How Does a Cochlear Implant Work?

Cochlear implant technology uses cochlear implants as a treatment for severe deafness to total deafness. Cochlear implant is an electronic bionic device developed according to the principles of cochlear physiology. It is a multi-disciplinary high-tech product combining audiology, medicine, biomedicine, microelectronics, materials science and mechanics. The cochlear implant can replace the damaged hearing organ. The external speech processor converts the sound into a certain coded electrical signal and transmits it to the human cochlea. The electrode system implanted in the body stimulates the auditory nerve fibers distributed there and directly excites the auditory nerve. To restore or rebuild the hearing function of the deaf. Cochlear implants are one of the important achievements of modern medicine. For mild to moderate hearing loss, hearing aids can have a good compensation effect. For severe or very severe deafness, cochlear implantation is currently recognized internationally as a The only effective device to restore hearing in patients with bilateral severe or very severe sensorineural hearing loss. In recent years, with the development of electronic technology, computer technology, phonetics, electrophysiology, materials science, and ear microsurgery, cochlear implants have entered clinical applications from experimental research.

Cochlear implant technology uses cochlear implants as a treatment for severe deafness to total deafness. Cochlear implant is an electronic bionic device developed according to the principles of cochlear physiology. It is a multi-disciplinary high-tech product combining audiology, medicine, biomedicine, microelectronics, materials science and mechanics. The cochlear implant can replace the damaged hearing organ. The external speech processor converts the sound into a certain coded electrical signal and transmits it to the human cochlea. The electrode system implanted in the body stimulates the auditory nerve fibers distributed there and directly excites the auditory nerve. To restore or rebuild the hearing function of the deaf. Cochlear implants are one of the important achievements of modern medicine. For mild to moderate hearing loss, hearing aids can have a good compensation effect. For severe or very severe deafness, cochlear implantation is currently recognized internationally as a The only effective device to restore hearing in patients with bilateral severe or very severe sensorineural hearing loss. In recent years, with the development of electronic technology, computer technology, phonetics, electrophysiology, materials science, and ear microsurgery, cochlear implants have entered clinical applications from experimental research.

Chinese name

Cochlear implant technology

Use

Treatment of severe deafness to total deafness

Attributes

Medical treatment technology

Device

Cochlear implant

Cochlear implant

Cochlear implants (also known as bionic ears, cochlear implants, and cochlear implants) are implanted hearing aids whose function is to make patients with severe hearing loss (deaf) produce certain sound perception. Unlike other types of hearing aids, such as hearing aids, the working principle of a cochlear implant is not to amplify the sound, but to apply pulsed electrical stimulation to the intact auditory nerve located in the cochlea. Most cochlear implant devices consist of an implanted part and an extracorporeal part. The external part consists of a microphone, a voice ^[1] processor, and a signal transmitter for sending instructions to the implanted part. The implanted part is composed of a signal receiving and decoding module and a stimulation electrode array.

History of cochlear implant technology

The history of cochlear implants dates back at least 200 years. Italian scientist Alessandro Volta invented the battery, and the voltage unit Volt was named after him. He used the battery as a research tool to prove that electrical stimulation can directly stimulate the human body's hearing, sight, smell, and tactile perception. When he put the positive and negative poles of a 50 volt battery close to the ears, he felt: "... the moment the circuit was switched on, I felt my head was shaken, and after a while I started to hear a This kind of sound, or a kind of noise, I can't describe exactly: it is a crackling sound with electric sparks, it seems that something sticky is boiled ... This terrible feeling makes me afraid to continue Repeat this experiment because I think the electric shock to the brain is dangerous ... "In the following 150 years, there were no reports of safe and systematic research on the electrical stimulation effect of the auditory system until the advent of modern electronic technology. In 1937, SSStevens and colleagues used vacuum tube oscillators and amplifiers to confirm at least three mechanisms related to "electroacoustic perception." The first mechanism is the "electromechanical effect", which specifically refers to the electrical stimulation of the ciliary cells in the cochlea to vibrate, so that a person feels a tone information at the frequency of the acoustic stimulation signal corresponding to the electrical stimulation. The second mechanism is that the eardrum converts electrical signals into acoustic signals, so that people can feel another tone information at 2 times the signal frequency. Stevens et al. Were able to separate the second mechanism from the first because they found that patients with broken or missing tympanic membranes could only perceive tone signals at the original frequency. The third mechanism is related to the direct electrical excitation of the auditory nerve, because some patients report that they feel noise-like sounds in the sinusoidal electrical excitation signal, which has a dramatic increase in loudness with current changes, and often causes facial nerve excitement. However, the earliest demonstration of the electrical stimulation effect of the auditory nerve was by a group of Russian scientists who claimed to have observed the hearing perception of a patient with middle and inner ear deafness under electrical stimulation.

In 1957, French doctor Djourno and others successfully used electrical stimulation to produce hearing sensation in two completely deaf patients. Their success stimulated a series of in-depth studies in the West Coast of the United States to restore hearing to deaf patients in the 1960s and 1970s. Although the methods of earlier research are primitive compared to current technology, they point out many key issues and some of the constraints that must be considered in order to successfully implement electrical auditory nerve stimulation. For example, they found that the dynamic range of the electroacoustic hearing of the auditory nerve is much smaller than that of the acoustic hearing, and that the sound changes dramatically, and the time-domain tones are limited to a few hundred hertz. Bilger explained and analyzed these early experiments in detail. In 1972, the first sound processor supporting the single-channel cochlear implant was introduced. In 1977, the Austrian developed the world's first multi-channel cochlear implant system. In 1978, Australian Gram Clark invented the world's first Cochlear implants. It proves that humans have successfully explored electrical stimulation alternative devices in the entire human world. After decades of development, especially with the emergence of new and high technologies such as biomedical engineering in recent years, cochlear implantation has entered clinical applications from experimental research and has become the only effective treatment to restore hearing in deaf patients. According to statistics, more than 30,000 deaf patients worldwide now use cochlear implants.

In commercial terms, the House-3M single-electrode cochlea became the first FDA-certified cochlear device in 1984 and has hundreds of users. The University of Utah has also developed a set of 6-electrode cochlea with perforated pins, which also has hundreds of users. This device from the University of Utah is known in the literature as the Ineraid or Symbion device, which is well adapted to the needs of experimental applications. The Laura system developed by Antwerp University in Belgium can transmit 8-channel bipolar or 15-channel unipolar stimulation information. The MXM laboratory in France has also developed a 15-channel unipolar device, the Digisonic MX20. These products were gradually phased out.

It was led by Wang Zhengmin, Professor of Eye, Otorhinolaryngology Hospital, Fudan University and Academician of the Chinese Academy of Sciences. It lasted 18 years, and successfully developed a single-channel pulse cochlear implant and a single-channel continuous cochlear implant. The multi-channel program-controlled cochlear implant of intellectual property rights and independent innovative technologies has broken the monopoly of the cochlea. The clinical effects and various data indicators have reached the international advanced level, which has enabled China to enter the world. Many countries develop and produce cochlear implants.

At the same time, in the inner ear world with a total volume of less than 1 cubic centimeter, Academician Wang Zhengmin also made three world firsts: the first to use the micro-endoscopic laser system to discover ten new lesions in the inner ear; the first to transform the artificial cheekbones; the first to use the service system to reduce Otitis media treatment of facial paralysis. At the same time, he took the lead in developing ear-skull base surgery and facial neurosurgery in China with a success rate close to 100%, allowing China's ear surgery to go hand in hand with developed countries.

Cochlear Implant Technology System Composition

Cochlear implant is a high-tech electronic device that can completely replace damaged inner ear hair cells. It can convert external sounds into electrical nerve pulse signals, bypass necrotic hair cells in the auditory system, and directly stimulate the spiral of the auditory nerve. Ganglia, which sends information to the brain. With severe hearing loss, cochlear implants are the only hope and choice for deaf patients.

As shown in Figure 6, the following procedure briefly introduces the working process of a cochlear implant:

(a) The microphone on the speech processor collects sound.

(b) Information is passed to the speech processor.

(c) The speech processor digitizes, filters, and encodes sounds, and analyzes and encodes them into special forms of digital information.

(d) Send the coded signal to the transmission coil via a wire.

(e) The transmission coil transmits the coded signal to a receiver / stimulator under the skin.

(f) The receiver / stimulator decodes the encoded signal.

(g) Electronic signals are sent to specific locations in the electrode series to stimulate nerve fibers in the cochlea.

(h) The auditory nerve receives electrical signals and transmits them to the auditory center of the brain. The brain recognizes these electrical signals as sound.

Although the design of the various components of a cochlear implant may vary from manufacturer to manufacturer, the overall working principle is the same. For example, the microphone can be hooked on the upper ear or pinned to the chest. The shape, color, and radio frequency value of the transmission coil can be different, but the magnetic coupling structure is exactly the same.

Cochlear Implant Speech Processing Solutions

At the end of the 1970s, the University of Utah developed the first multi-channel cochlear implant device that became a commodity. Its voice processor divides the sound into 4 different channels, and then compresses the analog signal output from each channel to adapt to the narrow electrical stimulation. Small dynamic range. This speech processing scheme is called analog compression (CA).

In the early 1980s, the University of Melbourne, Australia developed a Nucleus cochlear implant device with 22 intra-snail electrodes. The design idea of Nucleus' speech processor is to extract important speech features, such as the fundamental frequency and formants, and then pass them to the corresponding electrodes by encoding. The Nucleus processor is characterized by bi-phase pulses, bipolar stimulation, stimulating different electrodes in a time-sharing manner, and the stimulation frequency does not exceed 500 Hz. The speech processing solution from the initial extraction of only the fundamental frequency and the second formant (F0F2) information, to the WSP processor (F0F1F2) with the first formant, F0F1F2 plus the multipeak processor with three high-frequency peaks (multipeak), To date, only a peakpeak processor that extracts any of the 6 highest energy frequency information in 22 analysis bands.

The continuous interval sampling (CIS) speech processor studied by Wilson et al. Contrary to Nucleus's feature extraction design philosophy, the CIS processor tries to preserve the original information in the speech, divides the speech into 4 to 8 frequency bands and extracts the waveform envelope information of each frequency band, and then uses the logarithmic function to perform dynamic range compression, and uses high The frequency bi-phase pulse continuously samples the compressed envelope, and finally sends the burst with the speech envelope information to the corresponding electrodes at intervals. From the perspective of information content, CIS and CA processors are basically the same, but the advantage of CIS is that it avoids the electric field interference caused by the simultaneous stimulation of multiple electrodes. Although CIS and Nucleu both use biphasic pulse interval stimulation, they have the following two differences: First, each electrode of the CIS uses a high-frequency (800-2000Hz) pulse train for constant and continuous stimulation, even if The same is true when there is no sound, except that the pulse amplitude drops to a threshold level. Second, the analysis frequency band of CIS and the number of stimulation electrodes are the same. At present, the CIS speech processing scheme has been widely adopted by most cochlear implant companies in the world, and based on this New improvements have been made. For example, the American ABC company introduced the S series processing solution, the Australian Nucleus company introduced the CI24M 24-channel device ACE solution and the Austrian MEDEL company introduced the fast CIS solution.

Cochlear Implantation Surgery

General anesthesia was used for surgery, and intravenous drip antibiotics were given before the incision. Electrode impedance testing and nerve response telemetry (NRT) were performed after the electrodes were implanted. Special cases such as inner ear malformation use EBAR monitoring and facial nerve monitoring. Facial crypt approach is mostly adopted in the surgical approach. Behind the ear is generally used. The incision is divided into two layers, the surface layer is the skin and subcutaneous tissue, and the deep layer is the temporal fascia and periosteal flap. The entire flap is turned back, exposing the cortex of the mastoid area. A receiver / stimulator bone bed was made on the skull surface above and behind the mastoid with an electric drill. A simple mastoidectomy was performed to expose the short anvil bones, which was used as a sign to open the recess of the face. The stimulator was placed into the bone bed, the stimulation electrode was inserted into the cochlear drum stage, and the reference electrode was placed on the surface of the skull below the temporal muscle. The cochlear deformity (such as Mondini deformity, common cavity deformity) and cochlear ossification cases should be modified accordingly. Surgical complications include wound infection, flap necrosis, facial paralysis, meningitis, and electrode prolapse. A small number of patients with cochlear implanted electrodes had mild vertigo after surgery and mostly disappeared within a few days.

Indications for cochlear implant technology

Cochlear implant technology for pre-speech deaf patients

(1) The hearing loss range of children with severe or extremely severe sensorineural hearing loss in both ears is 1 kHz and higher, and the hearing threshold is above 90 dB. For those who have no residual hearing before surgery, a hearing aid sound field audiometry is needed to help determine the residual hearing and, if necessary, an electrical stimulation auditory brainstem evoked potential (EABR) test.

(2) The etiology is unknown, congenital, hereditary, medicinal, hearing loss after meningitis, and the lesion is localized in the cochlea; in patients with acoustic neuropathy, the lesion is localized in the cochlea, and preoperative EABR examination is required to estimate the lesion site. From the medical point of view, the risk of hearing neuropathy needs to be informed to the parents of the child. For most inner ear malformations, including Mondini malformations, common cavity malformations, and large vestibular aqueduct malformations are still indications for cochlear implantation, parents of children need to be informed of the particular risks and parents have reasonable expectations.

(3) Time of deafness For newly occurring hearing loss, it is necessary to observe stable hearing changes for at least 3 months.

(4) The optimal age should be 12 months to 5 years; subject to the limitations of brain hearing and speech plasticity, cochlear implants should be implanted as soon as possible. Children or adolescents over 5 years of age need a certain listening and language foundation, and a history of hearing aid wearing and hearing or language training from an early age. Hearing aids are ineffective or perform poorly, meaning that the open sentence recognition rate is 30% or the two-word recognition rate is 70% under the best hearing-aid listening environment.

(5) No significant improvement in hearing ability after the selection of hearing aids. Wear appropriate hearing aids, and no significant improvement in hearing and language skills after 3 to 6 months of hearing rehabilitation training.

(6) Have normal mental and intellectual development.

(7) The family and / or implanter have a correct understanding and appropriate expectations of the cochlear implant.

(8) Conditions for hearing and speech rehabilitation education.

(9) No contraindications to surgery.

Cochlear implant technique for deaf patients

(1) Hearing loss in adults with binaural severe or very severe sensorineural hearing loss ranges from 1 kHz and higher and the hearing threshold is above 70 dB. For those who have no residual hearing before the operation, a hearing aid sound field audiometry is needed to help determine the residual hearing, and if necessary, an EABR examination or a psychophysical test of the drum-point electrical stimulation is performed.

(2) Candidates for elderly cochlear implantation in post-deaf deaf patients of all ages need to have a correct understanding of cochlear implants and appropriate expectations.

(3) Time of deafness For newly occurring hearing loss, it is necessary to observe stable hearing changes for at least 3 months.

(4) There was no significant improvement in speech recognition after hearing aids were selected.

(5) Have normal psychological and mental conditions, and patients have a correct understanding of cochlear implants and appropriate expectations.

(6) No contraindications to surgery.

Contraindications of cochlear implant technology

Absolute contraindications for cochlear implant technology

(1) Cases of severe inner ear malformation, such as Michel malformation or cochlea absent;

(2) The absence of the auditory nerve;

(3) severe mental illness;

(4) Pyogenic inflammation of the mastoid process in the middle ear has not been controlled.

Relative contraindications for cochlear implant technology

(1) The general condition of the whole body caused by the accompanying disease is poor.

(2) Uncontrolled epilepsy.

(3) Patients with white matter lesions are not contraindications for cochlear implantation, but the parents of the child must be informed of the special risks and the parents have reasonable expectations.

(4) Secretory otitis media and gum ears are not contraindications to surgery. For patients with chronic otitis media and perforation of the tympanic membrane, if the inflammation is controlled, one-stage or staged surgery can be selected.

Preoperative evaluation of cochlear implant technology

Medical history collection of cochlear implant

Understand the cause through history collection and examination. The collection of otological history should focus on the causes and processes of deafness, and the patient's hearing history, tinnitus and vertigo history, history of ototoxic drug exposure, history of noise exposure, history of systemic acute and chronic infections, past history of ear diseases, Developmental factors (general or local malformation, mental development, etc.), family history of deafness, hearing aid wearing history, and other causes, such as epilepsy, mental condition, etc. Deaf children should also include: mother's pregnancy history, pediatric birth history, pediatric growth history, speech development history, and so on. You should also understand the patient's language skills (such as pronunciation characteristics, articulation intelligibility) and language understanding and communication skills (such as oral, lip reading, sign language, written, guessing, etc.).

Cochlear Implant Cochlear Examination

Including ear Guo, external ear canal, tympanic membrane and eustachian tube.

(1) Audiological examination: subjective hearing threshold measurement can be used in children under 6 years of age, including behavioral observation audiometry, visual enhanced audiometry and game audiometry; acoustic impedance measurement including tympanic pressure curve And stapedius reflexes; 40Hz-related potentials (or multi-frequency steady-state evoked potentials) of auditory brainstem response (ABR); otoacoustic emissions (transiently induced otoacoustic emissions or distortion products otoacoustic emissions); speech test Hearing speech threshold test is speech perception threshold and speech recognition threshold; speech recognition test includes speech test vocabulary and pediatric speech test vocabulary; Hearing aids must be equipped with a professional hearing engineer for hearing aids. Generally, both ears are required Hearing aid hearing threshold test and speech recognition test should be performed, followed by auditory language training for 3 to 6 months; vestibular function test (those with a history of vertigo); Drum Cape electrical stimulation test test including threshold, dynamic range, frequency discrimination , Interval discrimination and time course discrimination.

(2) Evaluation criteria of audiology: The pure-tone air conduction threshold of post-speech deaf patients is> 80dBHL (average value of 0.5, 1, 2, and 4kHz, WHO standard). If good ears can help open short sentence recognition to less than 30%, and hearing loss is greater than or equal to 75dB, you can consider using cochlear implants [see US Food and Drug Administration (FDA) supplementary standards]; pre-speech deaf patients For infants and young children, a number of guest observations and behavioral assessments are required to conduct a comprehensive evaluation, including: no auditory response (120dBSPL) when ABR checks the acoustic output; no response when the maximum acoustic output is above 2kHz at a frequency of 40Hz related potential detection, below 1kHz Frequency> 100dB; Multi-frequency steady-state audiometry above 2kHz has no response at 105dBHL; distortion products otoacoustic emissions have no response at both frequencies; helpful for sound field audiometry above 2kHz, the hearing threshold does not enter the auditory language area (banana chart), speech The recognition rate (two-word) score is less than 70%, confirming that the child cannot get effective help from the hearing aid; For patients without any residual hearing, such as those who have a clear hearing response to the electrical stimulation of the drums, can still consider cochlear implantation surgery. If there is no auditory response to Gushen electrical stimulation, the patient or parent should be informed, and the patient and family should consider the risk of surgery.

Cochlear Implant Evaluation

Imaging examination is the most important examination for patients. Thin-layer CT scan of the temporal bone, three-dimensional reconstruction of the cochlea, and magnetic resonance examination of the inner ear canal should be routinely performed, and skull magnetic resonance examination should be performed if necessary.

Cochlear Implant Language Proficiency Assessment

Speech proficiency assessment (language structure and function) should be performed on patients with certain language experience or ability, including speech intelligibility, vocabulary, comprehension ability, grammatical ability, expression ability and communication ability; for children under 3 years old and uncooperative , The method of video observation of "parent-child games" was used to evaluate, so as to judge the current language ability of patients.

Cochlear Implant Evaluation

For children over 3 years of age who lack language skills, the Hines Learning Ability Test can be selected, and for those under 3 years of age, the Griffith Mental Developmental Behavior Test can be used. Patients with suspected mental retardation (Hine's learning ability assessment IQ <68 points, Griffith test mental development quotient <70 points) or patients with abnormal psychological behavior should be advised to go to an authoritative institution for further observation, diagnosis and Identification. Cochlear implants may be considered for those with socio-cultural mental retardation; for patients with socio-cultural retardation, or with ADHD, autism, and other mental and intellectual developmental disorders, parents should be made aware that such diseases may provide patients with postoperative rehabilitation It brings great difficulties to help parents establish objective psychological expectations.

Cochlear Implant Evaluation

Get a full physical examination and related auxiliary examinations.

Cochlear Implant Technology for Family Condition Assessment

Families who have received professional training or are regularly instructed by a language training teacher can conduct hearing and language training for children at home, otherwise they should be sent to a deaf rehabilitation school or institution.

Cochlear implant adjustment after implantation

Switch-on was performed one month after cochlear implantation. Due to different design principles of different cochlear implants, the tuning hardware and software used are different, and the tuning method, tuning process and tuning parameters are also different. Cochlear implants include implants in the body and speech processors outside the body. Mapping (mapping) is the process of adjusting the parameters in each cochlear implant device by a professional through a computer and special equipment to provide the patient with the most comfortable and effective stimulation and allow the patient to hear various sounds comfortably. Unless a professional sets appropriate values in a series of parameters through tuning, the speech processor will not work. The parameters that need to be adjusted after cochlear implantation include: speech coding schemes such as SPEAK, CIS, and ACE schemes; electrical stimulation modes, including unipolar stimulation, bipolar stimulation, and common ground mode; the channels used can be selected from 1 to 22 channels, the frequency distribution of the filtered output of the channel, the frequency range of 200Hz to 8kHz is assigned to each channel; the threshold value of each channel (the minimum stimulation level at which T value can produce auditory stimulation); the maximum comfortable stimulation of each channel (C Value for the greatest comfort stimulus the patient can feel).

The start-up is scheduled for 3 to 5 weeks after surgery. At this time, the internal part of the cochlear implant, especially the electrode part, is relatively stable. After turning on, most patients will have a gradual adaptation process to the external sound. After a period of psychological and physiological changes and development, they can stabilize. During the first 1 to 4 weeks after power-on, the electrode parameters have the largest and fastest changes. They are debugged once a week, once every two weeks in the second month, once a month in the third month, and every three months thereafter. Six months, once a year.

Rehabilitation after cochlear implantation

Patients, parents of deaf children and teachers should be made aware of the importance of auditory and speech rehabilitation training after cochlear implantation, especially how to prepare for postoperative deaf children and how to choose a rehabilitation location. Preoperative rehabilitation training should be implemented according to the characteristics of different children's age and hearing language level. The content of rehabilitation training should focus on the establishment of the patient's hearing consciousness and understanding of the concept definition of things. It should be used for postoperative commissioning and rehabilitation training. Good behavior experience and psychological preparation for learning.

The "Speaking Oral Training Method" is a logical and strict guiding principle. For children with cochlear implants, it refers to a training method that uses the signals of the cochlear implant to maximize the development of hearing and then develop oral language to create the best environment for them. Deaf children's hearing and speech training should conform to the language development law of children, and should be carried out gradually from shallow to deep according to the "hearing age" of deaf children. It is roughly divided into three stages, namely the auditory training stage, the vocabulary accumulation stage, and the language training stage.

Cochlear implant hearing training stage

The hearing training stage mainly uses the residual hearing of the deaf children to listen to various sounds, awakens their "sleeping state", and often gives stimulation, repeated training and repeated strengthening, so that the deaf children gradually adapt to the daily sounds and enter the sound society.

Cochlear implant vocabulary accumulation stage

The vocabulary accumulation stage is based on hearing training, supplemented by visual and other sensations to let them know more social things, combining what they see and touch with sound signals to form signals in their brains, so that they gradually understand the meaning of speech.

Cochlear implant language training stage

The language training stage is based on the accumulation of vocabulary. Deaf children are trained to speak more, from single words to short sentences, from simple to complex, from small to many. Gradually, they can understand the language of others, so that others can understand themselves. Language.

Cochlear implant rehabilitation should be implemented under the guidance of professionals, and service agencies that undertake professional rehabilitation guidance provide appropriate rehabilitation training models for hearing impaired children and families.

Cochlear Implantation Progress

The emergence of cochlear implants has brought the gospel to patients with severe hearing impairment. At present, more than 120,000 people worldwide have received cochlear implants, and most patients have returned to the world of sound after surgery. Some developed countries in Europe and the United States have cancelled some deaf schools, cochlear implants have been included in medical insurance, and some countries such as Germany can even perform bilateral cochlear implants free of charge. With the further development of technology, the effect of cochlear implants has further improved, and the quality of products has also improved significantly. At the same time, the surgical technique has also been greatly improved, the surgical complications have been significantly reduced, and the scope of surgical indications has gradually expanded. The original relative contraindications, such as acoustic neuropathy and white matter disease, have also achieved good results after cochlear implantation. The rehabilitation conditions have also been significantly improved, and the rehabilitation effect has been significantly improved.

Cochlear implantation for bilateral implantation

Since the first bilateral cochlear implant in Europe in 1996, the number of bilateral cochlear implants has grown rapidly. Unilateral cochlear implantation has achieved better speech recognition, but clinical studies have suggested that bilateral implantation has significant gains in sound source localization and speech recognition in complex auditory environments. The research results on bilateral implantation mainly focus on the following aspects: Implanters who use the existing cochlear implant system have improved speech recognition rate in quiet and noise background after bilateral implantation In addition, the implanter's ability to locate the sound source has also been strengthened to a certain extent; the quality of the hearing of the bilateral implanter has been improved; and the age of bilateral implantation, the report shows that the age of the implanter is more than 3 After the age, the brain can still integrate the reconstructed bilateral signal input; some bilateral implanters have faster speech development, but this phenomenon still needs to be controlled; electrophysiological experiments suggest that early bilateral implantation promotes bilateral The best method for the development of lateral auditory pathways; bilateral implanters can also accept new coding strategies (fine structure coding strategies) and obtain more detailed and richer hearing, and thereby promote sound source localization, complex or stereo hearing The ability to analyze speech in context. Because cochlear implants are expensive, most patients currently undergo unilateral cochlear implants. The effectiveness of bilateral cochlear implants over unilateral ones has been widely recognized. In addition to further improving speech recognition rate, another advantage of bilateral implantation is that it provides safety guarantee in the future. Most of the side where the cochlear implant is not implanted will cause hearing deprivation, resulting in atrophy of the auditory pathway. When the cochlear implant is re-implanted, if the original surgical implantation side cannot be successfully implanted due to various reasons, it is still difficult to see the effect of the contralateral reimplantation. Expected. The existing knowledge suggests that the contralateral side is not used for a long time, and even if the implantation can be effective in the future, it will take a long time to achieve the best results (about 3 years), which will obviously affect the quality of life of patients. Therefore, families with economic conditions are best to choose bilateral implants.

Coding Implantation Strategy Improvement

At present, the coding strategies of mainstream cochlear implant systems are based on the continuous interleaved sampling (CIS) strategy. The CIS coding strategy realizes the coding of the sound amplitude by sampling the overall contour (that is, the envelope of the sound signal and the amplitude of the sound wave) of the output of each band of the band-pass filter. The limitation of the CIS coding strategy is that it fails to encode the instantaneous frequency change information contained in low-frequency and some intermediate-frequency sound waves, while normal human cochlea can encode the above information by "phase locking". At present, some cochlear implant systems have a fine structure coding strategy, which can encode the instantaneous frequency change information contained in low-frequency and some intermediate-frequency sound waves. Existing clinical studies have compared the effect of fine structure coding and CIS coding on the auditory gain of implanters. The above research suggests that the improvement of the fine structure coding strategy on the gain involves the following aspects: recognition of vowels, consonants, and monosyllabic words; speech recognition in quiet and noisy backgrounds; and the ability of the implanter to perceive music. The co-progression of cochlear coding technology with electrode design and implantation technology has promoted the improvement of the hearing of the implanter. From the initial single-channel cochlear implant to the multi-channel cochlear implant, from the CIS coding strategy to the fine structure coding strategy, the core of cochlear implant technology progress has always focused on better coding strategies and more accurate cochlear stimulation.

Cochlear implant technique

Some deaf patients can gain hearing gain from combined acoustic and electrical stimulation technology. Some deaf patients (light to moderate hearing loss in the low frequency region but extremely severe hearing loss in the high frequency region, and the audiogram shows a steep decline) It is difficult to obtain good hearing gain with traditional hearing aids, that is, it is difficult for hearing aids to provide satisfactory Hearing, and cochlear implants may damage the patient's residual hearing in the low frequency region when the electrodes are implanted. Since the first implantation in 1999, a number of combined acoustic-electric stimulation implants have been performed in Europe. Acoustic-electrical stimulation, that is, to provide sound signal stimulation to the low frequency region of the cochlea, and to provide electrical signal stimulation to the high frequency region, in order to obtain a good auditory reconstruction. Acoustic-electrical stimulation is based on the following technologies: round window implantation technology: round window implantation can protect residual hearing to a greater extent; electrode design: special electrodes are used during implantation to cover high-frequency and some intermediate-frequency areas; Speech processor: encodes low-frequency and high-frequency signals separately through independent parallel signal processing paths. After implantation of acousto-electrical stimulation, the patient usually obtains the best hearing gain after a period of time (3-6 months). This postoperative recovery period suggests that it takes time for the auditory center to recognize, be familiar with, and integrate the two signals (sound and electrical signals).

Cochlear implant technology is effective at young age

China and the United States set the minimum age for cochlear implantation after 12 months. However, recent studies have found that the sooner the cochlear implant is implanted, the better the results after surgery. Therefore there is no upper or lower age limit for European cochlear implants.

Improvement of cochlear implant surgery technique

In recent years, the concept of soft surgery and minimally invasive surgery has gradually been introduced. Minimally invasive surgery is not just a small incision, but also emphasizes minimally invasive windowing and minimally invasive implantation. Minimally invasive windowing and implantation techniques help preserve low-frequency residual hearing. With the successful development of the new electrode (EAS), the advantages of round window implantation have been re-recognized again: to avoid damage to the basement membrane caused by cochlear drilling; the round window membrane remains intact before the electrode implantation, and the electrode During implantation, the round window membrane surrounds the electrode to form a good seal, reduces lymphatic overflow, maximizes protection of the drum-level microenvironment, prevents bone meal and blood from entering, and reduces infection of the inner ear caused by electrode insertion. The most natural angle to ensure accurate entry into the drum step and reduce inner ear damage; Paprocki believes that the round window implantation has increased the length of the bone spiral plate by 2mm compared with the opening of the drum promontory, which means that the contact between the electrode and the snail axis has increased. More ganglion cells are stimulated by electrodes.

Problems with cochlear implant technology

Although the existing cochlear implant products have been able to return patients to the world of sound, so that patients can get basically normal hearing, after hearing and speech rehabilitation training, most of them can perform auditory speech communication without obstacles, but the sound provided by cochlear implants Still unable to reproduce the real sound 100%. If the sound is distorted, the pleasant music may become unpleasant, just like the sound after the tape is partially demagnetized, so the patient still cannot enjoy the music like a healthy listener. A large-scale survey conducted in Europe in 2002 showed that after 16 years of cochlear implantation, more than 95% of adults and 91% of children continue to use the original product. In addition to the failure of the cochlear implant itself, there are other reasons for replacement. Some of the patients were replaced because of product upgrades or replacement of cochlear implants of different brands. From this statistics, the performance of existing cochlear implant products is very guaranteed. Although the product design of a cochlear implant is a lifetime design, it is an electronic product after all, and it is difficult to guarantee that it will not be bad for decades. The human ear can hear 0-100dB sound, and the sound pressure level can reach 1010, which is 100 million level, while the cochlear implant produces hearing through electrical stimulation. The excessive current causes pain, so the dynamic range of the cochlear implant is only 104, which is obviously inferior to that of a hearing person.