FUNDAMENTALS OF THE AUDIOGRAM

Whether it’s time for your annual hearing test or you are having an evaluation for the first time, it is important to be educated and proactive in your hearing health.  The purpose of the hearing test is to determine if there is a hearing loss, the severity of the loss and the course of treatment.  The audiologist conducts a series of tests designed to measure your hearing acuity.  An audiometer is the equipment used to measure responses and those responses will be recorded on an audiogram form. The audiogram is a graph of your hearing that allows us to visualize the results of the hearing test across the entire frequency range.

The audiologist will often refer to the audiogram when discussing test results.   The information presented can be overwhelming.   Preparing one’s self with basic knowledge of the audiogram can help you to understand what you can and cannot hear and why you may hear better in certain situations than others.

THE AUDIOGRAM GRAPH:

The audiogram graph shown below illustrates the type, degree and configuration of hearing loss.  Measurement of hearing consists of two parameters:  frequency (pitch) and intensity (loudness).  The numbers across the top of the graph represent the frequencies tested measured in Hertz (Hz).  The range of human hearing is  20-20,000 Hz, however, the audiogram is used to only record frequencies from 250-8000 Hz as these are the frequencies most necessary for the detection and understanding of human speech.  It can be helpful when considering frequency or pitch to think of the keys on a piano keyboard.  Keys on the left of the keyboard are low, base sounds and as we move to the right of the keyboard the scale becomes more higher pitched with treble sounds.  The same principle applies with the audiogram with the low frequencies starting at the left of the graph, moving to higher pitches as we move along to the right. Low frequency sounds include environmental sounds such as ocean waves and higher frequency sounds include birds chirping or certain musical instruments like a piccolo.  The lower pitch sounds are responsible for the power or volume of speech and include the vowel sounds while the higher pitch sounds are our consonants that provide clarity of speech.  Knowledge of this can help explain why you hear better in certain situations over others.

The numbers down the left side of the audiogram represent intensity or loudness of sounds and range from -10 dB to 110 dB with the softer sounds at the top and louder sounds near the bottom. Decibel (dB) is the  unit  of measurement for intensity.

The audiogram is used to plot the pattern (configuration) and the degree of hearing loss.    Pure tone audiometry is the test method used to present tones of different frequencies and intensity levels.  We determine the softest level you can detect at each frequency.  This level is referred to as threshold. Threshold for each frequency is plotted on the audiogram.

HEARING TEST STIMULUS:

Pure tone audiometry is tested two ways: air conduction and bone conduction.  Air conduction audiometry involves the use of headphones or insert phones and the sound is transmitted through the outer ear, middle ear and  inner ear.   Air conduction thresholds are represented as O’s and X’s on the audiogram.  Red O’s represent the right ear and blue X’s represent the left ear.

Bone conduction audiometry utilizes placement of a vibrating device (transducer) on the patient’s mastoid bone behind the ear allowing us to bypass the outer and middle ear and stimulate the inner ear directly.  Bone conduction results are indicated by arrows or brackets on the audiogram.

All air and bone conduction testing is performed in a sound treated room. Once all the frequencies have been tested, the hearing can be described in terms of its type, degree and shape or configuration.

TYPE OF HEARING LOSS:

Hearing loss is categorized as three types: conductive, sensorineural or mixed.  A conductive hearing loss involves the outer and/or middle ear meaning there is some type of barrier such as wax or possibly a foreign object that is impeding the transmission of sound to the inner ear.  A sensorineural loss indicates that the loss has affected the inner ear and is permanent.  Mixed is simply a combination of the two.  In conductive and/or mixed loss there will be a significant difference between the air conduction and bone conduction results. With sensorineural loss the bone conduction results will be equal to the air conduction thresholds.

DEGREE OF HEARING LOSS:

Thresholds measured between 0 and 20dB are considered to be within normal range.  As we examine the audiogram any sounds that fall below the persons thresholds (X’s and O’s) on the scale are audible, meaning you can hear them.   If the sounds occur above the threshold measurement they would be inaudible.  Ranges of hearing loss have been established and are listed as follows:

0 dB to 20 dB = Normal range

21 dB to 40 dB = Mild hearing loss

41 dB to 60 dB = Moderate hearing loss

61 dB to 80 dB = Severe hearing loss

81 dB+ = Profound hearing loss

This explanation of the audiogram was designed to familiarize you with basic understanding of the hearing test but is only one piece of the puzzle.  There are other components to the complete hearing evaluation that when combined with the audiogram provide a comprehensive view of your hearing, allowing the audiologist to make the most appropriate treatment recommendations.

It is important to be familiar with your audiogram.  It is a useful tool in helping us understand how we hear and provides a picture of your hearing profile and by having your hearing tested regularly will allow you to track the results over time.  Basic understanding of the components of the audiogram allow you to be proactive in your hearing health.   Get to know your audiogram!

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