Middle Ear Measurements in Infants and Children — Condensed Notes

Quick clinical value and context

Acoustic immittance is quick, easy to administer, cross-checks other physiologic/behavioral measures, and does not require a behavioral response.
Useful as a low-cost, pediatric audiology tool to assess middle-ear function and hearing status.

Use a calibrated admittance instrument capable of multiple probe frequencies; daily calibration with calibration cavities.
Otoscopic examination before testing to rule out abnormalities and verify probe tip size; ensure a hermetic seal with an appropriate tip.

Testing requires the child to stay quiet and still; use enticements (toys) and an experienced assistant; parent support can help.
Seat babies/toddlers on the parent's lap during testing; animated toys and puppets are effective distractions.
Toddlers 3 years and older may not require special distraction; predictability is limited for ages 1–3 due to pain concerns.

Never ask for permission to conduct physiologic tests or discuss pain; avoid lengthy explanations.
Phrasing should be brief, e.g., "Hold still for me" or simply proceed with the test.

Acoustic impedance Z: opposition to acoustic energy flow (in acoustic ohms).
Acoustic admittance Y: ease of energy flow (in acoustic mmhos).
Two key concepts: admittance and impedance.
If the system resists motion until driving force is high, impedance is high and admittance is low.
Energy transfer: some energy reaches the cochlea; some is reflected; reflection increases with stiffness; more transmission with greater compliance.
Middle-ear impedance is shaped by three factors: stiffness, mass, and friction.
- Mass: weight of ossicles and tympanic membrane.
- Stiffness: fluid pressure load on the stapes.
- Friction (resistance): ligaments and joints.

Low-frequency probe tone (226 Hz) measures admittance vs ear-canal pressure.
Sensitive to stiffness-dominated middle ear; susceptance is dominated by the stiffness element.
In infants, 226 Hz can yield flat or notched tympanograms and may miss ME pathology.
Not reliable in very young infants due to immature outer/middle ear acoustics.

1000 Hz tympanometry is more sensitive to middle-ear status in neonates/young infants than 226 Hz.
Infant ME is mass-dominated early, shifting with age toward stiffness-dominated transmission.
JCIH 2019 guideline favors 1000 Hz probe for infants up to 9 months; 6–9 months may use either 226 Hz or 1000 Hz.
1000 Hz tympanograms in newborns tend to be single-peaked or flat, aiding differentiation of ME status.

WB tympanometry/immittance measures across a wide frequency range, not just a single low frequency.
Provides broader information on ME function and can improve identification of high-admittance pathologies.
WB absorbance/reflectance patterns help distinguish normal ME from various dysfunctions.
Device examples: first-generation wideband MEPA3; second-generation Interacoustics Titan WB; Grason-Stadler TympStar with Wideband Tympanometry.

Adults (≥18):
- Tympanometric Peak Pressure (TPP): +50 ext{ to } 200\,\text{daPa}
- Equivalent Ear Canal Volume (Veq): 0.9\text{ to }2.0\,\text{ml}
- Static Acoustic Admittance (Ytm): 0.3\text{ to }1.70\,\text{mmho}
- Tympanometric Width (TW): 51\text{ to }114\,\text{daPa}
Children (3–10 years):
- TPP: +50 \text{ to } -150\,\text{daPa}
- Veq: 0.3\text{ to }0.9\,\text{ml}
- Ytm: 0.25\text{ to }1.05\,\text{mmho}
- TW: 80\text{ to }159\,\text{daPa}
Infants and very young children require different norms; 1000 Hz and WB methods provide better sensitivity than 226 Hz.
For infants up to ~9 months, use 1000 Hz or WB measures; 226 Hz alone is often insufficient.

OME is relatively common in healthy neonates and NICU infants.
UNHS false positives are high due to transient ME conditions; accurate ME function testing helps distinguish CHL from SNHL.
Early fluid/debris in ME after birth can cause conductive hearing loss that resolves in days to weeks.
Studies show prevalence ranges around a few percent in healthy newborns; higher in NICU settings.

Use ME function testing to differentiate sensorineural hearing loss from middle-ear pathology when a newborn fails UNHS.
Reliable ME assessment reduces unnecessary alarm and guides follow-up and management.

The outer and middle ear mature after birth; the cochlea is mature at birth.
Ear canal and ME undergo substantial development during the first 6–8 months, affecting tympanometry results.
Neonatal ME is mass-dominated with higher ME resonance; by 6–9 months, ME becomes more stiffness-dominated.
Anatomical changes include EAC diameter/orientation, TM position, ossicular chain changes, and ME space expansion.

Early ME: smaller cavity, higher mass, greater compliance; results in higher resonance frequencies and different tympanogram shapes.
226 Hz measurements may misrepresent ME status in infants; 660 Hz/1000 Hz measures provide better diagnostic precision.
At birth, ME resonance frequency is around a few hundred Hz and increases with age.

Mass-dominated patterns often reflect OME with increased mobility at certain frequencies; stiffness-dominated patterns may show reduced admittance and different resonance.
Tympanometric peak height, width, and the presence/absence of a peak help differentiate ME pathology.
Notching, broad peaks, or flat curves at low frequencies may indicate ME dysfunction in infants.

Developmental changes in the external/middle ear in the first 6–8 months reduce the reliability of 226-Hz tympanometry in neonates.
1,000-Hz tympanometry and wideband measures provide greater sensitivity and specificity for ME disorders in neonates and young infants.
For infants, use 1000 Hz or wideband immittance; reserve 226 Hz for older infants/children when appropriate.
Wideband reflectance/absorbance offers advantages over traditional tympanometry by covering a broad frequency range and being less dependent on ear canal volume and probe position.