages of the auditory pathway and evaluating how neural activity in response to specific elements of speech, such as the fundamental frequency and formants, is affected by different stressors.

Ménière’s disease (MD) is an idiopathic inner ear disorder, characterised by episodes of vertigo, tinnitus, sensorineural hearing loss, and aural fullness in the affected ear. The relatively high variability of symptomological changes renders it difficult to confirm the MD diagnosis. The purpose of this study is to compare the diagnostic power of an instrumental method, electrocochleography (ECochG), and two subjective methods, including the criteria based on the clinical guidelines provided by the American Academy of Otolaryngology-Head and Neck Surgery Committee on Hearing Equilibrium (AAO-HNS CHE) and Gibson’s Score. A quota sampling method was used to include subjects. A total of 250 potential MD patients who were referred to the Department of Otolaryngology at the Christchurch Hospital between year 1994 and 2009 have had their signs and symptoms documented and ECochG testing completed. A selection of details obtained from both AAO-HNS CHE and ECochG assessment results were examined as a chart review in regard to its function as a diagnostic tool for MD. The between-method reliability was found to be high, with a few disagreements on individual diagnosis. Based on a receiver operating characteristic (ROC) curve analysis, the ECochG measures were shown to be pertinent to the diagnosis of MD. It was also found that patients tested “positive”, as compared with those tested “negative”, tended to show higher correlations among the four key symptoms of MD and among the ECochG measures derived from the auditory evoked responses to tone bursts at frequencies in close proximity to each other.

Made available in DSpace on 2016-04-27T18:12:20Z (GMT). No. of bitstreams: 1 TALITA SUNAITIS DONINI.pdf: 559650 bytes, checksum: 953e8e48e9b5f5b3b8408d2a27a85b2a (MD5) Previous issue date: 2007-02-22 / The implementation of Universal Newborn hearing screening aims at earlier diagnosis and intervention for hearing impaired children. The use of hearing aids is one of the most important elements of the intervention process focused on the development of oral language. Brainstem evoked auditory response - ABR using click or frequency specific tone bursts have limitations in terms of presenting the stimulus in free field. The use of Auditory Steady State Response- ASSR in early diagnosis and hearing aid evaluation has been referred in the literature and appears to be promising for obtaining minimal levels of response for children that are not able to give behavioral auditory responses, particularly aided responses in free field. The goal of the study was to discuss the responses of hearing impaired children obtained with ASSR in free field, within the different audiological procedures for verification and validation of the prescribed eletroacoustic characteristics of the hearing aids. Results on the ASSR of six children with severe hearing loss were analyzed . These children were enrolled at the Educational Audiology Program of at The Center for Hearing in Children at DERDIC- PUCSP, and were regular hearing aid users. All subjects had: pure tone audiometry and ASSR with phones and in free field aided and unaided. Correlations were obtained between different conditions in order to discuss the possible contributions of the ASSR in the evaluation of hearing aids benefit. There was a strong correlation between the response levels obtained in the aided free field audiometry and aided free field ASSR. The correlation was weaker under the earphone condition probably due to the degree of hearing loss of the subjects that participated in the study. There seems to be a good potential for the use of free field aided responses using SSR in clinical conditions as an additional information on hearing aid benefit / A implantação dos programas de Triagem Auditiva Neonatal Universal têm o objetivo de promover ao diagnóstico da deficiência e a intervenção terapêutica fonoaudiológica o mais cedo possível. A seleção e adaptação de aparelhos de amplificação sonora (AASI) constituem parte importante do processo de intervenção dentro de uma perspectiva de desenvolvimento da linguagem oral. Os dados obtidos por meio dos registros do potencial evocado auditivo de tronco encefálico com utilização dos estímulos clique e freqüência específica possuem algumas limitações na obtenção do registro. Desta forma, destaca-se o uso do Potencial Evocado Auditivo de Estado Estável (PEAEEst) como um procedimento que possibilita obter limiares eletrofisiológicos em diferentes freqüências, de forma simultânea, o que reduz o tempo de teste e provê informações essenciais para a seleção e adaptação de AASI. Assim, o objetivo deste estudo foi discutir a utilização do registro do potencial evocado auditivo de estado estável em campo livre no processo de indicação de aparelhos de amplificação sonora para crianças com deficiência auditiva, como parte do conjunto dos procedimentos de verificação e validação das características prescritas.. Foram analisados os registros do PEAEEst de crianças e adolescentes usuárias de AASI atendidas pelo Serviço de Audiologia Educacional e pelo Centro Audição na Criança - DERDIC, portadores de deficiência auditiva de grau severo. Foram avaliados os resultados da audiometria tonal e potencial evocado auditivo de estado estável obtidos com fones e em campo livre com uso de amplificação. Os dados obtidos foram analisados estatisticamente a fim de discutir as contribuições do uso do PEAEEst no processo de indicação de AASI de sujeitos com deficiência auditiva. Observamos que há correlação entre os achados da audiometria tonal em campo livre e o PEAEEst obtido em campo livre com AASI. Na comparação entre os registros obtidos na audiometria tonal e PEAEEst realizados com fones observamos menor correlação. Algumas características como grau e configuração da perda auditiva pareceram interferir no registro do potencial. A utilização clínica deste procedimento pode promover informações importantes sobre as respostas da criança com uso dos aparelhos de maneira objetiva

Während seiner normalen Funktion generiert das Gehirn starke elektrische Signale, die technisch gemessen werden können. Das schon seit über einem Jahrhundert bekannte Phänomen ermöglicht es die Signalverarbeitung im Gehirn räumlich und zeitlich zu beobachten. Heute versteht man die zellulären Prozesse die zur Generierung der elektrischen Signale in einzelnen Neuronen führen. Jedoch rekrutieren die meisten neuronalen Ereignisse große Populationen von Zellen, dessen Aktivität zeitlich und räumlich koordiniert ist. Diese Koordinierung führt dazu, dass ihre elektrische Aktivität auch weit von den Quellen gemessen werden kann, sodass die Beobachtung des Gehirns auch nicht invasiv auf der Schädeloberfläche mittels dem sogenannten Elektroenzephalogramm (EEG) möglich ist. Der zeitliche Verlauf des Signals hängt nicht nur von den Eigenschaften einzelner Zellen ab sondern auch von ihrer Wechselwirkung mit anderen Neuronen, die oft komplex oder gar nicht bekannt ist. Diese Komplexität verhindert die Auswertung der gemessen Signale im Bezug auf die Anzahl von aktiven Neuronen, die Art der Antwort (Inhibition, Exzitation), die Synchronisationsstärke und den Einfluss anderer aktiver Prozesse (wie zum Beispiel: Lernen, Aufmerksamkeit usw.). In dieser Arbeit werden die Zusammenhänge zwischen diesen mikroskopischen Parametern (einzelne Neurone) und ihrer makroskopischen Wirkung (EEG) experimentell, datenanalytisch und theoretisch untersucht. / During its normal function the brain generates strong and measurable electric signals. This phenomenon, which has been known for more than a century, makes it possible to investigate the signal processing in the brain. Nowadays the cellular processes taking part in the generation of the electric signals are well understood. However, most of the neuronal events recruit large populations of cells, whose activities are coordinated spatially and temporally. This coordination allows for summation of activities generated by many neurons leading to extracellular electric signals that can be recorded non-invasively from the scalp by means of electroencephalography (EEG). The temporal structure of the EEG signal does not depend only on the properties of single neurons, but also on their interactions that may be very complex. The complexity hinders the evaluation of the recoded signal with respect to the number of active neurons, the type of response, the degree of synchronisation and the contribution of other processes (such as, learning and attention). In the thesis, the relations between the microscopic (single-neuron) and their macroscopic (EEG) properties will be investigated by means of experimental, data-analytic and theoretical approaches.

Die Überwachung des zentralen Nervensystems (ZNS) während der Allgemeinanästhesie ist aus anästhesiologischer Sicht wünschenswert, um eine Über- oder Unterdosierung von Narkotika intraoperativ zu vermeiden. Narkosetiefe wird definiert als die Summe aller intraoperativ auf den Patienten einwirkenden sensorischen Stimuli und den zentralnervös dämpfenden Effekten der Anästhetika auf die zerebrale Aktivität. Während für die akustisch evozierten Potentiale diskutiert wird, ob sie die hypnotische Komponente der Allgemeinanästhesie erfassen, ist derzeit unklar, welchen Beitrag somatosensorisch evozierten Potentialen bei der Bestimmung von Narkosetiefe leisten können. Somatosensorisch evozierte Potentiale werden in der klinischen Routine zur Überwachung der Integrität von neuronalen Leitungsbahnen bei Operationen eingesetzt. Das Ziel der hier vorgestellten klinischen Untersuchungen, in denen somatosensorisch und akustisch evozierte Potentiale (SEP, AEP) als mögliche Parameter zur Quantifizierung von Narkosetiefe gegenübergestellt werden, bestand darin, nachfolgende Hypothesen zu überprüfen: 1. Die mittleren Komponenten von SEP und AEP verändern sich dosisabhängig in Abhängigkeit vom Narkotikum in Amplituden und Latenzen und eignen sich als Parameter zur Quantifizierung von Narkotikawirkungen auf das ZNS. 2. Die durch Anästhetika induzierten Veränderungen von SEP und AEP sind unter chirurgischer Stimulation reversibel. Daher eignen sich SEP und AEP als Parameter zur Quantifizierung von Narkosetiefe. 3. SEP und AEP sind geeignet, bei kritisch kranken Patienten den Grad der Analgosedierung quantitativ zu erfassen. 4. SEP und AEP lassen Rückschlüsse auf die Modulation kognitiver Prozesse unter Narkotika zu. In mehreren klinischen Studien an narkotisierten oder analgosedierten Patienten (n = 161) wurden die Wirkungen von Anästhetika auf SEP und AEP dokumentiert, bzw. der Einfluß von chirurgischen oder pflegerischen Maßnahmen untersucht. Zielvariablen waren die Mittellatenz-Komponenten der SEP (N20, P25, N35, P45, N50) und der AEP (Na, Pa; Nb) im Vergleich zur klinischen Einschätzung der Narkosetiefe und den hämodynamischen Daten. Die statistische Analyse wurde mittelts multivariater Analysen durchgeführt, die prädiktive Aussagekraft anhand der prediction probability nach Smith berechnet. Unter Anästhetikagabe fand sich als grundlegendes Muster sowohl bei den SEP als auch bei den AEP eine Verlängerung der Latenzen bei Verminderung der korrespondierenden Amplituden, wobei die Effekte auf die späteren Komponenten > 35 ms deutlicher ausgeprägt waren. Während der Aufwachphase aus der Anästhesie, unter chirurgischen und pflegerischen Maßnahmen waren die anästhetikabedingten Veränderungen der EP-Komponenten teilweise reversibel. Darüberhinaus ließen die SEP-Latenzen P45 und N50 und die AEP-Latenz Nb während der Aufwachphase aus der Anästhesie Rückschlüsse auf die Wiederkehr des expliziten Erinnerungsvermögens nach Narkose zu. Im Gegensatz zu signifikanten Effekten im Gruppenvergleich war die prädiktive Aussagekraft der EP-Parameter im Individualfall gering. SEP sind unter den hier gewählten Narkotikaregimes geeignet, die Modulation der zerebralen Aktivität unter Anästhetika abzubilden. Im Sinne kortikaler Arousalreaktionen werden unter exogener Stimulation die durch Anästhetika induzierten Veränderungen der SEP teilweise antagonisiert. Bei der Interpretation der Befunde in Hinblick auf den Grad der Narkosetiefe ist zu berücksichtigen, daß die Effekte nicht unabhängig vom Anästhetikum sind und im Individualfall stark variieren können. Dennoch ist im Einzelfall der Einsatz von SEP als Monitor zur Narkosetiefe durchaus sinnvoll, z. B. wenn AEP oder andere Verfahren nicht durchführbar sind. Ein Einsatz der SEP als "idealer" Monitor zur Bestimmung des Grades der Narkosetiefe in der klinischen Routine ist zum jetzigen Zeitpunkt sicher nicht gerechtfertigt. Zweifelsohne können weitere Untersuchungen mit SEP zu wesentlichen Erkenntnissen in der klinisch anästhesiologischen Grundlagenforschung beitragen. / Monitoring of the functional state of the central nervous system is of major concern for the anaesthetist to avoid over- or undermedication with the possible sequelae for the patient during general anaesthesia. Depth of anaesthesia is defined as the sum of all excitatory stimuli during operation and the depressant effects of anaesthetics on the electrical activity of the brain. Currently it is discussed, whether the auditory evoked responses (AER) reflect the hypnotic component during anaesthesia. In contrast there is limited information about somatosensory evoked responses (SER) with respect to depth of anaesthesia, even though SER are used to monitor the integrity of the somatosensory pathway at risk during surgery. The aim of the present clinical investigations, in which SER and AER were investigated as parameters to quantify depth of anaesthesia, was to test the following hypotheses: 1. Anaesthetics induce dose-related changes in somatosensory and auditory evoked responses and quantify the anaesthetic action on the brain. 2. During surgical stimulation the anaesthetic induced changes are reversed in part. Therefore SERs and AERs are indicators of depth of anaesthesia. 3. SERs and AERs quantify the grade of analgosedation in critically ill patients. 4. SERs and AERs indicate modulation of cognitive function during recovery from anaesthesia. In clinical studies (n = 161 patients) we investigated the midlatency components of SER and AER during different anaesthetic drug combinations, their modulation during surgical stimulation or nursing care and during recovery from anaesthesia. The midlatency SER components N20, P25, N35, P45 and N50 and the AER components Na, Pa and Nb were studied in relation to the clinical assessment of anaesthetic depth and haemodynamic parameters. Statistical analyses were performed by multivariate analyses of variance for repeated measurements and by the calculation for the prediction probability according to Smith. Results: The main pattern of anaesthetic induced changes on midlatency SER and AER waves was as follows: Prolongation in the latencies and reduction of the corresponding amplitudes. The effect was more pronounced on the components > 35 ms. During recovery from general anaesthesia, during surgical stimulation or nursing care the anaesthetic induced changes were in part reversed. Moreover, changes of the SER components P45 and N50 and the AER component Nb differed in patients with respect to explicit memory performance during the wake-up phase from general anaesthesia. While the group effects were significant, the calculated values of the prediction probability indicated a low predictive potency for the individual case. Conclusions: The midlatency SER waves are indicative for changes in the electrical brain activity during different anaesthetic drug combinations. During surgery or other types of exogeneous intervention the anaesthetic induced changes of some SER and AER components are reversed indicating cortical arousal. Interpreting the results with respect to measure depth of anaesthesia it is important to know, that the changes of the evoked responses are dependent on the used anaesthetic and may differ markedly inter- and intraindividually. In a single case SER-recording can be useful to monitor anaesthetic depth, if e.g. AER monitoring is not possible. However, at the present time SER are not advocated as an "ideal" monitor to measure the level of anaesthesia during clinical routine. Without doubt further investigation elucidating the relation between SER and anaesthetics will contribute to our basic understanding of anaesthetic action on the brain.

Evoked potentials are electric brain response to external stimulus. They are important diagnostic no visual method in neurology. For their excitation use of different of kinds stimulation, most often: visual, auditory, somatosenzory, olfactory and gustatory. Evoked potentials are objective method for measurement sense perception. This master’s thesis is specialized to auditory evoked potentials and design acoustic generator for their stimulation. Auditory evoked potentials are primary used for objective audiometry, but they have another usage. In the first place, application is specialized on health sector. The aim of this master’s thesis is compact specified medical requirements with available technical resources.