Audiogram

Audio23

Typical audiometric "noise notch"

Audiogram is a graphical representation of an individual's hearing ability. It is a key tool used by audiologists and other hearing professionals to assess and diagnose hearing loss. The audiogram plots the threshold of hearing sensitivity across various frequencies measured in Hertz (Hz) against the intensity measured in decibels (dB). This article provides an overview of the audiogram, including its purpose, how it is conducted, and its significance in diagnosing hearing conditions.

Overview

An audiogram is typically obtained through a process called pure-tone audiometry, which involves the individual listening to a range of beeps and whistles (pure tones) through headphones. The tones vary in pitch (frequency) and loudness (intensity). The lowest intensity (volume) at which a person can hear the tone at least 50% of the time is recorded as their threshold for that frequency. These thresholds are then plotted on the audiogram chart, creating a visual representation of the person's hearing ability across different frequencies.

Understanding the Audiogram

The horizontal axis of the audiogram represents frequency, measured in Hertz (Hz), ranging from low frequencies (250 Hz) to high frequencies (8000 Hz), which mimic the range of human speech. The vertical axis represents intensity, measured in decibels (dB), with the numbers increasing from top to bottom. This means that sounds at the top of the chart are softer, while those at the bottom are louder.

Symbols are used to differentiate between the ears; for example, an "O" might represent the right ear, and an "X" the left ear. Additional symbols may be used to indicate responses to sounds presented in ways other than through headphones, such as bone conduction.

Types of Hearing Loss Identified

The audiogram can help identify the type and degree of hearing loss. The type of hearing loss is determined by the configuration of the thresholds plotted on the audiogram and can be categorized as:

• Sensorineural hearing loss: Indicates damage to the inner ear or auditory nerve, characterized by a similar degree of loss across both air and bone conduction.
• Conductive hearing loss: Occurs when sound waves are not efficiently conducted through the outer ear canal to the eardrum and the tiny bones (ossicles) of the middle ear, often showing a gap between air and bone conduction thresholds.
• Mixed hearing loss: A combination of sensorineural and conductive hearing loss, showing aspects of both types on the audiogram.

Degree of Hearing Loss

The degree of hearing loss refers to the severity of the loss and is determined by the range of decibels at which hearing thresholds are recorded:

• Normal hearing: -10 to 20 dB
• Mild hearing loss: 21 to 40 dB
• Moderate hearing loss: 41 to 55 dB
• Moderately severe hearing loss: 56 to 70 dB
• Severe hearing loss: 71 to 90 dB
• Profound hearing loss: 91 dB or more

Clinical Significance

Audiograms are crucial for diagnosing hearing loss, planning treatment, and fitting hearing aids. They help in determining the most appropriate type of hearing aid, setting hearing aid levels, and evaluating hearing aid effectiveness. Audiograms also play a significant role in monitoring hearing loss progression over time.

Conclusion

The audiogram is a fundamental tool in the field of audiology that provides a visual representation of an individual's hearing ability. It is essential for diagnosing the type and degree of hearing loss, guiding treatment decisions, and improving the quality of life for those with hearing impairments.