Audiometry

Audiometry is a procedure for studying human hearing, the process of determining auditory sensitivity to sound vibrations. Through its implementation, it is possible to determine the so-called “hearing threshold” of the patient. Audiometric studies are carried out by an audiologist – a doctor who specializes in identifying and treating hearing problems. One of the key areas of his activity is the diagnosis of auditory disorders, including using the audiometry procedure. Usually, patients come to an audiologist on a referral from a general practitioner or an otolaryngologist. In some cases, preventive examinations by this doctor are also necessary.

What is audiometry

In a 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 pathologies, the acuity of auditory perception may gradually or dramatically decrease, and in some cases disappear completely. In this study, the concept of the criterion of auditory norm is encountered – it is the level of perception by the patient’s ear of a whisper from a source located at a distance of six meters from him.

The audiometry technique is painless and harmless to the patient, it does not require any special training, it does not always require special devices and devices, which is why it is recommended to be carried out by both adults and children. At the same time, with its help, it is possible to determine violations in the work of any departments of the hearing aid, and regular preventive examinations of such a plan make it possible to identify and prevent hearing loss already in the early stages of the appearance of such a probability. In addition to, in fact, determining the very fact of hearing loss, an audiologist can calculate the degree of such a decrease in the process of audiometry. The procedure must be carried out before the appointment of hearing aids.

After receiving the results of this diagnostic procedure, the doctor can evaluate the performance 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 tympanic membrane through the external auditory canal, for which speakers or headphones are used, and in the second case, the sound source comes into contact with the head, causing vibration of the bone apparatus of the skull, and, in turn, vibrations of the tympanic membrane. The task of stimulating the bones of the skull is performed by special bone oscillators.

Types of audiometry

Depending on how the examination is carried out, what devices and devices are used, there are several main types of audiometry. The simplest and most accessible is audiometry using live speech, without the use of special equipment. Techniques of this type of speech audiometry are mainly used by otolaryngologists, if during the consultation the patient complains of hearing loss, ear congestion. During the examination, the doctor moves away from the patient for a certain distance, after which he begins to pronounce phrases and words at different volumes, from the usual conversational to a whisper. By the way the patient responds, how clearly and accurately he can repeat what he heard, the doctor can already draw certain conclusions. Unfortunately, this technique is not completely reliable, since its results, not least, depend on the level of development of the patient, on his age.

Types of audiometry using technical devices:

• speech – is a method for determining the perception of speech (live or recorded);
• tonal and threshold – explores the patient’s perception of various sounds that are not related to human speech;
• suprathreshold – a technique used in cases of complete hearing loss. With its help, the specialist receives data on the differential threshold of sound perception;
• computer – carried out using special computer systems and programs;
• objective – based on the fixation of unconditioned auditory reflexes;
• pediatric – used as a method of testing hearing in newborn babies and older children.

An audiometer is used to display the obtained data on the subject’s hearing acuity.

Indications for audiometry

In addition to systematic examinations for the prevention of hearing impairment, there are situations when a hearing test is necessary for objective reasons, for example:

• with diseases of the middle and inner ear, especially if the patient himself notes a deterioration in auditory perception;
• due to brain diseases associated with damage to the auditory cortex of the brain;
• when receiving injuries to the ears and head, which led to a decrease in hearing acuity;
• if you suspect the development of occupational hearing loss;
• upon detection of hearing loss of unknown etiology;
• before selecting and installing a hearing aid;
• with infectious diseases of the ear;
• after taking certain groups of antibiotics (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 to the study of the patient’s hearing acuity, the audiologist conducts a preparatory conversation and a survey with him. The doctor finds out when the hearing problems began, whether they affect one or both ears, whether the patient has ringing, pain or discomfort in the ears. The audiologist will also take an interest in whether infectious diseases or ear injuries have been transferred, what is the level of noise at the patient’s workplace, whether other members of his family have hearing problems.

The examination includes a visual examination of the outer ear for visible deformities, as well as an examination of the ear canal and eardrum using an otoscope.

No special preparations are required before audiometry, however, if possible, it is better to exclude being in noisy places (discotheques, concerts, runways) before it, 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 intensities. For example, the volume of a whisper is about 20 dB, the intensity of noisy music can range from 80 to 120 dB, and the volume of a jet engine reaches 140-180 dB. Exposure to sound above 85 dB for several hours may cause temporary hearing loss. Exceeding the threshold of discomfort (more than 112 dB) causes persistent pain, and can also cause hearing loss.

Hertz allows you to fix such a property of a sound wave as frequency, or pitch. Hertz refers to the number of air vibrations per second that affect the eardrum. Bass tone fluctuates in the range of 50-60 Hz. On average, the operating range of a human hearing aid is between 20 and 20000 Hz. The high tone range is above 10000 Hz. Human speech has a frequency of 500 to 3000 Hz.

Speech audiometry procedure

For the procedure, the patient is placed in a soundproof or soundproof room. The sound is fed through the phone’s headphones or through the speaker. In the second case, the subject should be at a distance of approximately 25-30 centimeters from the sound source. Speakers or headphones reproduce a digital recording of the speaker’s speech, or transmit his live speech. The patient voices the words spoken by the announcer into a special microphone.

The diagnostician, hearing the text transmitted to the subject, and analyzing the patient’s answers, changes the sound intensity using a special electronic device – an attenuator, and monitors how the patient perceives the spoken text. Thus, the doctor determines the minimum volume (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 it is necessary to examine each ear separately.

In the event that the announcer speaks the text live into the microphone, he must pay attention to the voltmeter readings in order to establish how loud the speech is being voiced. This method is considered more convenient, since, firstly, it allows establishing 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, recording ensures that the volume of spoken text is more stable. As for whether to use a male or female voice for the examination, judging by the opinions of doctors, no significant difference was found in the results of speech audiometry, depending on the gender of the speaker. 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 were compiled in the form of tables. With their help, you can 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, patients have a greater hearing loss, and in the case when the subject hears a coherent meaningful speech consisting of logically composed sentences, the chance increases that he can guess or think out unheard phrases or words. The best option is to use phrases consisting of two or three logically related words.

For a full-fledged examination of the capabilities of the human hearing aid, such an indicator as the dynamic range of speech perception, which is directly related to the concept of the threshold of unpleasant sensations, is also important. 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 normal level, the range narrows.

There is also a criterion for favorable and unfavorable levels of speech perception. In the first case, the patient can normally perceive speech for a long period of time, and in the second – usually no more than 2-3 minutes. In people with a normal level of hearing acuity, the threshold of perceived loudness is more than 60 dB, and unpleasant sensations are caused by sounds louder than 112 dB. An increase in the threshold of unpleasant sensations by 5-10 dB is observed with damage to the sound-conducting apparatus, and a decrease in some progressive processes, for example, with toxic neuritis.

Tone and threshold audiometry

To determine the limits of the patient’s sound perception, the doctor conducts an examination in the frequency range from 125 to 8000 Hz, and establishes from what values ​​the patient normally hears sounds. This type of study is carried out using an audiometer. This equipment allows the use of sound signals of varying degrees of intensity – from 125 Hz, and then ascending (250, 500, 750 and more Hz), up to frequencies of 8000 Hz. Devices with available frequencies over 10000 Hz are used less frequently. The switching step is 67,5 Hz. This technique allows you to determine the minimum and maximum values ​​- the level of occurrence of an uncomfortable state, while using both pure tones and a narrowly focused noise screen.

The audiometers used in these cases have on-ear headphones, which are two separate air phones, or two in-the-ear phones that are inserted into the auricle. They also include a bone vibrator used to study bone conduction, a microphone and a button designed for the patient. The recording device connected to the audiometer records the results of the examination.

The room intended for the study must be soundproofed. If this requirement is not met, when analyzing the test results, the doctor must take into account that they may be influenced by external noise. However, in-the-ear phones can solve this problem – their use allows you to get the most objective results, eliminate the likelihood of collapse of the external auditory canal, and also reduce the overall natural noise by 30-40 dB. The level of interaural relaxation at the same time increases to 70-100 dB, which significantly increases the comfort of the patient during the examination.

A signal of a specific tone is transmitted to the patient through headphones, and if he hears it, he presses a special button. If the doctor sees that the button is not pressed, he raises the tone until the subject hears him and presses the button. This determines the minimum value. The maximum perception is detected in the same way – when the signal level exceeds the limit of audibility, the patient releases the button. The results of the examination are displayed in the audiogram.

The norm of threshold hearing is a volume of 0 dB. Switching of sound indicators occurs in steps of 5 dB, reaching the level of 110 dB. Deviation from the zero level is allowed no more than 15-20 dB – in this case, the result is considered normal.

suprathreshold audiometry

In cases where the patient is 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 method of suprathreshold research is used. It includes:

• noise research;
• Fowler’s tests and Luscher’s method;
• Langenbeck tests.

Based on the results of this type of audiometry, it is possible to determine whether the pathology is localized in the ear labyrinth, vestibular or auditory nerve cells.

The Luscher method is the most popular today. With its help, the audiologist determines the differential threshold for the perception of the strength of the sound wave (the index of small increases in intensity). Above-threshold audiometry allows you to balance the strength of the signal using the Fowler technique, as well as fix the initial limit of discomfort.

The examination procedure is carried out in the following way: the patient receives a sound signal with a frequency of 40 dB above the hearing threshold into the headphones. In the range between 0,2 and 6 dB, the signal is modulated. Testing begins at a level 20 dB above the hearing threshold, with a gradual increase in sound intensity, with an interval of 4 seconds. In 0,2 seconds, the sound intensity increases by 1 dB, the patient describes his feelings at the same time, and the doctor examines their correctness.

Having brought the indicators to 3-6 dB, the doctor explains the essence of the test to the subject, and returns the signal intensity to 1 dB. If a defect in sound transmission is diagnosed, the patient in the process is able to distinguish about 20% increase in tone intensity.

With diagnosed conductive hearing loss (impaired sound signal transmission along the auditory pathway), the norm is a violation of the conduction of sound waves from the outer ear to the tympanic membrane, while the modulation depth ranges from 1 to 1,5 dB. With cochlear hearing loss (non-infectious damage to the inner ear), the level of recognizable modulation is significantly lower – about 0,4 dB.

Fowler loudness equalization testing is mainly relevant in case of suspected development of acoustic neuroma (benign tumor), or Meniere’s disease (pathology of the inner ear, in which the amount of endolymph in it increases). Most often, it is performed 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 the hearing thresholds of both sides is no more than 40 dB. In this case, a sound is simultaneously fed to each ear, which has a threshold value for a particular hearing aid, after which the signal entering the deaf ear is increased by 10 dB, while selecting such an intensity on the second ear that, according to the patient’s perception, both signals are of the same tone. . Further, the procedure for raising the tone and equalizing the volume in both ears is repeated.

Computer method of hearing research

This method of examination does not require the active participation of the test subject, it can be applied even to newborn children. Computer audiometry is considered the most reliable and informative way to study the possibilities of human hearing, since the objectivity of the data obtained does not depend on the patient or the doctor’s ability to interpret the result. The procedure is performed when the patient falls into a state of sleep. Special electrodes are connected to his head, and sound signals of different frequencies are fed into his 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 hearing aid lesions

This type of hearing test is especially used for newborn babies and young children. The results of objective audiometry are based on the analysis of the reflexes of the human body, which are triggered in response to certain sound stimuli, and are recorded regardless of the actions or desires of the patient.

These reflexes are:

• pupil dilation (cochlear-pupillary reaction);
• closing of the eyelids with unexpected sound exposure (auropalpebral reflex);
• contraction of the circular muscle of the eye;
• in infants – inhibition of sucking reflexes 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 conduction of the body through the skin of the palms.

The most modern methods used for hearing diagnostics are:

1. Acoustic impedancemetry: as a result of its implementation, it is possible to assess the condition of the middle ear. Within the framework of this technique, two procedures are performed – tympanometry and registration of the acoustic reflex. The first type of study gives the doctor the opportunity to diagnose the level of mobility of the tympanic membrane 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 tympanic membrane under conditions of various microfluctuations in the external auditory canal. As for the acoustic reflex, we are talking about the registration of a signal from the intra-ear muscles in response to an impact directed at the eardrum.
2. Electrocochleography is a diagnostic method carried out with artificial electrical stimulation of the auditory nerve. This stimulation causes the cochlea to activate.
3. Electroencephaloaudiometry is a procedure that allows you to fix the evoked potential of the auditory zones of the cerebral cortex (in the process of its implementation, an electroencephalogram is recorded).

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, due to age, contact an audiologist. Such patients are mentally ill people, newborn babies and young children, defendants and prisoners.

Peculiarities of pediatric audiometry

The definition of hearing impairment in a child is a complex problem. This happens mainly because a small child, and even more so a newborn baby, is simply not able to identify a violation in himself and explain the situation to his parents in detail. It is also more difficult to work with children because their attention during the research process is more difficult to maintain, they get tired faster, which can lead to distorted results.

The audiological examination of infants has a well-defined scheme, which is followed by an audiologist. The doctor can carry out the first appointment of a tiny patient already on the 3-4th day of his life. Initially, the doctor performs an external otoscopy – visually assesses the condition of the outer ear and tympanic membrane. Given the specifics of the baby’s age, the possibility of detecting various kinds of contaminants (sulfur, generic lubricant), as well as external deformations or hyperemia, is not ruled out. In such cases, further diagnosis is made no earlier than 2 weeks after the cleaning and treatment of the hearing aid is carried out.

The tympanometry method can be applied to a newborn – an examination of the condition of the tympanic membrane and middle ear using a special probe that reproduces a series of frequencies with certain characteristics. According to its results, it is possible to identify developmental pathologies, as well as the presence of infectious inflammatory diseases.

The next step in the examination of the newborn is the registration and analysis of the induced otoacoustic emission. It is known that in response to a specific sound impact, the human hearing aid is able to generate response impulses. It is on this principle that the specified diagnostic method is built. If deviations and violations were revealed in the process, the child is referred for a consultation with an otolaryngologist and an audiologist.

Older children, for example, school or primary school, can be tested for hearing in a playful way – it’s easier to get them to stay focused and interested in the process for a long time. 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 from those that he already owns at the moment the sound appears. Sound audibility is determined in the range from 250 to 4000 Hz, separately for each ear. Sound signals are given alternately with different frequencies.

The concept of an audiogram, the mechanisms for its decoding

The result of the testing of the hearing aid is an audiogram – indicators converted into a graph. Its horizontal axis displays the frequency of the sound, along the vertical axis – the corresponding hearing threshold, while the vector axis is at the top. The displayed sound wave threshold ranges from 125 to 8000 Hz.

For each ear, a separate audiogram is compiled, which is designated differently: the graph of the right ear is marked as AD, the left – AS. The appearance of the graphs is also different – the audiogram of the right ear is displayed in red, and circles are shown instead of dots. For the left ear, the graph is displayed in blue and 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 – like a dotted line. In this case, the bone conduction line is always located higher than the air line. The distance between them is called the air-bone interval, and normally should not exceed a value of 10 dB.

By reading the graphs, the 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 according to the schedule are:

• conductive (when the air conduction of sounds is disturbed);
• mixed (if both types of sound conduction are disturbed);
• sensorineural (in cases where bone sound conduction repeats air).

The causes of hearing loss in some cases are also displayed on the graph, for example, if the value of the air-bone interval is more than 20 dB, the doctor draws conclusions about the presence of conductive hearing loss, which appears as a result of otosclerosis or otitis media. The value of the graph for the final diagnosis cannot be overestimated. Deciphering an audiogram does not make it possible to draw absolutely accurate conclusions without further research.

Examining the patient, it is important for the doctor to determine the degree of damage and the level of hearing loss. To do this, he pays attention to the location of the graph curve. In patients with mild hearing loss, decibel values ​​are between 20 and 40 dB, with moderate hearing loss, the graph values ​​are between 41 and 55 decibels, with moderately severe hearing loss, between 56 and 70 dB, and severe hearing loss is shown in values ​​between 71 and 90 dB. The readings for each ear may vary. The normal range is from 0 to 25 dB. The graph in the volume above 91 dB indicates absolute deafness.

If the curve tends to go down, this indicates a difficult perception of high frequencies, and vice versa. The hyperbolic curve indicates that the hearing loss is most severe in the middle of the range. In such cases, a person can perceive only very loud sounds. Audiogram indicators are necessary for diagnosing the degree of hearing loss, determining the cause of the impairment, its data are very important for the process of fitting a hearing aid.

Normal Audiometry Results

In the course of the diagnosis, the doctor can conclude that the patient has a normal level of hearing acuity, if he is able to hear the whisper, ticking of the clock, normal speech. This is also evidenced by symmetrical 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 or less.

When analyzing the data obtained, 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 also interested in such a question. When conducting a computer form of testing, it is impossible to deceive the equipment in any way, since it fixes indicators that a person cannot consciously influence. As for speech audiometry, in this case, the subject can simulate hearing loss, pretending not to hear the text spoken by the announcer.

It is almost impossible for a patient to give out indicators of auditory perception higher than they actually are, even in the conditions of speech audiometry.

Audiometry is the main way to examine the condition 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 methods allow obtaining complete and accurate data on the level of the patient’s auditory perception, and, if hearing loss is diagnosed, what caused such a decrease. The information collected through the conduct of an audiogram makes it possible to identify disorders and pathologies, to study their nature, and to determine the direction of their treatment. Audiometry is mandatory if the patient needs to fit a hearing aid.

The procedure is recommended for both children and adults. Preventive hearing screenings are the best way to keep your acuity normal.