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According to the World Health Organization, about 5% of the world’s population suffers from hearing loss or hearing loss. This number includes 30% of people over the age of 65. Hearing loss (decreased) may be due to congenital causes (intrauterine infections, malformations, aggravated heredity, pathological pregnancy and childbirth, severe neonatal period) or acquired (suspended otitis media, head injuries, infections, taking ototoxic drugs, strong noise or sound exposure , aging).
There are conductive hearing loss, which is caused by damage to the anatomical structures of the outer or middle ear, and neurosensory, which is caused by pathology of the structure of the inner ear or damage to the eighth pair of cranial nerves. To determine the cause and degree of hearing loss in otorhinolaryngology, audiometry is used. This diagnostic method is carried out using an audiometer – an electro-acoustic medical device that captures sound vibrations on a special graph (audiogram).
Types of audiometry
Audiometry is subjective (requires the participation of the patient in the procedure) and objective (does not require the participation of the patient). Subjective audiometry is performed only for those patients who are able to respond to audible sounds as required by the diagnostic technique. Subjective methods include tone and speech audiometry.
Objective diagnostics is carried out in order to establish the degree of hearing loss in young children and in the order of a forensic or labor examination, when there is a possibility of deliberate distortion of the real results of the study. Objective audiometry is also carried out for people suffering from mental disorders. In this case, the study is carried out together with electroencephalography.
Types of audiometers
For audiometry, one of three types of audiometers can be used: screening, polyclinic and clinical. Each of the devices has its own advantages and disadvantages, as well as a list of indicators that can be determined using it.
Screening apparatus
The simplest of them is a screening device, which is designed to examine a large number of people, for example, in “noisy” industries, in the emergency departments of ENT, during medical examinations. The screening audiometer is a tone audiometer: it performs pure tone air conduction audiometry without differential diagnosis of hearing loss. It determines the thresholds of audibility and discomfort. A modern device can be connected to a personal computer or printer to print an audiogram.
More information about the degree of hearing loss is given by a polyclinic audiometer. With the help of this apparatus, it is possible to determine the thresholds of hearing, the perception of sound intensity and speech intelligibility, the decay of tone, the Fowler test. This device is used in diagnostic rooms of polyclinics, ENT departments, specialized centers.
Polyclinic and clinical devices
The polyclinic audiometer (АА-02, AD226) is automated and is designed to assess hearing by setting hearing thresholds for bone and air sound conduction. Clinical devices (AC-40, AC-33) have the maximum possible range of emitted tones and advanced capabilities for various hearing tests. Modern devices are equipped not only with a fixing device, but also with liquid crystal monitors that facilitate the procedure. The results of the study are stored in the memory of the device or in a computer to which the devices are connected using a USB cable.
The principle of operation of devices
The principle of operation of a tone audiometer is to determine the threshold of audibility of sinusoidal tones in the range of 125-8000 Hz. To determine the degree of hearing loss, an audiogram obtained on an audiometer is compared with a zero threshold. In the course of the study, it is determined from the tone of which frequency a person begins to hear the sound. A tone audiometer is built on the patient’s subjective feelings, therefore, it cannot be used for an objective (independent of the subject) assessment of hearing impairment, for example, when conducting a disability examination.
The most modern is a computer audiometer, which provides informative and reliable results of the study of auditory function. They are usually represented by combined devices. The combined audiometer combines the functions of tone and speech instruments. It is used for the differential diagnosis of different types of hearing loss.
To conduct a thorough differential diagnosis of the causes of hearing loss, other examination methods can be used: impendansometry, a hearing test using ultrasound, an SRMS test (auditory response in the brain stem), and others.
Indications and contraindications
The indications for an audiometry procedure are:
- inflammatory diseases of the middle ear;
- hearing impairment;
- hearing loss;
- pain syndrome;
- otosclerosis;
- condition after ear injuries;
- monitoring the effectiveness of treatment;
- selection of hearing aids.
Employees of enterprises and / or workshops where one of the harmful production factors is noise or loud sound are subjected to a mass examination on an audiometer.
Audiometry is a painless and non-invasive procedure, so there are no contraindications to its implementation.
Audiometry indicators
With the help of audiometers, audiometric indicators are evaluated, which include air and bone conduction.
Air conduction
This indicator determines how the patient perceives the sound transmitted through the air. A decrease in air conduction is determined if a person has a defect in the external auditory canal, structures of the middle ear, damage to the auditory nerves.
Bone conduction
This indicator determines how vibration is transmitted through the bones of the skull. To do this, the vibrator of the audiometer is placed on the head of the subject. The vibration is transmitted along the periosteum and reaches the bony cochlea in the inner ear. In this way, the inner ear is directly stimulated. This study excludes the participation of the structures of the outer and middle ear in the formation of sound. Comparison of the results of measurements of air and bone conduction allows for differential diagnosis of the level of damage to the hearing aid.
If, when determining air conduction, the hearing threshold is increased, but it is preserved during bone conduction, then the hearing loss is considered conductive, that is, associated with the pathology of the outer and / or middle ear. With an increase in hearing thresholds, hearing loss is considered neurosensory.
Almost every modern audiometer is equipped with a generator of narrow- and broadband sound waves. When carrying out the determination of air conduction on one ear, the second ear is covered with an earpiece, into which noise is fed, which plays the role of masking. When examining bone conduction, a “bone phone” (vibrator) is used.
Tonal threshold audiometry is used to establish hearing thresholds for tones of frequencies from 125 to 10 thousand Hz. Above-threshold audiometry evaluates the ability of the ear to perceive and interpret sound vibrations of above-threshold strength (extremely quiet or very loud). Audiometers are also used during speech audiometry, during which a person’s ability to recognize human speech is established.
The medical equipment market offers a wide range of audiometers designed for examinations of different levels of complexity. The cost of devices depends on the company and the country of manufacture, the functionality of the equipment and additional options of the device.