Use a 512 Hz tuning fork.There are 2 pathways by which sound waves reach the cochlea, which then sends impulses down the 8th cranial nerve to the brain’s auditory cortex:
- Air conduction: How we hear the world. Airwaves travel through the external auditory meatus, down the canal to the TM. Vibrations are picked up by the middle ear ossicles, transmitted to the cochlea.
- Bone conduction: How we hear ourselves talk. Internal vibrations resonate through the cranium, are picked up directly by the cochlea.
- Conditions interfering with normal air conduction cause a “conductive hearing loss.”
- These include was in canal, large TM perforations, middle ear effusions (infections or sterile), middle ear masses (rare), Eustachian Tube dysfunction
1. Show pt. tuning fork & explain, “I’m going to put this on your head & you’ll hear a buzz.”
2. Strike fork hard, Place vibrating fork on the skull
3. Ask, “Do you hear it better on the Right, better on the Left, or equally in Both ears?”
4. Chart: “Weber lateralizes to ___” (or “Weber: no lateralization”)** Vibration is heard better in (“lateralizes to”) ear with conductive loss
- Since ambient airwaves can’t get through the conductive obstruction, the nervous system sensitizes that cochlea to amplify sound on that side
- So bone conduction (tuning fork on skull) is heard very well; on the other side, which is still able to pick up ambient sounds, the noise is perceived as less loud
- Try it: Stick a finger in one ear and Hum. You’ll hear it best in the ear with finger (conductive deficit)
- If there’s no conductive deficit, vibrations arrive equally at both cochlea.
- From there to the cerebral cortex, any sensorineural deficit results in less sound.
Rinne Test: [pronounced Rin-NAY]
** Compare vibrating fork on bone vs. through air** How to Perform (my way [quicker than others])
- Instruct pt., “Tell me which is louder, ‘ONE’ or ‘TWO’.”
- Strike fork hard, place handle on pt’s mastoid (prongs facing back), say “This is ‘ONE’.” [BC]
- Then place prongs by external auditory meatus (entrance to canal), say “This is TWO’.” [AC]
- If #2 is louder, air conduction is greater than bone (AC > BC)
- If #1 is louder, bone is greater than air (BC > AC)
- If BC > AC (or if BC = AC), there’s a conductive deficit in that ear
- If AC > BC, there’s no conductive deficit
- If there’s a hearing deficit in an ear, but no conductive deficit, then the hearing disorder is sensorineural
Clinical Scenarios1. Conductive Deficit on Right [Left Ear normal]
- Decreased hearing on Right (by whisper test or audiometry)
- Weber lateralizes to Right
- Rinne — Right Ear: BC > AC; Left Ear: AC > BC
- Decreased hearing on Right
- Weber lateralizes to Left
- Rinne — AC > BC bilaterally
Something to NoticePeople with conductive hearing loss speak quietly (because they hear themselves so well).
- Have you noticed how we whisper during airplane descents (conductive loss due to Eustachian Tube dysfunction)
- If you must tell Grandpa not to shout, be gentle about it