Introduction
An audiogram is a graph result from an audiometry hearing test. An audiometer is an electronic instrument that creates a series of tones played through headphones. The audiogram helps visualize the audiometer test results displaying the hearing threshold of a person for various frequencies.
A person can look at an audiogram to understand their hearing ability. The chart or graph will show the results from the quietest level that a person can hear and low pitches. The audiogram helps diagnose hearing loss and indicates the type of hearing loss.
What Is Audiometry?
Audiometry is an essential tool that helps assess hearing thresholds in patients with hearing loss. The audiometry results are displayed on an audiogram, which helps visualize and quantify the type of hearing loss. Sounds vary in the loudness and speed of sound wave vibrations or tones. Hearing occurs when sound waves enter the ear and stimulate the nerves of the inner ear. Sound waves travel to the inner ear through the ear canal, eardrum, and middle ear bones and then to the inner ear. After that, the sound travels along the nerve pathways to the brain. Moreover, various causative factors of hearing loss may demonstrate the characteristic patterns on the audiogram, making this testing tool critical for diagnostic purposes.
How Is Sound Measured?
The strength of the sound is measured in decibels (dB). Hearing a sound greater than 85 dB can cause hearing loss after a few hours. Therefore louder sounds can lead to pain and hearing loss in a shorter duration.
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A whisper is considered to be 20 dB.
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Loud music, such as in concerts or festivals, is around 80 to 120 dB.
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The sound of a jet engine is around 140 to 180 dB.
The tone of the sound is measured in cycles per second (cps) or Hertz (Hz). The normal range of human being hearing is about 20 to 20,000 Hz, and some animals can hear up to 50,000 Hz.
The low bass tones range from around 50 to 60 Hz. The high-pitched tones range from 10,000 or higher. Human speech is usually around 500 to 3000 Hz.
How Is This Test Performed?
The healthcare provider may test the hearing by conducting simple tests in the office, such as listening to whispered voices, tuning forks, or examining the ear with an otoscope. Some of the tests that help determine the exact measure of hearing include -
1. Pure Tone Testing (Audiogram) - In this test, the patient is asked to wear specially calibrated headphones and a bone conductor (which vibrates the sounds through the skull). Then pure tones of a specific frequency and volume are administered to one ear at a time. The patient is asked to signal the healthcare professional when they hear a sound. The lowest volume required to hear each tone is displayed on the graph.
When recording the lowest or softest sound wearing headphones, the threshold is called air conduction, and recording the softest sound wearing a bone conductor, the threshold is known as bone conduction. Therefore determining the threshold helps in evaluating the intensity and tones that can be heard by the patient. Moreover, this will also help in determining the amplification needed in the hearing aid in case of hearing loss.
2. Speech Audiometry - This test helps detect the ability to repeat spoken words at different volumes through the headset placed on the ears of the patient.
3. Immittance Audiometry - This test helps in evaluating the functioning of the eardrum and the flow of sound through the ear. For this test, a probe is inserted in the ear, and the air is pumped to change the pressure in the ear as tones are produced. A microphone helps monitor how well the sound is conducted in the ear under different pressures.
4. Tympanometry - This test measures the vibration of the eardrum and middle ear pressure.
What Is an Audiogram Graph?
The audiogram is a graph based on pure-tone audiometry test results, showing the hearing level at different frequencies. It is similar to a graph with y and x-axis, and the results are recorded on the audiogram using red Os for the right ear and blue Xs for the left ear.
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The Y-axis (vertical) measures the loudness or intensity of sound, measured in decibels (dB), and ranges from -10 to 110 on the audiogram.
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The X-axis (horizontal) measures the pitch or frequency of sound, ranges from 125 to 8,000, and is measured in hertz (Hz).
The audiometer can measure the sound conduction in different parts of the ear and helps in determining the type of hearing loss, which includes -
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Conductive Hearing Loss - A hearing loss occurs in the external or middle ear as the sound cannot get past the external or middle ear.
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Sensorineural Hearing Loss - A type of permanent loss of hearing due to damage to the inner ear or nerves responsible for hearing.
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Mixed Hearing Loss - Hearing loss in which both conductive and sensorineural hearing loss occur together.
What Do Audiogram Results Mean?
An audiogram shows various numbers that represent the frequencies and intensities of the sound. The frequencies are arranged horizontally from left to right, ranging from low (125 Hz) to high pitch (8000 Hz). Volume is represented vertically, and from top to bottom, it ranges from very soft (0 dB) to very loud (120 dB).
Below are the symbols a person can see on an audiogram -
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O (Can Be Colored Red) - Result from the right ear measured with headphones (air conduction).
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X (Can Be Colored Blue) - Result from the left ear measured with headphones (air conduction).
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< (Can Be Colored Red) - Result from right ear measured with bone conduction (unmasked).
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> (Can Be Colored Blue) - Result from left ear measured with bone conduction (masked).
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[ (Can Be Colored Red) - Result from right ear measured with bone conduction (masked).
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] (Can Be Colored Blue) - Result from left ear measured with bone conduction (masked).
Masking means the doctor puts some noise in the opposite ear while testing the other ear. This is done to prevent sound from the testing side from going to the other non-testing or normal side. This is called a cross-over problem.
What Are the Degrees of Hearing Loss Based on the Tests?
The hearing test results help identify the level or degree of hearing loss which involves -
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Normal Hearing (0 to 25 dB) - At this level, hearing is within normal limits.
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Mild Hearing Loss (26 to 40 dB) - This may cause difficulty in suppressing background noise and require more effort to listen. Patients with this amount of hearing loss may not hear soft speech. In addition, children may be fatigued after listening for long periods.
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Moderate Hearing Loss (41 to 55 dB) - This may affect language development, peer interaction, and self-esteem. In addition, patients with this degree of loss have trouble hearing some conversational speech.
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Moderate-severe Hearing Loss (56 to 70 dB) - This may cause speech difficulty and decreased intelligence. Patients with this level of loss do not hear most conversational-level speech.
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Severe Hearing Loss (71 to 90 dB) - May affect voice quality.
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Profound Hearing Loss (>90 dB) - Complete hearing loss or deafness, speech and language deterioration.
How to Read the Results?
Some of the following predictions can be made by looking at the audiogram, such as -
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A steady line connecting the threshold levels at the top of the graph will indicate normal hearing.
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A line with ups and downs in the graph indicates hearing loss for particular frequencies.
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A line that goes down from higher frequencies can be seen commonly in aging-related hearing loss.
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A line lower in the graph indicates severe hearing loss.
Normal hearing usually comes between -10 to 15 decibels for every threshold. A person might feel hearing loss between 16 to 25 decibels, but this may not require any treatment.
Conclusion
An audiogram is an important part of hearing tests as it helps in evaluating the hearing capabilities of a person and possible hearing loss. In addition, with the help of an audiogram, it is possible to determine the appropriate approach and treatment for a patient with hearing problems.
