Audiometry is a procedure for the study of human hearing, the process of determining auditory sensitivity to sound vibrations. Through its implementation, it is possible to determine the so-called “threshold of hearing” in a patient. Audiometrical research is carried out by an audiologist who specializes in identifying and treating hearing problems. One of the key areas of its activity is precisely the diagnosis of auditory disorders, including using the audiometry procedure. Patients usually get to the audiologist by referral from a therapist or otolaryngologist. In some cases, preventive examinations are necessary for this doctor.
What is audiometry?
In the normal state, human hearing is able to perceive a fairly wide range of sound vibrations. However, due to various reasons, such as injuries, infectious lesions, congenital abnormalities, the acuity of the auditory perception may gradually or dramatically decrease, and in some cases disappear completely. In this study, the notion of the criterion of the auditory norm is encountered - it is considered the level of perception of a patient's whisper from a source at a distance of six meters from the patient’s ear.
The method of conducting audiometry is painless and harmless to the patient, it does not require any special training, for its implementation it is not always necessary to use special devices and devices, which is why it is recommended for both adults and children. At the same time, it can be used to identify violations in the work of any departments of the hearing aid, and regular preventive examinations of such a plan can detect and prevent hearing loss in the early stages of the appearance of such a probability. Besides, in fact, determining the very fact of hearing loss, the audiologist can calculate the degree of such a decrease in the process of audiometry. The procedure is necessarily carried out before the appointment of hearing aids.
After receiving the results of this diagnostic procedure, the doctor can evaluate the quality of the entire hearing aid using the air conduction method, or study the functionality of the inner ear using the bone conduction method. In the first case, sound waves cause vibrations of the eardrum through the external auditory canal, for which speakers or headphones are used, and in the second, the sound source touches the head, causing vibrations of the skull bone apparatus, and, in turn, vibrations of the eardrum. The task of stimulating the bones of the skull is performed by special bone oscillators.
Types of audiometry
Depending on how the survey is conducted, which devices and devices are used, there are several basic types of audiometry. The most simple and accessible is audiometry using live speech, without the use of special equipment. Receipts of this type of speech audiometry are mainly used by otolaryngologists, if the patient complains of hearing impairment or ear congestion during the consultation. In the course of the examination, the doctor moves away from the patient for some distance, after which he begins to pronounce phrases and words with different loudness, from ordinary conversational to whispering. By the way the patient responds, how clearly and accurately can repeat what he heard, the doctor can already draw certain conclusions. Unfortunately, this technique is not completely reliable, since its results, not least of all, depend on the level of development of the patient, on his age.
Types of audiometry using technical devices:
- speech is a method for determining speech perception (live or recorded);
- tonal and threshold - examines the patient's perception of the patient of various sounds that are not related to human speech;
- overthreshold - a technique used in cases of complete hearing loss. With its help, the specialist obtains data on the differential threshold of sound perception;
- computer - is carried out using special computer systems and programs;
- objective - based on the fixation of unconditioned auditory reflexes;
- pediatric - is used as a method of testing hearing in newborn babies and older children.
An instrument audiometer is used to display the obtained data on the hearing acuity of the subject.
Indications for audiometry
In addition to systematic examinations for the prevention of hearing impairment, there are situations when testing hearing acuity is necessary for objective reasons, for example:
- in diseases of the middle and inner ear, especially if the patient himself notes deterioration of the auditory perception;
- due to brain diseases associated with damage to the auditory cortex;
- upon receipt of injuries to the ears and head, which led to a decrease in hearing acuity;
- if you suspect the development of professional hearing loss;
- when a hearing loss of unknown etiology is detected;
- before selecting and installing a hearing aid;
- in infectious diseases of the ear;
- after taking certain antibiotic groups (Neomycin, Gentamicin), as well as large doses of salicylates;
- to check and evaluate the results of the treatment.
How is the preparation for the procedure
Before proceeding with the examination of the patient’s hearing, the audiologist conducts a preparatory interview and a survey with him. The doctor finds out when hearing problems began, one or both ears they affect, whether the patient has ringing, pain or discomfort in the ears. Also, the audiologist will ask whether infectious diseases or ear injuries have been transferred, what the noise level at the patient’s workplace is, and whether other members of his family have hearing problems.
Inspection includes visual examination of the outer ear for visible deformations, as well as examination of the ear canal and eardrum using an otoscope.
No special measures of preparation before audiometry are required, however, if possible, it is better to exclude staying in noisy places (discos, concerts, runways) before its holding, and also not to listen to music with headphones.
Decibels and hertz
The use of decibels as a unit for determining the loudness of sound vibrations is due to the fact that the human ear is able to perceive sounds in a wide range of intensity. For example, the volume of whispering is about 20 dB, the intensity of noisy music can vary from 80 to 120 dB, and the volume of a jet engine reaches 140-180 dB. Exposure to sounds of more than 85 dB for several hours can cause temporary hearing loss. Exceeding the threshold of discomfort (more than 112 dB) causes persistent pain, and can also cause hearing loss.
Hertz allow you to fix this property of the sound wave as frequency, or pitch. Hertz refers to the amount of air oscillations per second that affect the eardrum.
The bass tone varies in the range of 50-60 Hz. On average, the working range of a human hearing aid is in the range of 20 to 20,000 Hz. The high tone range is above 10,000 Hz. Human speech has a frequency of 500 to 3000 Hz.
The order of speech audiometry
For the implementation of the procedure, the patient is placed in a sound-proofed or soundproof room. The sound is fed through a telephone headset or speaker. In the second case, the subject should be located at a distance of about 25-30 centimeters from the sound source. Speakers or headphones reproduce a digital recording of a speaker’s speech, or transmit its live speech. The patient voices the words spoken by the announcer in a special microphone.
The diagnostician, hearing the text transmitted to the subject, and analyzing the patient's responses, changes the sound intensity with the help of a special electronic device, an attenuator, and monitors how the patient perceives the spoken text. Thus, the doctor determines the minimum loudness (threshold intensity) of speech, at which the subject hears at least 2/3 of the entire text.
Headphones in this method are used, most often, if necessary, study each ear separately.
In the event that the announcer speaks lively into the microphone, he must pay attention to the voltmeter readings in order to establish how loudly the speech is sounded. This method is considered more convenient, because, firstly, it allows to establish closer contact between the doctor and the subject, and secondly, an audiometer without a recording device provided for in the design has a significantly lower cost. At the same time, the recording ensures that the volume of the voiced text is more stable. As for whether to use a male voice for a survey or a female one, judging by the opinions of doctors, there was no significant difference in the results of speech audiometry, depending on the gender of the announcer. But the constancy of the frequency response of the spoken material, as well as the sufficiency of the diversity of the text, plays an important role in the conduct of the study. For example, to determine the auditory perception of the Russian language, through audiometry, special lists of words in the form of tables were made. With their help, it is possible to establish the degree of intelligibility of the Russian language for the subject.
Scientists and audiologists also note that, for example, the use of single isolated words or long meaningful sentences equally negatively affect the results of the survey, making them less objective. When pronouncing single words, a greater decrease in hearing is observed in patients, and in the case where the subject hears coherent meaningful speech consisting of coherent sentences, the chance is increased that he can guess or think through unheard phrases or words. The best option is to use phrases consisting of two or three logically related words.
For a full-fledged survey of the capabilities of the human hearing aid, such an indicator as the dynamic range of speech perception is also important, which is directly related to the concept of the threshold of unpleasant sensations. In the presence of persistent hearing loss, the threshold may increase - in this case, the dynamic range remains unchanged. If the threshold of discomfort remains at the level of the norm, the range is narrowed.
There is also a criterion of favorable and unfavorable level of speech perception. In the first case, the patient can normally perceive speech for a long period of time, and in the second - usually not more than 2-3 minutes. In people with a normal level of hearing acuity, the threshold of perceived volume is more than 60 dB, and discomfort is caused by sounds louder than 112 dB. An increase in the threshold of unpleasant sensations by 5-10 dB is observed when a sound-conducting apparatus is affected, and a decrease is observed with some progressive processes, for example, with toxic neuritis.
Tonal and threshold audiometry
To determine the limits of the patient's perception, the doctor examines the frequency interval from 125 to 8000 Hz, and determines from what values the patient normally hears sounds. This type of research is carried out using an audiometer. This equipment allows the use of sound signals of varying degrees of intensity - from 125 Hz, and further along (250, 500, 750 and more Hz), up to frequencies of 8000 Hz. Less commonly used devices with available frequencies of more than 10,000 Hz. The switching step is 67.5 Hz. This technique allows you to determine the minimum and maximum value - the level of occurrence of the discomfort state, while applying both pure tones and a narrowly directed noise curtain.
The audiometers used in these cases have overhead headphones, which are two separate air phones, or two ear phones that are inserted into the auricle. Also in their configuration provides a bone vibrator used to study bone conduction, a microphone and a button designed for the patient. A recording device connected to an audiometer records the results of the examination.
The room intended for the study should be soundproofed. If this requirement is not met, the doctor should take into account that external noises may influence them when analyzing test results. However, intra-ear phones are capable of solving this problem - their use allows to obtain the most objective results, exclude the likelihood of a collapse of the external auditory canal, and also reduce the overall natural noise by 30–40 dB. The level of interstitial relaxation at the same time increases to 70-100 dB, which significantly increases the patient's comfort during the examination.
Through the headphones, a signal of a specific key is transmitted to the patient’s ears, and in case he hears it, he presses a special button. If the doctor sees that the button is not pressed, he raises the tone to the rate when the subject hears it and presses the button. This determines the minimum value. The maximum perception is detected in the same way - when the signal level exceeds the hearing limit, the patient releases the button. Examination results are displayed in the audiogram.
The normal threshold for audibility is a volume of 0 dB. Switching sound indicators occurs in 5 dB steps, reaching 110 dB. Deviation from the zero level is allowed no more than 15-20 dB - in this case, the result is considered normal.
In cases where a patient has been diagnosed with deafness, it will be quite difficult for the doctor to accurately determine the location and cause of the lesion. For these purposes, the above-threshold study method is used. This includes:
- noise studies;
- Fowler tests and Luscher method;
- Langenbek tests.
Based on the results of this type of audiometry, it is possible to determine whether the pathology is localized in the ear labyrinth, the cells of the prelum or auditory nerve.
Luscher method is the most popular today. With its help, the audiologist determines the differential threshold of perception of the power of a sound wave (index of small intensity gains). Above-threshold audiometry allows you to balance the strength of the sound signal using the Fowler technique, as well as fix the initial limit of discomfort.
The examination procedure is carried out in the following way: a sound signal is transmitted to the patient’s headset with a frequency of 40 dB above the hearing threshold. In the range between 0.2 and 6 dB, the signal is modulated. Testing begins at a level of 20 dB above the hearing threshold, with a gradual increase in sound intensity, at intervals of 4 seconds. In 0.2 seconds, the sound intensity increases by 1 dB, the patient describes his sensations and the doctor examines their correctness.
Bringing the indicators up to 3-6 dB, the doctor explains to the subject the essence of the test, and returns the signal intensity to 1 dB.If a sound permeability defect is diagnosed, the patient is able to distinguish about a 20% increase in tone intensity in the process.
When diagnosed conductive hearing loss (violation of the passage of the audio signal through the auditory path), the norm is a violation of the conductivity of sound waves from the outer ear to the eardrum, and the modulation depth ranges from 1 to 1.5 dB. With cochlear hearing loss (non-infectious lesion of the inner ear), the level of recognizable modulation is significantly lower - about 0.4 dB.
Testing the loudness alignment according to Fowler is mainly relevant if you suspect the development of an acoustic neuroma (benign tumor), or Meniere's disease (pathology of the inner ear, in which the amount of the endolymph increases in it). Most often it is carried out if unilateral hearing loss is suspected, however, this is not a mandatory rule. With bilateral hearing loss, it is possible to use this above-threshold method, if the difference in hearing thresholds of both sides is no more than 40 dB. In this case, each ear is simultaneously given a sound that has a threshold value for a specific hearing aid, after which the signal entering the deaf ear is increased by 10 dB, while selecting the intensity on the second ear so that according to the patient's perception both signals are of the same tonality . Further, the procedure of raising the pitch and leveling the volume on both ears is repeated.
Computer methods of hearing
This method of examination does not require the active participation of the test subject, it can be applied even to newborns. Computer audiometry is considered the most reliable and informative way to study the possibilities of human hearing, since neither the patient nor the doctor's ability to interpret the result, the objectivity of the data obtained does not depend on. The procedure is performed when the patient is in a state of sleep. Special electrodes are connected to his head, and sound signals of different frequencies are fed into the ear with the help of headphones. A computer program captures the reactions of the brain, and builds an audiogram based on them.
Objective audiometry to detect lesions of the hearing aid
Especially often this method of hearing examination is used for newborns and small children. The results of objective audiometry are based on analyzing the reflexes of the human body, which are triggered in response to certain sound stimuli, and are recorded regardless of the patient’s actions or desires.
These reflexes are:
- pupil dilation (cochlear-pupillary reaction);
- closing the eyelids with an unexpected sound effect (auropalpebral reflex);
- reduction of the circular muscles of the eye;
- in infants, inhibition of the sucking reflex as a reaction to a different tone of the sound signal;
- reactions of the vascular system, for example, the degree of vasoconstriction;
- galvanic skin response, which is measured as the electrical conductivity of the body through the skin of the palms.
The most modern methods used to diagnose hearing are:
- Acoustic impedancemetry: as a result of its implementation, it is possible to assess the condition of the middle ear. In the framework of this technique, two procedures are carried out - tympanometry and registration of the acoustic reflex. The first type of study allows the doctor to diagnose the level of mobility of the eardrum and the chain of the bone component of the hearing aid, allows you to determine the degree of resistance of the air cushion in the cavity of the eardrum under conditions of different microvibrations in the external auditory canal. As for the acoustic reflex, we are talking about registering a signal from the intra-articular muscles in response to an impact directed to the eardrum.
- Electrocochleography is a diagnostic method carried out with artificial electrical stimulation of the auditory nerve. Such stimulation causes snail activation.
- Electroencephalaudiometry is a procedure that allows you to record the evoked potential of the auditory areas of the cerebral cortex (an electroencephalogram is recorded during the process).
The known effectiveness of this type of examinations is that they can be carried out in relation to those patients who do not want, or cannot, for example, by virtue of age, contact the doctor-audiologist. Such patients are mentally ill people, newborn babies and small children, accused and imprisoned.
Features of pediatric audiometry
Determining the hearing impairment of a child is a complex problem. This happens mainly because a small child, and, especially, a newborn baby, is simply unable to identify the violation and explain the situation to the parents in detail. It is more difficult to work with children because their attention is harder to keep in the process of research, they get tired more quickly, because of which the performance can be distorted.
An audiological examination of infants has a well-defined pattern, which the audiologist follows. The doctor can give the first intake of a tiny patient as early as 3-4 days of his life. Initially, the doctor performs external otoscopy - visually evaluates the condition of the outer ear and eardrum. Given the specifics of the age of the baby, the possibility of detecting various kinds of contaminants (sulfur, generic lubricant), as well as external deformations or hyperemia is not excluded. In such cases, further diagnosis is made not earlier than 2 weeks after the cleaning and treatment of the hearing aid is performed.
The method of tympanometry can be applied to the newborn - examining the state of the eardrum and middle ear with a special probe that reproduces a series of frequencies with certain characteristics. According to its results, pathologies of development can be identified, as well as the presence of infectious inflammatory diseases.
The next stage of the examination of the newborn is the registration and analysis of the caused otoacoustic emission. It is known that in response to a specific sound effect, the human hearing aid is capable of generating response pulses. It is on this principle that this diagnostic method is built. If in the process deviations and violations were identified, the child is sent for consultation to the otolaryngologist and audiologist.
Older children, for example, school or primary school, can be tested for hearing in a playful way - it is easier to get them to prolong their concentration and interest in the process. The method is based on the possibility of developing a conditioned motor reflex as a reaction to a certain sound stimulus. The child is invited to perform a specific movement of those he already owns, at the time of the sound. Audible audibility is determined in the range from 250 to 4000 Hz, separately for each ear. Audible signals are alternated with different frequencies.
The concept of an audiogram, its decryption mechanisms
The result of the conducted testing of the hearing aid is an audiogram — indicators converted into a graph. On its horizontal axis, the frequency of the sound is displayed, on the vertical - the corresponding threshold of audibility, with the axis of the vector at the top. The displayed threshold of sound waves is in the range from 125 to 8000 Hz.
A separate audiogram is drawn up for each ear, which is indicated differently: the graph of the right ear is marked as AD, the left ear - AS. The appearance of the graphs is also different - the audiogram of the right ear is displayed with the help of red, and instead of the dots there are circles on it. For the left ear, the graph is displayed in blue and with crosses instead of dots.
The graphs show the level of air and bone conduction: in the first case, the graph looks like a solid line, in the second - as a dotted line. At the same time the line of bone conduction is always located higher than the line of air. The distance between them is called the bone-air interval, and normally should not exceed a value of 10 dB.
Reading the charts, the doctor-audiologist has the ability to diagnose hearing loss, its degree, as well as the presence and nature of other disorders. The most common types of hearing loss that a doctor can determine on a schedule are:
- conductive (when air conduction of sounds is disturbed);
- mixed (if both types of sound conduction are violated);
- sensoronevral (in cases where bone conduction repeats air).
The causes of hearing loss in some cases are also displayed on the graph, for example, when the value of the bone-air interval is more than 20 dB, the doctor makes conclusions about the presence of conductive hearing loss, which occurs as a result of otosclerosis or otitis. It is impossible to overestimate the value of the schedule for the final diagnosis. Decoding an audiogram does not make it possible to draw absolutely accurate conclusions without conducting further research.
When examining a patient, it is important for the doctor to determine the degree of damage and the level of hearing impairment. For this, he draws attention to the location of the curve of the graph. In patients with a mild form of hearing loss, the decibel values are between 20 and 40 dB, with moderate hearing loss, the graph is between 41 and 55 dB, with moderately severe - from 56 to 70 dB, and severe hearing loss is depicted in values between 71 and 90 dB. Indicators for each ear may vary. The normal range is from 0 to 25 dB. The graph in volume above 91 dB indicates absolute deafness.
If the curve is downward, it indicates a difficult perception of high frequencies, and vice versa. A hyperbola-shaped curve indicates that the hearing loss is strongest in the middle of the range. In such cases, a person can only perceive very loud sounds. The audiogram indicators are necessary for diagnosing the degree of hearing loss, determining the cause of the violation, its data are very important for the hearing aid selection process.
Normal indicators of audiometry results
In the process of diagnosis, the doctor can conclude that the patient has a normal level of hearing acuity if he is able to hear the whisper, the ticking of the clock, the normal speech. This is also evidenced by the symmetric normal air and bone conduction of sound. In this case, the patient perceives sound frequencies from 250 to 8000 Hz at a volume of 25 dB and below.
When analyzing the data, the doctor draws attention to some factors that may affect the results of audiometry, for example, the presence of occupational hearing loss, Meniere's disease, otosclerosis, perforation, or rupture of the eardrum.
Is it possible to falsify the results of audiometry?
In some cases, patients are interested in such a question. When conducting a computerized form of testing, it is impossible to deceive the equipment in any way, since it records indicators that a person cannot consciously influence. As for speech audiometry, in this case, the subject may simulate hearing loss, pretending not to hear the text spoken by the speaker.
It is practically impossible for the patient to give out the indicators of hearing perception higher than they are in fact, even in the conditions of speech audiometry.
Audiometry is the main method of examining the state and functionality of the human hearing aid. To establish the final diagnosis, doctors often prescribe a comprehensive audiometric study, which includes several types of audiometry - speech, threshold, computer and objective. All these techniques allow to obtain complete and accurate data on the level at which the patient’s auditory perception is located, and, if a hearing loss is diagnosed, what caused such a decline. The information collected through an audiogram makes it possible to identify abnormalities and pathologies, study their nature, determine the direction of their treatment. Audiometry is required if the patient needs to pick up a hearing aid.
The procedure is recommended for both children and adults. Preventive hearing tests are the best way to keep your sharpness normal.