hearing aid

Hearing aid fitting is a complex of research, technical and pedagogical measures aimed at improving the hearing function for the social rehabilitation of hearing-impaired persons and improving their quality of life. This is an individual selection, adjustment of hearing aids and adaptation of the patient to its use.

A hearing aid is a special electronic-acoustic device, which is a kind of prosthesis for the organ of hearing, designed to amplify sound. Indications for hearing aid fitting are determined by the degree of hearing loss for sounds related to the speech frequency zone (512-4096 Hz). It has been established that the range of the most effective use of hearing aids in intensity calculation is limited by hearing loss in the specified frequency zone within the range of 40 to 80 dB. This means that with a hearing loss of less than 40 dB, prosthetics are not yet indicated, with a hearing loss of 40-80 dB, the use of hearing aids is indicated, and with a hearing loss of more than 80 dB, prosthetics are still possible.

Indications for electroacoustic hearing correction are determined by an audiologist, and individual selection of hearing aids is performed by a technical worker based on the audiometry data obtained during the patient's examination at an audiologist's appointment. These data include information on the patient's perception of whispered and spoken language, tonal and speech audiograms, and, if necessary, information on speech intelligibility and noise immunity, the level of auditory discomfort, etc.

Hearing aid fitting is indicated only in case of bilateral hearing loss, and in case of asymmetric hearing loss the hearing aid is used on the better hearing ear. This achieves the maximum effect with minimal sound amplification, which is of no small importance for more effective adaptation to the use of the device. The question of the effect of long-term use of a hearing aid on hearing seems to be quite significant. Among some categories of doctors and patients there is an opinion that the use of a hearing aid causes deterioration of residual hearing. However, numerous studies and observations have shown that long-term use of the device not only does not worsen hearing, but on the contrary, in some cases it improves by 10-15 dB. This phenomenon can be explained by the phenomenon of disinhibition of the auditory centers, which occurs due to the receipt of more intense impulses to them when the sound is amplified.

The best option for hearing aids is binaural hearing aids, which is especially important when hearing aids are used for children. This is due to the fact that sound information coming from the right and left ears is processed by the left and right hemispheres, respectively, so with bi-ear prosthetics, the prerequisites for the full development of both hemispheres of the brain are created. In addition, with binaural prosthetics, the ototopic function is significantly improved and the need for significant sound amplification is reduced. Binaural hearing significantly increases the noise immunity of the sound analyzer, the selectivity of the direction of the useful signal, and reduces the harmful effects of high-intensity noise on the hearing organ.

Hearing aids. The history of using technical means of sound amplification to improve hearing in the case of hearing loss goes back many hundreds (if not thousands) of years. The simplest "device" for improving the perception of the speech of an interlocutor by a hearing-impaired person is the palm of the hand, applied to the auricle in the form of a horn, which achieves a sound amplification of 5-10 dB. However, such amplification is often enough to improve speech intelligibility with a hearing loss of less than 60 dB. The famous Italian scientist Girolamo Gardano, who lived in the 16th century, described a method for improving hearing with the help of a well-dried wooden rod clamped between the teeth, which, resonating with surrounding sounds, ensured their flow to the cochlea via bone conduction. Ludwig van Beethoven, who suffered from progressive hearing loss, composed musical works, holding a wooden rod in his teeth, resting its other end on the lid of the piano. This actually proves that the composer had a hearing impairment of the conduction type, which is usually observed in OS. This fact refutes the legend about the luetic origin of the deafness of this greatest composer. The Beethoven Museum in Bonn contains numerous acoustic devices made especially for him. This was the beginning of the so-called acoustic sound amplification devices. In the following years, numerous acoustic devices were proposed in the form of auditory trumpets, horns, horns, etc., which were used to amplify sound in both air and tissue sound conduction.

A new stage in the improvement of artificial improvement of the hearing function came with the invention of electrical devices for generating, amplifying and transmitting sound vibrations over a distance using wires. This was due to the inventions of A.G. Bell, professor of speech physiology at Boston University, creator of the first electric hearing aid. Since 1900, their mass production began both in America and in Europe. The development of radio electronics led to the creation of amplifiers first on radio tubes, then on semiconductor devices, which ensured the improvement and miniaturization of hearing aids. Much work was done in the direction of both improving the acoustic characteristics of the hearing aid and in the field of design. Models of pocket devices were developed, in the form of hairpins built into spectacle frames, etc. Behind-the-ear hearing aids, which allow compensating for almost any hearing loss, have become the most widespread in Russia. These devices differ from each other in size, gain, frequency response, operational controls and various additional functional capabilities, such as connecting the hearing aid to a telephone.

Hearing aids are divided into pocket, behind-the-ear, in-the-ear, in-the-canal and implantable. According to the principle of the device - into analog and digital.

Pocket hearing aids are attached to the patient's clothing. All parts of these devices, except for the telephone, are located in a separate block, which contains a microphone, amplifier, frequency filter and power supply element, as well as controls. The converted, interference-filtered and amplified electrical analogue of sound is transmitted via a connecting cable to the telephone, fixed on the insert in the external auditory canal. The design solution of a pocket hearing aid, consisting in the fact that the microphone and telephone are separated by tens of centimeters, allows achieving significant sound amplification without the appearance of acoustic feedback, manifested by generation (whistle). In addition, this design of the hearing aid allows for binaural hearing aids, which significantly improves the quality of sound perception, speech intelligibility and returns the patient's spatial hearing function. The dimensions of the device allow for the introduction of additional functions into its circuit, controlled by the corresponding non-operative regulators. In addition to typical pocket hearing aids, there are also hearing aids in the form of glasses, hearing aids in the form of clips, etc.

Behind-the-ear hearing aids make up the majority of models used by patients. They are small in size and have a cosmetic advantage over pocket hearing aids, as they are placed in the behind-the-ear area, often covered by a lock of hair. Their design provides for the placement of all functional elements of the circuit in one block, and only a short sound-conducting tube with an olive insert at the end is inserted into the external auditory canal.

In-the-ear and in-the-canal hearing aids are optimal in cosmetic terms, since the entire structure is placed in the initial sections of the external auditory canal and is practically unnoticeable during normal communication with the patient. In these devices, the amplifier with the microphone and telephone is partially (in-the-ear model) or completely (in-the-canal model) placed in an ear mold individually made from a mold of the external auditory canal, which ensures complete isolation of the telephone from the microphone and prevents parasitic acoustic "tie-up".

Modern hearing aids have the ability to selectively amplify in different areas of the sound spectrum, up to 7.5 kHz, which allows signal intensity to be increased at frequencies where the greatest hearing loss occurs, thereby achieving uniform perception of sounds across the entire audible frequency spectrum.

Programmable hearing aids. The principle of the device of these devices is based on the presence of a microcircuit on which several programs are recorded for different modes of operation of the hearing aid: speech perception in normal everyday conditions or in conditions of extraneous sound interference, talking on the phone, etc.

Digital hearing aids are analogs of mini-computers, in which the time and spectral analysis of the input signal is carried out, in which the individual characteristics of a given form of hearing loss are taken into account with the appropriate adjustment to the input useful and parasitic sound signals. Computer technology allows to significantly expand the ability to control the output signal by intensity and frequency composition even in ultra-miniature in-the-ear models.

Implantable hearing aids. A model of such an apparatus was first used in the USA in 1996. The principle of the device is that a vibrator (analogous to a telephone), generating sound vibrations, is fixed on an anvil and sets it into vibrations corresponding to the input signal, the sound waves of which then spread in their natural way. The vibrator is connected to a miniature radio receiver implanted under the skin in the behind-the-ear area. The radio receiver picks up radio signals from a transmitter and amplifier placed outside above the receiver. The transmitter is held in the behind-the-ear area by a magnet placed on the implanted receiver. To date, fully implantable hearing aids have been developed without any external elements.

Cochlear implantation. This method is the latest development for the rehabilitation of hearing in adults and children with significant hearing loss or deafness (acquired or congenital), who are no longer helped by conventional or vibroacoustic devices. These patients include those in whom it is impossible to restore airborne sound conduction and the use of bone sound devices is ineffective. Usually, these are patients with a congenital defect of the auditory receptors or with irreversible damage to them resulting from toxic or traumatic injury. The main condition for the successful use of cochlear implantation is the normal state of the spiral ganglion and auditory nerve, and the overlying auditory centers and conduction pathways, including the cortical zones of the sound analyzer.

The principle of cochlear implantation is to stimulate the axons of the auditory (cochlear) nerve with electric current impulses, which encode the frequency and amplitude parameters of sound. The cochlear implantation system is an electronic device consisting of two parts - external and internal.

The external part includes a microphone, a speech processor, a transmitter of radio frequency waves containing electromagnetic analogues of the sound received by the microphone and processed by the speech processor, and a transmitting antenna, a cable connecting the speech processor to the transmitter. The transmitter with the transmitting antenna is attached to the behind-the-ear area using a magnet installed on the implant. The implanted part consists of a receiving antenna and a processor-decoder that decodes the received signal, forms weak electrical impulses, distributes them according to the corresponding frequencies and directs them to a chain of stimulating electrodes that are inserted into the cochlear duct during the operation. All the implant electronics are located in a small hermetically sealed case that is implanted in the temporal bone behind the ear. It does not contain power elements. The energy required for its operation comes from the speech processor along the high-frequency tract along with the information signal. The contacts of the electrode chain are located on a flexible silicone electrode carrier and are located phonotopically in accordance with the spatial position of the anatomical structures of the SpO. This means that the high-frequency electrodes are located at the base of the cochlea, the mid-frequency ones in the middle, and the low-frequency ones at its apex. There can be from 12 to 22 such electrodes transmitting electrical analogues of sounds of different frequencies. There is also a reference electrode, which serves to close the electrical circuit. It is installed behind the ear under the muscle.

Thus, the electrical impulses generated by the entire cochlear implant system stimulate various sections of the axons of the spiral ganglion, from which the fibers of the cochlear nerve are formed, and it, performing its natural functions, transmits nerve impulses to the brain along the auditory pathway. The latter receives nerve impulses and interprets them as sound, forming a sound image. It should be noted that this image differs significantly from the input sound signal, and in order to bring it into line with the concepts reflecting the surrounding world, persistent and long-term pedagogical work is required. Moreover, if the patient suffers from deaf-mutism, then even more work is needed to teach him speech acceptable for understanding by others.

Methodology of hearing aid fitting. In terms of method, hearing aid fitting is a complex task that places strict demands on the selection of electroacoustic parameters of a hearing aid that are adequate to the condition and compensatory capabilities of the patient's residual hearing. Such parameters primarily include thresholds of hearing sensitivity in the speech frequency zone, levels of uncomfortable and comfortable loudness, and the dynamic range in the speech frequency zone. Methods for establishing these parameters include psychoacoustic and electrophysiological methods, each of which has its own methods of quantitative processing and analysis of diagnostic conclusions. Of decisive importance in these conclusions are the calculation of the required amplification of the output signal and the correction of hearing loss by frequency. Most calculation methods use thresholds of hearing sensitivity and thresholds of comfortable and uncomfortable signal perception. The main principle of selecting a hearing aid - according to A.I. Lopotko (1998) is:

1. Different people with hearing loss require different types of electroacoustic hearing correction;
2. it is necessary to take into account certain relationships between the individual frequency values of the patient's hearing characteristics and the electroacoustic characteristics of the hearing aid, ensuring optimal rehabilitation;
3. the amplitude-frequency characteristic of the inserted gain cannot be simply a mirror image of the threshold characteristic of individual hearing, but must take into account both the psychophysiological characteristics of the perception of sound of different frequencies and intensities (masking phenomena and FUNG), and the characteristics of the most socially important acoustic signal - speech.

Modern hearing aid fitting requires a special room equipped with a soundproof chamber, tone and speech audiometers, devices for presenting sound signals in a free field, testing and computer adjustment of the hearing aid, etc.

As noted by V.I. Pudov (1998), when selecting a hearing aid, in addition to the tonal threshold audiogram, the thresholds of auditory discomfort are measured, the noise immunity of the sound analyzer is examined, the presence of loudness function disorders is identified, and speech audiometry is performed in a free sound field. Usually, the patient is recommended the type of hearing aid that provides the lowest threshold of 50% speech intelligibility, the highest percentage of speech intelligibility with the most comfortable speech perception, the highest threshold of discomfort in speech perception, and the lowest signal-to-noise ratio.

Contraindications to hearing aids are very limited. These include auditory hyperesthesia, which can serve as a trigger for various prosopalgias and migraine conditions, dysfunction of the vestibular apparatus in the acute stage, acute inflammation of the outer and middle ear, exacerbation of chronic purulent inflammation of the middle ear, diseases of the inner ear and auditory nerve, requiring urgent treatment, and some mental illnesses.

The question of binaural hearing aid fitting is decided individually. Monaural fitting is performed on the side of better speech intelligibility with a flatter curve (with less hearing loss at high frequencies), a higher threshold of discomfort speech perception, giving a higher percentage of speech intelligibility at the most comfortable level of its perception with a hearing aid. The design of earmolds (their individual manufacture) plays a significant role in improving the quality of perception of the sound signal.

Primary hearing aid fitting involves a period of adaptation to the hearing aid, which lasts at least one month. After this period, the hearing aid parameters are adjusted as needed. For young children, hearing aids are used that have a maximum output sound pressure level of no more than 110 dB, nonlinear distortion of less than 10 dB, and the hearing aid's own noise of no more than 30 dB. The frequency band of the hearing aid for children who do not speak is chosen to be as wide as possible, since speech training requires complete acoustic information about speech sounds. The frequency band for adults can be limited to limits sufficient for recognizing words.

Surdology is a section of otolaryngology that studies the etiology, pathogenesis and clinical picture of various forms of hearing loss and deafness, developing methods for their diagnosis, treatment, prevention and social rehabilitation of patients. The subject of study of surdology is hearing impairment that occurs as a consequence of inflammatory, toxic, traumatic, professional, congenital and other diseases of the organ of hearing. Deafness is a complete lack of hearing or such a degree of its decrease that speech perception becomes impossible. Absolute deafness is rare. Usually there are "remnants" of hearing that allow the perception of very loud sounds (more than 90 dB), including some sounds of speech pronounced in a loud voice or shouting over the ear. Intelligibility of speech perception in deafness is not achieved even with a loud shout. This is how deafness differs from hearing loss, in which sufficient amplification of sound ensures the possibility of speech communication.

The most important audiological method for studying the prevalence of hearing loss and deafness is screening audiometry among children. According to S. L. Gavrilenko (1986 - the period of the most effective audiological care for children in the USSR), during an examination of 4,577 children aged 4 to 14 years, hearing and auditory tube function disorders were detected in 4.7%, with cochlear neuritis - in 0.85%, adhesive otitis - in 0.55%, chronic purulent otitis media - in 0.28% of children; a total of 292 children.

It is also important to conduct audiological measures in those secondary technical educational institutions where training in "noise" specialties takes place. Thus, according to the data of the Kyiv Research Institute of Otolaryngology named after A.I. Kolomiychenko, reflecting the state of the hearing function in students of vocational and technical schools in the profile of noise professions, they have been diagnosed with an initial form of perceptual hearing loss. Such persons require special audiological monitoring during their further industrial activity, since they constitute a risk group with respect to industrial noise hearing loss.

The means of audiological assistance are various methods of studying the auditory function ("live speech", tuning forks, electroacoustic devices, etc.) and its rehabilitation (medicinal and physical therapy, electroacoustic hearing correction using individual special hearing aids). Directly related to surdology are methods of invasive hearing rehabilitation, including functional otosurgery techniques (myringoplasty, tympanoplasty, fenestration of the ear labyrinth, mobilization of the stapes, stapedoplasty, cochlear implantation). The latter is a combination of surgical intervention with the implantation of an electronic analogue of the SpO receptors.

Modern methods of hearing examination allow to determine with a high degree of accuracy the complete absence or presence of hearing remnants, which is of great practical importance for choosing a method of social rehabilitation of the patient. Significant difficulties arise in recognizing deafness in young children, since the use of conventional methods (speech, tuning fork, electronic-acoustic) does not achieve the goal. In these cases, various methods of "child" audiometry are used, for example, sounding toys and various play audiovisual tests based on visual fixation of spatially separated sound sources or the development of a conditioned reflex to sound when combined with another heteromodal stimulus. In recent years, the registration of evoked auditory potentials, acoustic reflexometry, otoacoustic emission and some other methods of objective examination of the organ of hearing have become widespread for diagnosing hearing disorders in young children.

The occurrence of deafness in adults who can speak leads to the loss of the ability to communicate with others using auditory perception of speech. Various methods of deaf education are used for such patients - lip reading, etc. The consequence of congenital deafness or deafness that arose in the prelingual period, when the child has not yet acquired strong speech skills, is dumbness. In the corresponding social educational institutions (kindergartens and schools for the deaf), such children are taught to understand speech by the movements of the speech-motor apparatus of the interlocutor, to speak, read, write, and the "language" of gestures.

Pathological processes in the nervous structures of the organ of hearing usually lead to persistent disturbances of the auditory function, therefore the treatment of patients with sensorineural deafness and hearing loss is ineffective; only some stabilization of further hearing deterioration or some improvement in speech intelligibility and reduction of tinnitus is possible due to improved trophism of the auditory centers when using drugs that improve microcirculation in the brain, antihypoxants, antioxidants, nootropics, etc. If it occurs as a result of disturbance of the sound conduction function, then surgical methods of hearing rehabilitation are used.

Preventive audiological measures in the fight against deafness include:

1. timely detection of nasopharyngeal diseases, dysfunctions of the auditory tube and their radical treatment;
2. prevention of ear diseases through systematic monitoring of sick children in infectious disease hospitals and healthy children in children's institutions and schools; early and rational treatment of identified diseases;
3. implementation of preventive measures at enterprises with industrial noise, vibration and other occupational hazards that may negatively affect the function of the auditory analyzer; systematic dispensary observation of persons working in conditions of industrial hazards:
4. prevention of infectious diseases, especially rubella, in pregnant women and timely and maximally effective treatment of identified diseases;
5. prevention of drug-induced, in particular antibiotic-induced, ototoxicosis, their timely detection and treatment, for example, by prophylactic administration of the |5-adrenoblocker obzidan during treatment with aminoglycoside antibiotics.

Deaf-muteness (surdomutism) is one of the most common complications of hearing loss in early childhood. With hearing loss in early childhood up to 60 dB, the child's spoken language will be somewhat distorted, in accordance with the degree of hearing loss. With hearing loss in a newborn child and in subsequent years at speech frequencies over 70 dB, the child can practically be identified with a completely deaf child in terms of speech learning. The development of such a child remains normal until 1 year, after which the deaf child does not develop speech. He pronounces only a few syllables, imitating the movements of the mother's lips. At 2-3 years old, the child does not speak, but his facial expressions are highly developed, mental and intellectual disorders appear. The child is withdrawn, distances himself from other children, unsociable, hot-tempered and irritable. Less often, children, on the contrary, are expansive, overly cheerful and active; their attention is attracted to everything around them, but it is unstable and superficial. Children suffering from deaf-muteness are subject to special registration; in relation to them, it is necessary to carry out social rehabilitation measures provided for by special instructions and legislative acts in special kindergartens and educational institutions where they are taught by teachers of the deaf.

Deaf pedagogy is a science of upbringing and educating children with hearing impairments. The objectives of deaf pedagogy are to overcome the consequences of hearing impairment, develop ways to compensate for them in the process of education and upbringing, and form a child as a socially adequate subject of society. The most severe consequence of deafness and severe hearing loss is the obstacle they create for the normal development of speech, and sometimes the child's psyche. The basic sciences for deaf pedagogy are linguistics, psychology, physiology, and medicine, which help to reveal the structure of the disorder, the features of the mental and physical development of children with hearing impairments, the mechanism for compensating for this disorder, and to outline ways to implement it. Domestic deaf pedagogy has created a classification of hearing impairments in children, which forms the basis for a system of differentiated education and upbringing in special institutions for children of nursery, preschool, and school age. Deaf pedagogy is based on the general principles of teaching and educating deaf-mute, deaf and hard-of-hearing children of all ages. There are special curricula, programs, textbooks and manuals, as well as methodological aids for students and practitioners. Deaf pedagogy as an academic discipline is taught at defectology faculties of pedagogical universities and at advanced training courses for deaf teachers.

In the modern conditions of technical progress, audio and video electronic means, including computer programming of electronic hearing rehabilitation means, are acquiring increasing importance for deaf education. The latest developments in computer audiometry, based on the method of recording and analyzing auditory evoked potentials, are of great importance for this problem. New technical means are being developed, such as sound and hearing measuring devices, sound amplifying and sound analyzing devices, devices for transforming sound speech into optical or tactile signals. Individual hearing correction means, which form the basis of hearing aids, are of great importance in the social rehabilitation of hearing-impaired persons of all ages.

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