CSD 301 Introduction to Audiology Quiz

Introduction to Audiology - CSD 301

• Course name: CSD 301 Introduction to Audiology
• Fall 2024

Announcements/Reminders

• Sign-up for part 2 of the audiogram package project. Instructions and audiogram forms are posted on Canvas.
• Optional one-time otoacoustic emissions hands-on lab (ungraded) on Friday, Nov. 8 from 2:00 – 3:00 pm (maximum 10 students). Sign-up is available.
• Homework #5 will be posted today and due on Tuesday, Nov. 12 at 3:30 PM or before.

Physiologic Tests of Auditory Function

• Objective measures of auditory function.
• These tests do not measure hearing ability.
• Common clinical measures include:
  • Otoacoustic Emissions (OAE) Test
  • Tympanometry
  • Acoustic Reflex Threshold (ART) Test
  • Acoustic Reflex Decay Test
  • Auditory Brainstem Response (ABR)

Otoacoustic Emission (OAE)

• Low-level sounds generated within the inner ear by outer hair cells (OHC) that propagate back to the outer ear canal.
• Index of outer hair cell activity; normal, healthy ears produce emissions. Damaged OHCs reduce OAE production.
• Measured by placing a probe into the ear canal.
• Objective, non-invasive measure of OHC function, commonly used for newborn hearing screenings and for any age.

Types of Otoacoustic Emissions

• Spontaneous Otoacoustic Emissions (SOAEs):
  • Occur naturally, in the absence of external sound, produced by outer hair cells as they move
  • Emissions are less than 10 dB SPL(but can be as high as 40 – 50 dB SPL)
  • Common, but not present in all normal hearing individuals.
• Sound-Evoked Otoacoustic Emissions:
  • Require an auditory stimulus (e.g., clicks, pure tones) to evoke a response
  • Used clinically

Evoked Otoacoustic Emissions

• TEOAE:
  • Stimuli: short duration wide-band clicks or chirps.
  • Stimulus level: ~84 dB SPL.
  • Probe placement: single probe.
  • Clinical use: universal, newborn hearing screening
  • Response/Interpretation: absent if ≥ 20-30 dB HL threshold; Signal-to-Noise Ratio
• DPOAE:
  • Stimuli: 2 pure tones.
  • Stimulus level: L1 = 65 dB SPL, L2 = 55 dB SPL.
  • Probe placement: dual probes.
  • Clinical use: differential, diagnosis (children, adults), ototoxicity monitoring, can be used on those with moderate hearing losses (≤ 60 dB HL).
  • Response/Interpretation: DP levels mainly (SNR also valuable)
• SFOAE:
  • Stimuli: single pure tone, low-moderate levels (45 – 60 dB SPL).
  • Probe placement: same as TE’s and DPs.
  • Clinical use: research focus
  • Response/Interpretation: SF levels (ongoing research)

Otoacoustic Emissions

• Present OAE:

  • Indicates normal outer hair cell (OHC) function, which often correlates with normal hearing sensitivity.
  • Indicates proper ear function (conductive mechanism) including proper transmission pathways, no blockage of external auditory canal, a functioning tympanic membrane movement, and impedance matching system.

• Limitations:

  • Does NOT evaluate inner hair cells (IHC), cranial nerve VIII, or the ascending central auditory pathway or auditory processing.

OAE Testing Considerations

• Clear ear canal: no obstructions or excessive wax.
• Active ear infections: do not test.
• Instructions for older children/adults: insert probe, listen for clicks/tones, sit quietly. Testing is brief.

Auditory Evoked Potentials (AEPs)

• Measurement/Interpretation of neural electrical activity in response to auditory stimuli.
• Types:
  • Electro Cochleography (EcochG)
  • Auditory Brainstem Response (ABR)
  • Middle Latency Response
  • Late Latency Response

Auditory Brainstem Responses (ABR)

• Neurological test of the 8th cranial nerve and brainstem function.
• Exogenous/stimulus-dependent response. Unaffected by arousal state (e.g., sleep).
• Commonly used for:
  • Estimation of auditory sensitivity
  • Newborn hearing screening
  • Neurodiagnosis
  • Intraoperative monitoring

Auditory Brainstem Response (ABR) Generation

• Components, Distal/Proximal portions of the 8th cranial nerve
• Waves: I, III, V (interpreted for clinical use)

Example of ABR Recording

• Testing begins at 90 dB nHL (one ear at a time), testing in decreasing intensities.
• Two recordings for each intensity (why?).
• Lowest intensity identifying wave V is the ABR threshold.

ABR Interpretation (Neurologic Test)

• Wave V component (largest trough) of the response.
• Latency: time for wave components (transmission speed); prolonged latency associated with retrocochlear lesion
• Amplitude: neuron firing (#); decreases as stimulus level decreases
• Interwave Intervals: time needed between peaks
• V-v Interaural: latency difference between ears (prolonged indicates retrocochlear pathology)

ABR Normative Data

• Normal ranges for absolute latencies (I, III, V).
• Normal ranges for interwave intervals (I–III, III–V, I–V).
• Normal range for interaural latency (V–v).

ABR Interpretation (Hearing Threshold Estimation)

• Wave V is crucial for identifying ABR threshold.
• Lowest intensity level clearly identifying wave V defines the ABR threshold.
• Correcting for a factor (-15 dB to -20 dB) yields equivalent hearing levels for audiograms.

Estimating Hearing Threshold From ABR

• Applying correction factor to identify threshold.
• Estimated equivalent hearing level (eHL) for the ear.
• eHL applies to 1000-4000 Hz.

ABR Latency & Intensity Relationship

• Latency increases with decreasing stimulus intensity.
• Wave amplitude decreases with decreasing intensity.
• Waves I and III disappear closer to the threshold.
• Wave V is the most robust to stimulus intensity changes.

ABR Patterns for Various Pathologies

• Normal: all latencies within normal limits (WNL); good morphology
• Conductive hearing loss: I wave markedly delayed, other measurements WNL, good morphology
• Sensory hearing loss: I slightly delayed, I wave may be small or absent, other measurements WNL, poor morphology
• Neural hearing loss: I wave normal or slightly delayed, I–III latency delayed, other measurements delayed, poor morphology

Factors Affecting ABR

• Environmental (electrical, acoustical).
• Subject-related factors (age, gender, state of consciousness and arousal, body temperature).
• Examiner-related factors (training, education, scope of practice).

Maturation of the ABR

• Wave V latency of a newborn is approximately 5 milliseconds.

Summary for ABR

• Assess/evaluate 8th nerve function and brain stem
• Not affected by sleep (good for newborns).
• Use for new born hearing screening, hearing threshold estimation (for those unable to perform behavioral audiometry).
• Primary auditory brainstem pathways present at birth, but mature over time.
• ABR waveform near normal adult response around 1 year of age.

Test your understanding of the fundamentals of audiology covered in CSD 301. This quiz focuses on the physiologic tests of auditory function, including otoacoustic emissions and other clinical measures. Prepare to assess your knowledge on various auditory tests and their significance in clinical settings.