03 Hearing loss and pure tone audiogram

Question 1

What is conductive hearing loss?

Answer 1

Conductive hearing loss is a type of hearing loss due to transmission problems, where a medical approach might be used.

Question 2

What does an audiogram show?

Answer 2

An audiogram shows the hearing threshold for pure tones with frequencies in the range of the human voice from 125 Hz to 8000 Hz.

Question 3

Why is the decibel scale used for sound?

Answer 3

The decibel scale is used for sound because it is a logarithmic scale. Human hearing is said to be logarithmic too

1. Human sensation is logarithmic
2. Transfer function is easy to calculate
3. Presents a large range of magnitudes

Question 4

What is sensorineural hearing loss?

Answer 4

Sensorineural hearing loss is a type of hearing loss due to perception problems, where a technical device might be used.

Question 5

What is hearing loss due to transmission issues called? And what causes it?

Answer 5

Conductive hearing loss. It can be caused by issues such as ear infections, fluid in the middle ear, perforated eardrum, or obstructions like earwax.

Question 6

What is hearing loss due to perception issues called? What causes it and which part of the ear is affected?

Answer 6

Sensorineural hearing loss. it is caused by damage to the inner ear or the auditory nerve.

Question 7

What is the relationship between perception, transmission, and hearing loss?

Answer 7

Perception of sound interaction is called hearing, but before sound can be perceived, transmission of that sound is needed.

Question 8

What are decibels (dB) often misperceived as?

Answer 8

Decibels are often misperceived as a unique dimension unit for sound, but dB alone defines solely a ratio or a factor.

Question 9

What is the decibel hearing level (dB HL)?

Answer 9

Decibel hearing level (dB HL) is a unit of measurement used to quantify the degree of hearing loss or the sensitivity of an individual’s hearing, relative to a standardized reference level.

Question 10

What is the decibel sound pressure level (dB SPL)?

Answer 10

The decibel sound pressure level (dB SPL) is a logarithmic measure of the pressure of a sound relative to a reference pressure, typically 20 micropascals, which is considered the threshold of hearing for humans.

Question 11

Why does sensorineural hearing loss affect both air conduction and bone conduction?

Answer 11

Because it originates from a problem in the inner ear or neural pathway leading to the brain.

So air & bone conduction are not interrupted but due to a deeper issue in the inner ear, the hearing level is still affected

Question 12

What is the difference between the dB SPL and the dB HL?

Answer 12

dB SPL (Sound Pressure Level) measures the absolute sound pressure relative to a reference pressure (20 µPa), while dB HL (Hearing Level) measures the minimum sound level that an average human ear can hear at different frequencies, based on a reference audiometric zero.

Question 13

Why does the force provided to the stapes from the incus need to be amplified compared the force coming from the tympanic membrane?

Answer 13

The cochlea is fluid filled so a lot of sound energy would be lost going from the air to water. Amplifying the force helps in the transfer

Question 14

What are the two main mechanisms by which the outer and middle ear transmit sound?

Answer 14

1. Surface Matching: The entire sound force across the large surface of the tympanic membrane is transformed into a much smaller surface of the stapes, increasing pressure.
2. Lever: The handle of the malleus is slightly longer than the long process of the incus, increasing the force provided to the stapedial footplate. (overall, malleus is longer and incus is shorter)

Question 15

What is the global notation for air and bone conduction audiograms?

Answer 15

R-R-R (Right, Round, red)

Question 16

What is tonotopy in the basilar membrane?

Answer 16

Tonotopy in the basilar membrane refers to the spatial arrangement of frequency responses along its length, where different frequencies of sound are processed at specific locations. Higher frequencies are detected at the base (start), while lower frequencies are processed at the apex (end).

Like a piano, each place in the basilar membrane has a specific frequency

Question 17

What is the role of hair cells in hearing sensation?

Answer 17

When the amplitude of the basilar membrane motion is high enough to deflect the bundles of the inner hair cells, an electrical signal is generated, leading to hearing sensation.

Question 18

What is the Air-Bone Gap (ABG)?

Answer 18

The Air-Bone Gap (ABG) is the difference between air conduction (AC) and bone conduction (BC) thresholds, indicating the degree of conductive hearing loss.

Question 19

What are the risks associated with cytocochleograms?

Answer 19

Even though you may have dramatically different levels of hair cell damage, the measurements taken in just a few areas may indicate a similar level/pattern

Question 20

What does the term ‘crossover’ refer to in audiometry?

Answer 20

Crossover refers to the phenomenon where sound transmitted through bone conduction allows the patient to hear the tone in the non-tested contralateral ear.

Question 21

What is the process of masking in audiology?

Answer 21

Masking in audiology involves playing narrow band noise into the non-tested contralateral ear to prevent crossover of pure tones from the test ear.

Question 22

What does a cytocochleogram represent?

Answer 22

The cytocochleogram represents the state of all hair cells in the cochlea, providing an estimation of hearing sensation at all frequencies.

Question 23

What is the significance of the hearing threshold at 0 dB HL?

Answer 23

The hearing threshold at 0 dB HL represents the averaged hearing threshold of healthy subjects, indicating the lowest sound pressure levels perceptible by an average person.

Question 24

What is pure tone audiometry?

Answer 24

Pure tone audiometry is a subjective test for clinical diagnosis of hearing, determining the hearing threshold for pure tones with frequencies between 125 Hz and 8000 Hz.

Question 25

Which parts of the basilar membrane influence the fundamental frequency?

Answer 25

The width, tension and density at each point

Question 26

What distinguishes air conduction (AC) and bone conduction (BC) measurements?

Answer 26

In air conduction (AC), sound is transmitted across the outer and middle ear to the inner ear. In bone conduction (BC), vibrations bypass the outer and middle ear structures and stimulate the inner ear directly.

Question 27

What is the purpose of outer hair cells (OHC)?

Answer 27

The purpose of outer hair cells (OHC) is to amplify sound signals and enhance the sensitivity and frequency selectivity of hearing by changing their length in response to sound vibrations.

They increase the amplitude of the basilar membrane motion around the characteristic frequency. Increased BM motion increases motion of cochlea fluid which leads to stronger inner hair cell deflection

Also amplifies low intensity/soft sounds

Question 28

What is a tuning curve in the context of hair cells?

Answer 28

A tuning curve illustrates how outer hair cells act as active amplifiers, increasing the amplitude of the basilar membrane motion around the characteristic frequency.

Question 29

What is the significance of the Decibel Hearing Level (dB HL) scale?

Answer 29

The dB HL scale is based on psychoacoustic measurement and is averaged from a large number of healthy hearing subjects.

Question 30

What does the term ‘mixed hearing loss’ indicate?

Answer 30

Mixed hearing loss indicates that both sound transmission and sound perception are deteriorated.

AC doesn’t equal BC
But BC is also not at dB HL 0

Question 31

What is the formula for calculating the combined sound pressure of two independent sources?

Answer 31

To find the combined sound pressure level, convert dB to absolute values, add them, and then convert back to dB.

Question 32

What is the relationship between AC and BC hearing thresholds when AC is left 50 dB lower than BC right?

Answer 32

AC left is 50 dB lower than BC right, and BC left is 5 dB lower than BC right.

Question 33

What is maximal masking?

Answer 33

The crossover from the noise at the tested ear needs to be smaller than the perceived pure tones.

Potential conductive hearing loss makes this more complicated because the aur-bone gap has to be considered. Also the masking has to be done for every frequency in both ears in air- and bone conduction. Therefore it’s only used in complex clinical cases

Question 34

What is minimal masking?

Answer 34

The masking noise level perceived at the masking ear needs to be greater than the crossover of the pure tones from the test ear

Question 35

What are the 2 types of masking that can be applied?

Answer 35

Minimal masking

Maximal masking

Question 36

What is needed to exclude potential errors when a patient cannot indicate a specific side of hearing?

Answer 36

Masking is needed to exclude potential errors.

This is the act of playing a narrow band noise into the non-test ear to prevent crossover

Question 37

What is the challange of masking in audiology?

Answer 37

The challenge of masking in audiology is to ensure that the sound presented to one ear does not cross over and affect the hearing assessment in the other ear, which can lead to inaccurate results.

Essentially, applying the right level of masking noise.

Question 38

When is masking needed?

Answer 38

• When the AC threshold measusred with headphones) is 50 dB worse than BC threshold in opposite ear
• If BC threshold is equal or worse than the opposite ear and if the AC-BC difference of the measuring ear is 5dB or more (MUST BE BOTH FOR THIS 2ND CONDITION)

Question 39

What is the result of the thresholds with masking?

Answer 39

There is no change of the thresholds with the masking; therefore, the thresholds are confirmed.

Question 40

What is the masking recipe? (5 steps)

Answer 40

1. Start: 20 dB over the AC threshold of the masking ear
2. Measure the threshold
3. Increase masking level by +10 dB
4. Re-measure the threshold
5. Is the threshold the same as step 2 & 4? If yes, threshold is determined. If no, back to step 3.

Question 41

What is indicated by the absence of an air-bone gap (ABG)?

Answer 41

The absence of an ABG suggests that there is no conductive hearing loss.

Question 42

What do the x-axis and y-axis represent in the audiogram graphs?

Answer 42

The x-axis represents frequency in Hz from 125 to 8000 Hz, and the y-axis represents hearing level in dB from 0 to 130 dB.

Question 43

What does the pattern of points in the audiogram suggest about hearing sensitivity?

Answer 43

The pattern of the points suggests a downward trend, indicating a decrease in hearing sensitivity as frequency increases.

Question 44

What does sensorineural hearing loss typically affect?

Answer 44

Sensorineural hearing loss typically affects the ability to hear high frequencies.

Question 45

What is the frequency range displayed in the audiogram graphs?

Answer 45

The frequency range displayed in the audiogram graphs is from 125 to 8000 Hz.

Question 46

What are 2 examples of subjective hearing tests?

Answer 46

Speech audiometry: Speech intelligibility for different sound pressures

Speech in noise tests: Speech intelligibility tested in noisy environments

Question 47

What is the significance of a graph showing hearing loss at different frequencies?

Answer 47

It indicates that there is a potential hearing loss at those frequencies, which may be assessed further.

Question 48

If a patient had conductive hearing loss on the left side and a sound is played on the left side of their head, which side would they indicate they heard the sound from?

Answer 48

Right side. Thus is called crossover sound. Bone conduction allows the patient to hear the sound in the other ear

Question 49

Until what level (dB) is the hearing level considered normal?

Answer 49

Until 20-30 dB. If the hearing level of the patient exceeds that, the ear is considered pathological.