Audiogram

The audiogram (also known as pure-tone audiometry (RTA ), audiogram, or shortly known as audiogram ) describes the subjective hearing for tones, so the frequency-dependent hearing sensitivity of a human.

It is as a method of audiometry an important diagnostic tool of Oto- Rhino-Laryngology. With an audiogram statements can be made about the symptoms and sometimes about the causes of hearing impairment. Deviations from the norm in audiogram indicate a disease of the ear.

Create an audiogram

For the record a Tonaudiogrammes the cooperation of the subjects is necessary. The examiner plays in turn certain sounds in increasing volume through headphones or bone conduction receiver, for certain questions via speaker. The increase in volume occurs at most Tonaudiometern in 5 - decibel increments. The subject indicates the agreed signal (usually by pressing a button ) as soon as he hears the sound. This process is repeated until the hearing threshold is accurately determined. The investigation is carried out both on air line and via bone conduction. The observed decibel value is entered for each tested frequency as hearing threshold in a standardized form. On the horizontal axis of this form, the pitch (frequency in hertz ) is shown, the vertical axis shows the sound level in decibels, in which the hearing threshold. The title of the unit is dB HL ( Hearing Level as ), since a frequency-dependent related to the normal hearing threshold sound pressure level is given. For the results of uniform characters of the form registered, namely air line right "o " left " x " for bone conduction right ">" and left "<".

For this is the standard for the execution of the standard DIN EN ISO 8253 " Audiometric test methods " before.

Testimony of an audiogram

An audiogram is made of air conduction ( conduction of the sound signals over the outer ear ) and bone conduction ( conduction of the sound signals through the skull bone ). If the threshold of hearing by air conduction normal, then work ossicles, normal sensory cells in the cochlea ( cochlear ) and the auditory nerve. In a sensorineural hearing loss air conduction and bone conduction which lie in the same way at higher decibel levels than in normal hearing. Become tones over the air line bad, but normally perceived through bone conduction, it is a conductive hearing loss. Both forms of hearing loss can be present simultaneously, while the bone conduction, however, the air conduction is lower than normal, even worse, it is called a mixed hearing.

Sound sources for Tonaudiogramme

For the measurement of the air line headphones are used for certain issues speaker ( Freifeldaudiometrie ). The investigation must be to the exclusion of background noise in a sound-proof, anechoic chamber, usually a soundproof booth done.

For the isolated measurement of the function of the inner ear, a bone conduction receiver is used. A bone conduction hearing aid is basically a loudspeaker, which has no diaphragm, so it can not emit sound through the air. It is created on the side of the ear to be tested to the skull ( mastoid ) and so transmits the vibrations to the bone and directly on the inner ear.

Since spreads when measuring with a bone conduction hearing the sound over the whole skull, the opposite ear hears a significant portion of the signal offered. For a different hearing sensitivity of ears the unexamined better hearing ear is for this reason " deafened " with a loud noise of a headphone ( masking ), so that only the other ear can perceive sounds. For very large differences in side the ear must not tested, masking even when tested with headphones.

Reliability of the result

The investigation is dependent on the cooperation of the person examined. People who are overwhelmed by the task ( eg smaller children), so can not be studied. It is also to aggravate a patient possible, so existing symptoms worse presented as they are, or simulate at all. For a rough assessment of the hearing of non-cooperative persons, similar to the newborn, Early auditory evoked potentials are used.

Distinction after, and sequence

There are various types of recording an audiogram. They differ primarily in the sequence in which the subjects, the sound stimuli are presented and how the respondent reacts to it.

The simplest method is to record a tone below the normal hearing threshold and then increase the level until the subject confirms the perception. To eliminate noise, the method for each tone is repeated usually. It can be recorded with this method discreet hearing thresholds for individual frequencies.

Less common, since relatively time consuming is the Békésy - tracking, in which the pitch is continuously increased and the subject can lower or raise the volume by pressing or releasing a button. As with most other methods, he gets only the instruction to press the button at a hearing impression. Since the respondent has no way to keep the level constant, resulting in a characteristic audiogram, close-knit zigzag line that exceeds the actual hearing threshold alternately under and.

Examples

Audiogram, conductive hearing loss

Audiogram, sensorineural hearing loss

Audiogram, mixed hearing

Typical pathological findings in audiometry are:

• When shaped depression of bone conduction threshold curve in the range of 1-4 kHz ( Carhart - sink) at the same time existing conductive hearing loss and normal tympanic membrane, characteristic of otosclerosis,
• Sink in the low and mid frequency range (bass deafness, " Hydropskurve " ) ( sensorineural hearing loss ), characteristic of Meniere's disease,
• High tone loss ( sensorineural hearing loss ), frequent in presbycusis ( age-related hearing ),
• C5 - sink ( sensorineural hearing loss ), characteristic of noise-induced deafness.