Fortunately, electrical stimulation can be delivered without external, middle or indeed even an inner ear. In the earlier chapters of this book the auditory system has been described in some detail, including pathology that can result in the most debilitating degrees of hearing loss: severe to profound deafness. This provides some esthetic advantage but may fall off more easily and compromises sound collection. In some of today’s CI systems the sound processor and RF coil are a single component held in place by the magnet but having no wire or BTE part.
Hence the implant consists of: its receiver coil, a hermetic package containing electronic circuits and an electrode lead assembly connecting to the electrode array that is placed inside the cochlea ( Figure 3). The RF signal provides both power for the implant’s electronics and the information needed to produce electrical stimulation.
#Free estim software skin#
This arrangement supports reliable communication across the skin through the use of RF based telemetry. The external coil is held in place over the implant’s receiver coil through a pair of magnets: one external and one within the surgically implanted device under the skin. Except in the case of one-piece processors, a lead connects the sound processor output to a radio frequency (RF) transmitter coil located above and behind the ear. The sound is first “cleaned” to remove noise and then processed to create the stimulation patterns destined for the implanted electrode array. Sound is typically collected from microphones housed on a behind the ear (BTE) sound processor. Even where speech understanding is limited, a release from the isolation of deafness through access to environmental sounds, a reduction in the level of tinnitus and support of lip-reading with a reduction in the effort required for oral communication are all worthwhile benefits from use of a CI. It should also be noted that in many cases those most satisfied with their implant are not those who receive the highest scores on standardized tests of speech understanding.įigure 2 shows the various components common to all of today’s clinically applied cochlear implant systems. In the best of cases, CI users can make fluent use of a telephone, understand speech in adverse listening conditions where there is considerable competing noise and reverberation, hence enjoying independence spanning social lives and careers that would have been unimaginable without their CI device. Today over half a million people, from babies under 6 months of age to adults in their late 90s, have been implanted with a CI. While it can be argued that the CI is the most successful medical device ever created, the outcomes are still highly variable ( Figure 1).
The early devices that were produced in academic institutions were transferred to commercial organizations, these often building on prior medical device experience, for example experience gained in the pace maker field. While many of these pioneers suffered ridicule at the hands of the mainstream scientific community, clinical considerations prevailed.
During the two decades following this work, various clinical studies saw the implantation of single and then multi-channel cochlear implant (CI) systems in people suffering profound deafness. However, the forerunner of a modern CI system is just over 60 years old: opportunistic stimulation of the auditory nerve of a bilaterally deaf patient receiving a facial nerve graft. When Volta applied 50 volts to his own head, he reported hearing an unpleasant boiling sound. From the beginning to current practiceĮlectrical stimulation of the human auditory system is generally traced back to the pioneering experiments of Alessandro Volta, inventor of the battery. Research that is likely to bring medium term benefits to the clinical application of cochlear implants will also be described.ġ.
Alternative devices such as auditory brainstem implants will be described, and additionally the more experimental auditory mid-brain implants and intraneural stimulation approaches. Today’s variety of patient will be reviewed: unilaterally and bilaterally implanted, bimodal users of a cochlear implant as well as a contralateral hearing aid, CROS device users having either asymmetrical hearing loss or single-sided deafness. The challenges involved in the design and application of cochlear implants will be outlined, including the programming of clinical systems to suit the needs of implanted patients. This chapter will describe how electrical stimulation manages to compensate for sensory-neural hearing loss by bypassing the damaged cochlea. In many healthcare systems electrical stimulation of the human auditory system, using cochlear implants, is a common treatment for severe to profound deafness.
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