Ear canal volume Flashcards
What diagnostic measures does ear canal volume affect?
- Pure tone thresholds
- Acoustic immittance (tympanometry & ARTs)
- OAEs
What affects tympanometric assessment?
- Insertion depth of the probe
- Individual’s ear canal dimensions
- Any cerumen in the external auditory meatus
How does tympanometry indicate possible outer/middle ear pathology?
- Large volume indicates tympanic membrane perforation
- Small volume indicates cerumen impaction
Describe how ear canal volume changes with age.
- Infants have smaller ear can volumes than adults
- Ear canal volume is equivalent to an adult’s by 2 years of age
How can tympanometry be evaluated in the pediatric populations?
- Tympanometry uses a 226-Hz tonal activator
- This tonal activator is not an effective test for middle ear function in newborns
- A 1000-Hz tonal activator can be used in infants <4 months old
- By 6 months of age, the 226-Hz tonal activator can be used
How can acoustic reflex thresholds be evaluated in the pediatric populations?
- The stapedial muscle reflex is present at birth and can be measured in infants using a 1000-Hz tone
Why should caution be used when assessing ARTs in infants?
- Every time a cavity is reduced by half its size, the sound pressure level increases by 6 dB SPL
- Stimuli for ART assessment are presented at high intensities and can cause damage to young infant ears
What can occur when assessing pure tone thresholds under supraaural earphones?
- Standing waves
- Collapsed ear canals
Why do standing waves occur?
- Standing waves commonly occur around 8000 Hz
- Standing waves occur when the stimulus presented from the transducer is reflected off of the tympanic membrane and cancels out the incoming stimulus
- Standing waves can be avoided by using insert earphones
Why do collapsed ear canals occur?
- Collapsed ear canals narrow or completely collapse the ear canal
- Collapsed ear canals result in false hearing thresholds in the high frequencies
- Collapsed ear canals can be avoided by using insert earphones
What is the prevalence of collapsed ear canals in the pediatric and adult ear canals?
3.5% during preschool hearing screenings
30% occurs in adult populations
Why are insert earphones more susceptible to calibration problems?
- They are more susceptible to calibration issues if calibrated in a 2-cc coupler
- If an individual with a PE tube is assessed with insert earphones, 15-25 dB poorer thresholds are obtained in the low frequencies when compared to supraaural earphones
- Insert earphones are not calibrated for large ear canal volumes
When should an audiologist use supraaural earphones?
When assessing pure tone thresholds in individuals with PE tubes or large tympanic membrane perforations
What impacts OAEs?
- Differences in ear canal volume
- Depth of insertion of probe fit
How does ear canal volume affect OAEs?
- Affects the stimulus delivery during recording
- Different ear canal acoustics can change the delivered stimulus from patient to patient
- Stimulus delivery can also vary between recordings if the probe tip has been removed and reinserted
- Differences in ear canal anatomy, probe fit, and depth of insertion leads to differences in impedance characteristics
- Like pure tone thresholds, OAE measurement can be affected by standing waves
How are OAEs calibrated?
2-cc coupler
- Standardized
- Does not take into consideration an individual’s ear canal acoustics
Patient’s ear
- Takes into account individual differences
- Calibration can be affected by standing waves
How do OAEs compare in children vs. adults?
OAEs will be much larger in children due to ear-canal area growth
What is insertion gain?
- The ear canal has its own natural resonance due to its volume and acoustic qualities
- When an earmold is coupled to an ear, it disrupts the ear’s natural resonance
- Hearing aid programming needs to provide amplification that results in the same sound pressure level at the tympanic membrane as if the patient was not wearing their device
What is RECD?
The difference between the output of a hearing aid recorded in a patient’s ear compared to the output recorded in the coupler.
- It is a viable verification method for young children with limited audiological data
How is RECD related to age?
- RECD values are larger in infants and decrease over a 1-month period (Bingham et al., 2009)
- By two years of age, average RECD values for pediatric patients are similar to adults (Lewis & Stelmachosicz, 1993)
When should the RECD be measured?
- At least once during the first year of the hearing aid fitting, since it cannot be predicted by a patient’s age, static immittance, or equivalent ear canal volume
- Individual measurements ensure that prescriptive targets are being met, which will result in increased speech audibility (McCreery et al., 2013)
How can the RECD be measured?
- Can be measured with a patient’s earmold or with a foam probe tip
- Measurement with the patient’s earmold allows the acoustics of the earmold, as well as the acoustics of the patient’s ear canl to be accounted
- ANSI (2013) standards stated that the standardized way to measure RECD is with the foam tip
- Given that ear canal volume varies by individual, RECDs should be measured with a child’s earmold
- Coupling the child’s earmold to the coupler can help reduce inaccuracies (Moodie et al., 2016)
