Audiometry is a method of determining the sensitivity of the auditory analyzer to sound vibrations of varying intensities. Diagnostic examinations are carried out by an audiologist, who, according to the curves of the audiogram, can determine the hearing threshold of bone- and air-conducted sound signals. The results of the examination make it possible to diagnose hearing loss and the degree of its development in patients with ear pathologies.
During the audiometric examination, the patient is given sound signals of various wavelengths (frequencies) and intensities. According to the patient's subjective sensations, the points of minimum sound are marked on the graph, which are captured by the auditory analyzer. Each of the obtained points on the graph indicates the minimum intensity of a sound vibration of a given frequency. After processing the graph and connecting all the points, the audiologist receives two curves: the minimum threshold for bone and air sound conduction of tones.
Tonal audiometry
What is Hearing Audiometry? Audiometry is a method of determining the minimum sound intensity that can be perceived by the sound-conducting and sound-perceiving parts of the auditory analyzer. In the absence of pathologies, a person is able to hear a whispering speech or the ticking of a clock, the intensity of sound vibrations of which lies in the range from 0 to 25 dB.
The inability to perceive sound vibrations with an intensity below 26 dB indicates hearing impairment.
There are several types of audiometric studies, the main ones of which are:
- computer;
- speech;
- tonal.
Tonal audiometry is a method for determining the degree of hearing loss by the threshold of sound perception with a frequency range from 125 to 8000 Hz. Thanks to the examination, the specialist can determine the minimum level of the patient's hearing sensitivity, which gives grounds for making an accurate diagnosis and determining the degree of development of hearing loss.
Indications
Audiometric tests are one of the most reliable, among other otolaryngological examinations, to assess the threshold of auditory sensitivity. Direct indications for passing an acoustic examination are:
- otosclerosis;
- autophony;
- hearing loss;
- eustachitis;
- recurrent otitis media;
- traumatic brain injury;
- frequent inflammation of the nasopharynx;
- abnormal structure of the organ of hearing.
The procedure has no contraindications and does not require special training. The instrumental examination method allows you to determine the presence of tumors, anatomical abnormalities in the structures of the ear, and obstacles formed during inflammation of the soft tissues. Thus, the ENT doctor determines with high accuracy in which of the parts of the auditory analyzer there are pathological changes leading to the development of auditory dysfunction.
Terminology
To understand how audiogram testing is done, you need to understand the audiometry method and related terminology. Hearing acuity is determined from data that takes into account two main characteristics of sound vibrations:
- frequency (wavelength) - a characteristic of the number of oscillations of sound signals in 1 second, which is expressed in hertz (Hz);
- intensity is a physical quantity that determines the pressure strength of the vibrations created by the sound wave. For convenience, audiometric studies use not a scalar, but a relative value, which is measured in decibels (dB).
Tonal audiometry is a subjective measure of auditory perception that requires feedback from the subject. The audiologist, using an audiometer, gives sound signals of a certain frequency and intensity, while the patient informs him whether he perceives sounds or not. In otolaryngology, it is the tonal method of detecting disturbances in the operation of the auditory analyzer that is most often used, which makes it possible to assess the degree of susceptibility of hair cells and possible disturbances in the sound-conducting and sound-receiving system.
Plotting a graph
Audiometric examinations begin with checking the healthy ear. Using a special earpiece placed on the auricle, the specialist determines the air conduction threshold. To determine bone conductivity on the bone of the mastoid process, located behind the auricle, a special vibrator is fixed.
Air conduction results give an estimate of the patient's threshold of auditory sensitivity, and bone conduction indicates the perception of sound signals when the sound-conducting system is excluded - “cochlear reserve”. The audiogram of the ear allows you to determine with high accuracy in which part of the auditory analyzer there are violations.
In the absence of obstacles on the path of the sound wave through the sound-perceiving system, the vibrations created by it in the bone structures of the inner ear will be amplified many times over. In the presence of pathologies in the middle or outer ear, only vibration will reach the ear labyrinth and, accordingly, the hair cells (receptors).
Audiometry standards
The result of an audiometric examination is an audiogram, which shows 4 signal curves: two for the right and two for the left ear. According to the graphic data, the specialist evaluates the degree of susceptibility of the hair cells, i.e. auditory receptors. According to the international classification, the degree of hearing loss is determined by comparing the results obtained with standard data:
- 26-40 dB - insignificant hearing loss (1 degree of hearing loss), in which the patient has difficulty distinguishing whisper speech;
- 41-55 dB - average hearing loss (2nd degree of hearing loss), in which the patient does not perceive normal speech at a distance of more than 10 m;
- 56-70 dB - severe hearing loss (grade 3 hearing loss), in which the patient is able to perceive high-intensity sound signals;
- 71-90dB - very severe hearing loss (4th degree of hearing loss), in which the patient distinguishes very loud speech delivered at a distance of no more than 40 cm from the auricle.
When diagnosing clinical deafness, patients are not able to perceive sound vibrations with an intensity of more than 120 dB. In the event of complete deafness, hearing-verbal communication with patients is almost impossible.
Interpretation of results
Hearing audiogram is a graphical representation of the results of an audiometric study. In a two-dimensional coordinate system, the horizontal (abscissa axis) indicates the frequency of sound vibrations in Hz, and the vertical (ordinate) indicates the intensity of the sound signal in dB. As a rule, the graph depicts two curves, one of which demonstrates the threshold sensitivity of bone, and the second - air conduction of tones.
Bone conduction indicates the presence of resistance to vibrations created by sound vibrations in the structures of the inner ear and the bones of the skull. Air conduction allows you to diagnose the presence of obstructions in the path of the sound signal through the airways of the middle and outer ear.
How to interpret the results? A normal audiogram contains two graphs, the extreme points of which lie in the range from 0 to 25 dB. In this case, the difference between the graphic results of air and bone conduction of sound is called the bone-air interval. When evaluating the results of the study, the doctor analyzes the following data:
- if the bone conduction curve of sound signals is within the normal range, and the air curve is much lower, this indicates the development of conductive hearing loss;
- if both curves coincide, but at the same time are located below the normal range, sensorineural hearing loss is diagnosed;
- the presence of a large bone-air interval, in which both curves are outside the normal range, indicates the development of mixed hearing loss.
The audiogram for sensorineural hearing loss allows you to determine the threshold perception of sound signals by the size of the bone-air interval. Audiometric diagnostics is one of the most reliable ways to determine the severity of hearing loss.
When diagnosing grade 4 sensorineural hearing loss, the auditory analyzer is not able to perceive and process sounds with an intensity below 91 dB.
Patients with this pathology practically do not distinguish sounds even while using hearing aids.
