Cochlear Implants: Fundamentals and Application - part 1 potx

Cochlear Implants: Fundamentals and Application Graeme Clark Springer COCHLEAR IMPLANTS This page intentionally left blank COCHLEAR IMPLANTS Fundamentals and Applications Graeme Clark The University of Melbourne and The Bionic Ear Institute, East Melbourne, Victoria, Australia With 244 Illustrations Graeme Clark Department of Otolaryngology and The Bionic Ear Institute The University of Melbourne 348-388 Albert Street East Melbourne, Victoria 3002 Australia g.clark@unimelb.edu.au Series Editor: Robert T. Beyer Department of Physics Brown University Providence, RI 02912 USA Library of Congress Cataloging-in-Publication Data Clark, Graeme. Cochlear implants : fundamentals and applications / Graeme Clark. p. cm. — (Modern acoustics and signal processing) Includes bibliographical references and index. ISBN 0-387-95583-6 (alk. paper) 1. Cochlear implants. 2. Deaf—Rehabilitation. I. Title. II. AIP series in modern acoustics and signal processing. RF305.C536 2003 617.8Ј9—dc21 2002030584 ISBN 0-387-95583-6 Printed on acid-free paper. ᭧ 2003 Springer-Verlag New York, Inc. AIP Press is an imprint of Springer-Verlag New York, Inc. All rights reserved. This work may not be translated or copied in whole or in part without the written permission of the publisher (Springer-Verlag New York, Inc., 175 Fifth Avenue, New York, NY 10010, USA), except for brief excerpts in connection with reviews or scholarly analysis. Use in connection with any form of information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed is forbidden. The use in this publication of trade names, trademarks, service marks, and similar terms, even if they are not identified as such, is not to be taken as an expression of opinion as to whether or not they are subject to proprietary rights. Printed in the United States of America. 987654321 SPIN 10892784 www.springer-ny.com Springer-Verlag New York Berlin Heidelberg A member of BertelsmannSpringer ScienceםBusiness Media GmbH This book is dedicated to my wife, Margaret, for her selfless support and wise counsel during the last 35 years while I was undertaking cochlear implant research at the University of Sydney, the University of Melbourne, and The Bionic Ear Institute. I would like also to express my appreciation to our children Sonya, Cecily, Roslyn, Merran, and Jonathan; their spouses Ian, Peter, and Marissa; and our grandchildren Elise, Monty, Daniel, Noah, and Rebekah for their encourage- ment and enriching our lives. I have been very impressed by the emergence of the bionic ear as a practical proposition, but even more by the promise for the future that it seems to embody. It makes use of the arrangement in the cochlea for pitch recognition to bring electronic technology into direct functional relationship with the nervous system and the hu- man consciousness. Maybe that unique relationship has no other parallel in the nervous system, and thus that direct link between electronics and physiology will find no other application to medi- cine. Nevertheless, I feel it may represent a new benchmark in the understanding of neural and mental function in terms of their physi- cal components. —Professor Emeritus Sir Macfarlane Burnett, A.K., O.M., K.B.E., M.D., Ph.D., Lond., F.A.A., F.R.S., Nobel Laureate (Physiology or Medicine)—The First Patron of the Bionic Ear Institute, 1985 Series Preface Soun is nought but air y-broke —Geoffrey Chaucer end of the 14th century Traditionally, acoustics has formed one of the fundamental branches of physics. In the twentieth century, the field has broadened considerably and become in- creasingly interdisciplinary. At the present time, specialists in modern acoustics can be encountered not only in physics departments, but also in electrical and mechanical engineering departments, as well as in mathematics, oceanography, and even psychology departments. They work in areas spanning from musical instruments to architecture to problems related to speech perception. Today, six hundred years after Chaucer made his brilliant remark, we recognize that sound and acoustics is a discipline extremely broad in scope, literally covering waves and vibrations in all media at all frequencies and at all intensities. This series of scientific literature, entitled Modern Acoustics and Signal Pro- cessing (MASP), covers all areas of today’s acoustics as an interdisciplinary field. It offers scientific monographs, graduate-level textbooks, and reference materials in such areas as architectural acoustics, structural sound and vibration, musical acoustics, noise, bioacoustics, physiological and psychological acoustics, speech, ocean acoustics, underwater sound, and acoustical signal processing. Acoustics is primarily a matter of communication. Whether it be speech or music, listening spaces or hearing, signaling in sonar or in ultrasonography, we seek to maximize our ability to convey information and, at the same time, to minimize the effects of noise. Signaling has itself given birth to the field of signal processing, the analysis of all received acoustic information or, indeed, all infor- mation in any electronic form. With the extreme importance of acoustics for both modern science and industry in mind, AIP press, now an imprint of Springer- Verlag, initiated this series as a new and promising publishing venture. We hope that this venture will be beneficial to the entire international acoustical commu- nity, as represented by the Acoustical Society of America, a founding member of vii viii Series Preface the American Institute of Physics, and other related societies and professional interest groups. It is our hope that scientists and graduate students will find the books in this series useful in their research, teaching, and studies. As James Russell Lowell once wrote, “In creating, the only hard thing’s to begin.” This is such a beginning. Robert T. Beyer Series Editor-in-Chief ix Preface The cochlear implant is a device that bypasses a nonfunctional inner ear and stimulates the hearing nerves with patterns of electrical currents so that speech and other sounds can be experienced by profoundly deaf people. It is the cul- mination of investigations that started in the 19th century, and as such it is the first major advance in helping profoundly deaf children to communicate since the sign language of the deaf was developed at the Paris Deaf School 200 years ago. It is also the first direct interface to the central nervous system to restore sensory function for use on a regular clinical basis. I became interested in helping deaf people hear when I was 10 years old, because my father had a severe hearing loss and I knew how difficult it was for him to cope as a pharmacist and as a family man. In 1966 I left my practice as an ear, nose, and throat surgeon in Melbourne to do research and to learn how it might be possible to help people with a profound hearing loss. These were the patients I had to turn away from my clinic, saying that a hearing aid would be of little help but that one day medical research might provide an alternative. For me this meant first undertaking basic studies to learn about the differences between acoustic and electrical stimulation of the auditory neural pathways. When it became clear from these and other basic studies that the best chance of providing speech understanding was through multiple electrode stimulation, many scientific challenges were to lie ahead. As previous attempts to produce speech understanding with electrical stimulation had been unsuccessful, and as reproducing the coding of sound was not seen as feasible, the research faced rigorous scientific criticism. The first criticism came from auditory neuroscience, where research had shown the complexity of the inner ear and central brain path- ways. Not surprisingly it was believed that inserting a relatively small number of electrodes into the inner ear to stimulate groups of nerve fibers would fail to produce sufficient information for speech understanding. The second criticism came from the biological and clinical disciplines. Here the concern was that im- plantation would damage the very nerves it was intended to stimulate. In addition, it was thought the electrode could be a pathway for middle ear infection to induce [...]... Pathways 14 0 Spiral Ganglion .14 0 Cochlear Nucleus 14 1 Pons and Midbrain 14 2 Human Brainstem 14 3 Prenatal (Congenital) and Postnatal Hearing Loss 14 4 Genetic and Chromosomal .14 4 Acquired 14 8 References 15 1 4 Neurobiology 16 0 Overview 16 0 Definition of Terms 16 0 Current and Charge 16 0 Voltage .16 1 Resistance... Experimental Animal 10 4 Contents xvii Tissue Responses in the Human 10 9 Bio-compatibility of Materials 11 2 Methods of Investigation 11 2 Tissue Response 11 3 Infection 11 6 Otitis Media 11 6 Labyrinthitis and Meningitis 11 7 Experimental Animal Studies 12 2 Host Factors and Foreign Bodies 13 6 Clinical Protocol 13 9 Deafness and the Central... Resistance 16 1 Capacitance 16 1 Impedance 16 1 Electrode/Tissue Interface 16 2 Polarization 16 2 Charge Transfer .16 2 Charge Density 16 3 Equivalent Circuits .16 3 Impedance 16 5 Corrosion-Stimulus Parameters 16 8 Mechanisms 16 8 Stimulus Parameters .16 9 Scanning Electron Microscope Evaluation of Electrodes .17 1 Electrical... Objections and Questions .xxxiii Answers to the Fundamental Objections xxxiv 1 A History 1 Pre-science 1 Eighteenth Century 1 Nineteenth Century 3 Twentieth Century 3 19 00 to 19 30s: Early Hearing Aids 3 19 30s to 19 40s: Initial Indirect Electrical Stimulation in the Human 4 19 50s to 19 60s: Initial Direct Electrical Stimulation in the Human 6 19 60s: Fundamental... 86 Cochlear Nucleus 87 Superior Olivary Complex 89 Lateral Lemniscus 91 Inferior Colliculus 91 Superior Colliculus 92 Medial Geniculate Body 92 Auditory Cortex 93 References 93 3 Surgical Pathology 10 0 Inflammation 10 0 Classification .10 1 Etiology .10 1 Pathophysiology 10 1 Insertion Trauma 10 4... Adults and Children 696 References 697 12 Results 707 Aims .707 Development of Tests 707 Speech and Sound Perception: Test Principles 708 Variability of Materials and Responses .708 Prerecorded Versus Live Voice 709 Training Effects and Experience . 710 Closed-Set Tests 710 Speech Features (Consonants and Vowels) 712 Open-Set Tests 713 ... of Stimulation 18 3 Chronic Studies on the Effects of High Rates of Stimulation 18 7 Electrical Stimulation of the Cochlear Nucleus 18 9 Acute Studies on the Effects of Low Rates of Stimulation 18 9 Chronic Studies on the Effects of Low Rates of Stimulation 18 9 References 19 0 5 Electrophysiology 19 9 General Neurophysiology 19 9 Action Potentials 19 9 Strength-Duration Curves... into the Inner Ear) 608 Insertion of Arrays 612 Sealing the Opening . 617 Perilymph “Gusher” . 618 Fixing the Electrode Array and Receiver-Stimulator . 619 Flap and Wound Closure 620 Radiology 620 Postoperative Care .6 21 Complications and Management 6 21 Intraoperative Complications 6 21 Postoperative Complications 623 Special Cases ... Parameters and Neural Stimulation 17 2 Electrochemically Safe Stimulus Parameters .17 2 Charge Density and Charge per Phase .17 3 Biochemical Effects 17 3 Neural Preservation 17 4 Electrical Stimulation of the Cochlear Nerve 17 5 Acute studies on the Effects of Low Rates of Stimulation .17 5 xviii Contents Chronic Studies on the Effects of Low Rates of Stimulation 17 6 Acute... Speech Reading . 714 Speech Tracking 715 Speech in Noise 716 Environmental Sounds 717 Test Batteries 717 Questionnaires . 718 Bimodal and Bilateral Speech Processing 718 Speech Production: Test Principles 720 Imitative and Spontaneous Speech 720 Computer Aided Speech and Language Assessment procedure (CASALA) .7 21 Contents xxiii Language: . Human 10 9 Bio-compatibility of Materials 11 2 Methods of Investigation 11 2 Tissue Response 11 3 Infection 11 6 Otitis Media 11 6 Labyrinthitis and Meningitis 11 7 Experimental Animal Studies 12 2 Host. (Congenital) and Postnatal Hearing Loss 14 4 Genetic and Chromosomal 14 4 Acquired 14 8 References 15 1 4. Neurobiology 16 0 Overview 16 0 Definition of Terms 16 0 Current and Charge 16 0 Voltage 16 1 Resistance 16 1 Capacitance. 16 1 Capacitance 16 1 Impedance 16 1 Electrode/Tissue Interface 16 2 Polarization 16 2 Charge Transfer 16 2 Charge Density 16 3 Equivalent Circuits 16 3 Impedance 16 5 Corrosion-Stimulus Parameters 16 8 Mechanisms