Audiology Study Guide

📖 Core Concepts Audiology – scientific study of hearing, balance, and related disorders. Behavioral hearing test – patient‑response test to determine sound‑level thresholds. Otoacoustic emissions (OAEs) – sounds generated by outer hair cells; indicate cochlear (inner‑ear) health. Auditory Brainstem Response (ABR) – electrophysiologic test that records neural activity from auditory nerve to brainstem. Tympanometry – measures middle‑ear pressure/compliance to detect fluid, perforations, or ossicular problems. Frequency ranges – low (≈250–500 Hz), middle (≈1000–2000 Hz), high (≈4000–8000 Hz). Severity of loss – mild (16–25 dB), moderate (26–40 dB), moderately‑severe (41–55 dB), severe (56–70 dB), profound (>70 dB). Site of lesion – outer ear, middle ear, inner ear (cochlea), auditory nerve, central auditory pathway. Speech banana – region on an audiogram where most speech phonemes appear; used to gauge functional hearing. --- 📌 Must Remember Screening → Diagnosis → Intervention is the care pathway. OAEs present → cochlear (outer‑hair‑cell) function intact; absent OAEs suggest cochlear loss. ABR waves I–V: I = auditory nerve, V = midbrain; delayed/absent waves indicate neural pathology. Tympanometry types: Type A – normal middle‑ear pressure/compliance. Type B – flat curve → fluid or perforation. Type C – negative pressure → eustachian tube dysfunction. Candidacy for cochlear implant: severe‑to‑profound sensorineural loss, limited benefit from hearing aids, intact auditory nerve. Bone‑anchored hearing aid (BAHA) is indicated for conductive or mixed loss when conventional aids not feasible. Noise‑induced hearing loss shows a “dip” at 4000 Hz (the “noise notch”). --- 🔄 Key Processes Behavioral Audiometry (Pure‑tone air‑ and bone‑conduction) Present tones → patient signals hearing → plot threshold per frequency → derive audiogram. OAE Screening Deliver click/tones → microphone in ear canal records emissions → presence = normal cochlear outer hair cells. ABR Testing Place electrodes (vertex, mastoid, forehead) → deliver click stimuli → record wave latency/amplitude → assess neural integrity. Tympanometry Insert probe → vary ear‑canal pressure → record compliance curve → classify type (A, B, C). Hearing‑Aid Fitting Perform real‑ear measurement → select appropriate gain based on DSL/NAL formula → verify with speech‑map. Cochlear Implant Mapping Set threshold (T‑levels) and comfortable (C‑levels) for each electrode → fine‑tune using patient feedback & objective measures. --- 🔍 Key Comparisons OAEs vs ABR – OAEs test cochlear outer‑hair‑cell function (pass/fail); ABR tests neural pathway integrity (latency/amplitude). Air‑conduction vs Bone‑conduction thresholds – Air includes outer/middle ear; bone bypasses them. Conductive loss = air > bone; sensorineural loss = air ≈ bone. Hearing aid vs BAHA – Conventional aid amplifies sound acoustically; BAHA transmits vibrations through bone, bypassing outer/middle ear. Type A vs Type B Tympanogram – Type A = normal middle ear; Type B = flat, suggests fluid or perforation. --- ⚠️ Common Misunderstandings “Absent OAEs = permanent hearing loss.” – OAEs can be absent transiently (e.g., middle‑ear fluid) even with normal hearing. “All tinnitus needs medication.” – Most tinnitus management relies on counseling and sound therapy, not drugs. “A normal ABR rules out any hearing loss.” – ABR detects neural deficits; mild cochlear loss may still show a normal ABR. “High‑frequency loss only affects music.” – High frequencies carry consonants; loss severely impairs speech intelligibility. --- 🧠 Mental Models / Intuition “Gatekeeper” model: Think of the ear as three gates (outer, middle, inner). Problems at each gate produce characteristic test patterns (e.g., conductive loss = air‑bone gap). “Signal‑to‑Noise” analogy: OAEs are the ear’s “self‑noise”—if you can hear the ear’s own sound, the cochlea is healthy. “Wave‑train” for ABR: Each ABR wave is a train car; if a car (wave) is missing or delayed, the track (neural pathway) is damaged at that segment. --- 🚩 Exceptions & Edge Cases Middle‑ear effusion can cause absent OAEs despite normal cochlear function. Auditory neuropathy – present OAEs but abnormal ABR; indicates neural dysfunction despite healthy outer hair cells. Cochlear implant candidacy may be granted even with residual low‑frequency hearing (Hybrid CI). Hyperacusis can coexist with normal audiogram; diagnosis relies on loudness discomfort levels, not thresholds. --- 📍 When to Use Which Screening newborns: Use OAEs (fast, objective) → follow‑up with ABR if fail. Distinguish conductive vs sensorineural: Perform both air‑ and bone‑conduction pure‑tone audiometry. Suspected retrocochlear pathology: Order ABR (waves I–V) and possibly MRI. Middle‑ear pathology suspicion: Use tympanometry first; if type B/C, consider otoscopy/medical referral. Rehabilitating severe‑to‑profound loss: Evaluate for cochlear implant candidacy before hearing‑aid trial. --- 👀 Patterns to Recognize Air‑bone gap > 10 dB on audiogram → conductive component. Flat tympanogram (Type B) + absent OAEs → middle‑ear fluid. ABR wave V latency > 5.5 ms → possible auditory neuropathy or brainstem delay. Noise notch at 4 kHz → classic noise‑induced hearing loss. Speech banana truncated at high frequencies → high‑frequency sensorineural loss affecting speech consonants. --- 🗂️ Exam Traps Distractor: “OAEs absent → always sensorineural loss.” – Wrong; middle‑ear issues can also suppress OAEs. Distractor: “Type C tympanogram indicates perforated eardrum.” – Wrong; Type C reflects negative middle‑ear pressure, not perforation. Distractor: “All patients with tinnitus need a cochlear implant.” – Wrong; most are managed with counseling and sound therapy. Distractor: “Bone‑anchored hearing aids are only for children.” – Wrong; indicated for adults with conductive loss when conventional aids fail. Distractor: “If ABR is normal, hearing aids are unnecessary.” – Wrong; ABR assesses neural integrity, not threshold level; a patient may still need amplification.