Tone Audiometry

Pure-tone audiometry is a non-invasive diagnostic examination widely used in otorhinolaryngology that allows determination of a patient’s hearing threshold at different frequencies of the sound spectrum. The examination is performed using specialized equipment — an audiometer.

The method is based on the presentation of pure tones through headphones (to assess air conduction) and/or through bone vibrators (to assess bone conduction) in order to determine the minimum sound level perceived by the patient.

During air conduction testing, sounds of different frequencies and intensities are delivered through headphones. When the patient hears a sound, they press a button, and the device records the result on a graph — the audiogram. By gradually changing the sound parameters, the device generates a continuous curve representing the air-conduction hearing threshold.

To assess bone conduction, special sensors — bone conduction vibrators — are placed on the mastoid processes behind the patient’s ears. When the vibration is perceived, the patient presses the button. The result is displayed as a dashed curve on the audiogram, reflecting the bone-conduction hearing threshold.

Anatomy of the auditory analyzer

• Outer ear (auricle, ear canal) — captures sound waves;
• Middle ear (tympanic membrane, auditory ossicles) — transmits vibrations;
• Inner ear (cochlea) — converts mechanical vibrations into nerve impulses;
• Auditory nerve — transmits signals to the auditory centers of the brain.

Hearing disorders may occur at any stage — from sound capture by the outer ear to processing in the cerebral cortex. Audiometry allows localization of possible dysfunctions at any level of the auditory analyzer.

Components

• Audiometer — the main device that generates tones of various frequencies and intensities;
• Headphones — used to assess air conduction (function of the outer and middle ear);
• Bone conduction vibrator (tuning-fork–type transducer) — used to assess inner ear function;
• Response button — allows the patient to indicate sound perception.

Audiometry makes it possible to assess both air and bone conduction, as well as the function of both peripheral and central parts of the auditory analyzer.

Results are recorded in the form of an audiogram — a graph in which sound frequency is plotted on the horizontal axis and intensity on the vertical axis.

Purpose of the examination

• Determination of hearing thresholds at each tested frequency (usually from 125 Hz to 8 kHz);
• Diagnosis of the type of hearing loss: conductive, sensorineural, or mixed;
• Monitoring of hearing in chronic diseases, noise exposure, or during the use of ototoxic drugs;
• Selection of hearing aids or treatment planning (including hearing rehabilitation and surgery).

Indications

• Complaints of hearing loss or ear fullness;
• Chronic otitis media, otosclerosis;
• Head or ear trauma;
• Tumors of the brain or ear structures;
• Acute cerebrovascular disorders;
• Hearing screening in newborns, children, and adults;
• Monitoring of hearing during treatment with ototoxic medications;
• Occupational hearing surveillance in noisy work environments.

Pure-tone audiometry is a safe and painless procedure.

Audiometry is not recommended during acute inflammatory diseases of the ear.

Procedure

• Performed in a specialized room or in a soundproof acoustic booth;
• The patient puts on headphones and receives a response button;
• Each ear is examined separately. The specialist presents signals of different frequencies and intensities;
• The patient presses the button when the sound is perceived;
• If necessary, bone-conduction audiometry is also performed;
• Average duration of the examination is 15–30 minutes.

During the examination, mild discomfort in the ear may occur.

The results are displayed as an audiogram reflecting the patient’s hearing thresholds at different frequencies for each ear. Interpretation is performed by an otorhinolaryngologist or an audiologist.

Pure-tone audiometry allows accurate determination of the degree and type of hearing loss and helps establish the need for further examinations or rehabilitation measures.

Sources:

https://emedicine.medscape.com/article/1822962-overview https://www.ncbi.nlm.nih.gov/books/NBK580531/
https://www.asha.org/public/hearing/pure-tone-testing/?srsltid=AfmBOorZoAbh5yZXmv5lM4S8UafmY1gLBah4n__kbfyPf9MFCGdrhqCL
https://vula.uct.ac.za/access/content/group/27b5cb1b-1b65-4280-9437-a9898ddd4c40/Theory%20and%20practice%20of%20pure%20tone%20audiometry%20_PTA_.pdf
https://www.thebsa.org.uk/guidance-and-resources/current-guidance/?subject=adult-audiology