Week 2 Anatomy, Physiology, Diagnostic Assessment, and Audiometric Interpretation of the Human Auditory System

Rinne Test (AC versus BC Comparison)

Alternates holding a vibrating tuning fork near the EAC opening (AC) and pressing the stem against the mastoid process (BC).

Air Conduction (AC) Hearing Pathway

Sound that passes through the outer ear, middle ear, inner ear, and beyond

• Sound presented via headphones or inserts

Bone Conduction (BC) Hearing Pathway

Sound that bypasses the outer and middle ear by vibrating the skull and stimulating the inner ear directly

• Sound presented via bone conduction vibrator

Weber Test (Test of Lateralization)

A vibrating tuning fork stem is held firmly against the midline of the patient's skull then asked where the sound is heard (left ear, right ear, both ears, or midline)

Weber test: Sound lateralizes to poorer ear

Indicates a Conductive Hearing Loss (CHL) in affected ear

Weber test: Sound lateralizes to better ear

Indicates a Sensorineural Hearing Loss (SNHL) in the opposite ear.

Conductive Hearing Loss (CHL)

Caused by structural abnormalities, blockages, or pathology in the outer ear (OE) and/or middle ear (ME).

Sensorineural Hearing Loss (SNHL)

Caused by damage to sensory structures within the cochlea (sensory) and/or Cranial Nerve VIII / auditory pathways (neural).

Mixed Hearing Loss

A combination of conductive (OE/ME) and sensorineural (cochlear/neural) pathology in the same ear.

Normal Hearing

0 to 25 dB

Slight hearing loss

15 to 25 dB (Peds standard)

Mild hearing loss

25 to 40 dB

Moderate hearing loss

40 to 55 dB

Moderately-severe hearing loss

55 to 70 dB

Severe hearing loss

70 to 90 dB

Profound hearing loss

90 to 120 dB

How to interpret hearing loss

Amount, Type, Which ear

Right Ear

AD and Red

Left Ear

AS and Blue

Air-Bone Gap (ABG)

The mathematical difference between the Air Conduction threshold and the Bone Conduction threshold at a specific frequency

ABG calculation

ABG = AC threshold - BC threshold

ABG is within normal limits when:

Equal to or less than 10 dB

ABG is clinically significant abnormal when:

Equal to or greater than 15 dB

Normal hearing thresholds

• AC thresholds: $\le 25\text{ dB HL}$.

• BC thresholds: $\le 25\text{ dB HL}$.

• Air-Bone Gap: $\le 10\text{ dB}$.

Sensorineural hearing loss thresholds

• AC thresholds: $> 25\text{ dB HL}$.

• BC thresholds: $> 25\text{ dB HL}$.

• Air-Bone Gap: $\le 10\text{ dB}$ (no abnormal ABG).

Conductive hearing loss thresholds

• AC thresholds: $> 25\text{ dB HL}$.

• BC thresholds: $\le 25\text{ dB HL}$ (normal bone conduction sensitivity).

• Air-Bone Gap: $\ge 15\text{ dB}$ (abnormal ABG present).

Mixed hearing loss thresholds

• AC thresholds: $> 25\text{ dB HL}$.

• BC thresholds: $> 25\text{ dB HL}$ (impaired bone conduction sensitivity).

• Air-Bone Gap: $\ge 15\text{ dB}$ (abnormal ABG present).