audiology ch 10

Impedance (Z)

The opposition or resistance to the flow of sound energy.

Admittance (Y)

The ease with which sound energy flows through a system.

Immittance

The combination of impedance and admittance; describes how sound energy is transmitted through the outer and middle ear.

Relationship between impedance and admittance

They are reciprocals. High impedance = low admittance. Low impedance = high admittance.

Impedance formula

Z = 1/Y

Admittance formula

Y = 1/Z

Unit of impedance

Ohms.

Unit of admittance

Millimhos (mmhos).

What does immittance audiometry evaluate?

How well sound energy is transferred through the outer and middle ear systems.

What is the cross-check principle?

Comparing results from multiple audiological tests to create a more complete picture of a patient's hearing problem or pathology.

Behavioral hearing tests

Subjective tests that require the patient's participation to evaluate their ability to hear sounds.

Objective hearing tests

Tests that usually do not require active participation from the patient.

What are the three major immittance tests?

Tympanometry, wideband acoustic immittance (WAI), and acoustic reflex testing.

Where is the probe tip placed?

At the entrance of the ear canal, where it creates an airtight seal.

What does 1 mmho approximately equal?

1 cubic centimeter (1 cm³) at volume of air at sea level.

What does tympanometry tell us?

How well the tympanic membrane and middle ear system move in response to changes in air pressure.

Is tympanometry an objective or subjective test?

Objective. The patient does not need to actively respond.

What should the patient avoid doing during tympanometry?

Swallowing, because it can change air pressure and affect the test results.

What does 0 daPa represent?

Atmospheric air pressure.

What does positive daPa represent?

Air pressure above atmospheric pressure.

What does negative daPa represent?

Air pressure below atmospheric pressure.

What is the typical pressure range used for tympanometry?

+200 to -400 daPa.

What must happen before tympanometry can be performed accurately?

The probe tip must create an airtight seal at the entrance of the ear canal.

Why is an airtight seal important?

It allows the instrument to apply and control air pressure in the ear canal.

What happens to the tympanic membrane when positive or negative pressure is applied?

The pressure reduces the ability of the tympanic membrane to vibrate, decreasing admittance.

When does the tympanic membrane move most effectively?

When the air pressure in the ear canal and middle ear are balanced, near atmospheric pressure (0 daPa).

When does maximum admittance occur in a normal ear?

Around 0 daPa, when the pressure on both sides of the tympanic membrane is balanced.

What is a tympanogram?

A graph showing how admittance changes as applied air pressure changes.

What does the peak of a tympanogram represent?

The point of maximum admittance, when the tympanic membrane moves most effectively.

What is tympanometric peak pressure (TPP)?

The air pressure at which the peak admittance occurs on a tympanogram.

What should a normal TPP be close to?

0 daPa.

What is ear canal volume?

The estimated volume of the ear canal, measured using the admittance obtained at +200 daPa.

What does a larger-than-normal Vea suggest?

A tympanic membrane perforation or pressure equalization (PE) tube.

What does a smaller-than-normal Vea suggest?

Impacted cerumen (earwax) or a clogged probe assembly.

Static acoustic admittance

how easily the middle ear allows sound energy to flow when the eardrum is at its peak movement.

What is tympanometric width (TW)?

the absolute difference between the two pressure points where the tympanogram reaches half of its maximum height.

What does an abnormally wide tympanometric width suggest?

Middle ear fluid that is accumulating or resolving.

Why should otoscopy be performed before tympanometry?

To examine the ear canal and tympanic membrane before testing and identify earwax, obstructions, or other problems.

What can happen if there is too much earwax?

It can produce inaccurate results or prevent the probe from obtaining an adequate seal.

When should tympanometry NOT be performed?

When there is active middle ear disease with ear canal drainage because fluid can enter and damage or contaminate the probe.

Type A Tympanogram (Normal Admittance)

*incert pic

What does a Type A tympanogram indicate?

Normal middle ear function, especially when there are no air-bone gaps on the audiogram.

What does Type As mean?

Shallow or stiff.

What does a Type As tympanogram suggest?

Reduced movement of the tympanic membrane.

What conditions can be associated with Type As?

Otosclerosis and some cases of otitis media.

Is Type As movement normal?

No. The tympanic membrane moves, but not enough.

Otosclerosis

abnormal bone growth that causes the stapes to become fixed or stiff.

Otitis media

fluid in middle ear

Type Ad Tympanogram (High Admittance)

*insert photo

What does Type Ad mean?

Deep or double deep.

What does a Type Ad tympanogram suggest?

Excessive movement or a highly mobile tympanic membrane.

What conditions can be associated with Type Ad?

Ossicular chain disarticulation or a thinned tympanic membrane from previous middle ear infections.

Ossicular chain disarticulation

bones are disconnected.

Type B Tympanogram (Flat)

*insert photo

What does Type B mean?

Flat; there is no noticeable change in admittance across the pressure range.

What does a Type B tympanogram suggest?

A problem affecting middle ear movement, commonly middle ear fluid (otitis media with effusion).

otitis media with effusion

infected

Type C Tympanogram (Negative Pressure)

*insert photo

What does Type C indicate?

Negative pressure in the middle ear space; the pressure is not equalized with atmospheric pressure.

What condition is commonly associated with Type C?

Eustachian tube dysfunction (ETD).

What is Eustachian tube dysfunction?

The Eustachian tube is not opening and closing properly to equalize middle ear pressure.

How can a Type C tympanogram sometimes be corrected?

Chewing or swallowing can open the Eustachian tube and help equalize pressure.

What happens if negative middle ear pressure persists?

Poor Eustachian tube function may lead to fluid accumulating in the middle ear.

What can happen when middle ear fluid develops?

the tympanogram can change from Type C to Type B.

Which probe tone is recommended for infants younger than 9 months?

1000 Hz b/c they still have birth fluid in their ears.

Which probe tone is recommended for infants younger than 9 months?

1000 Hz.

Acoustic Reflex

An involuntary, natural response to loud sounds that causes contraction of the stapedius muscles in both ears.

Is the acoustic reflex unilateral or bilateral?

Bilateral. Stimulation of one ear causes a response in both ears.

What is the purpose of acoustic reflex testing?

To evaluate the acoustic reflex pathway and help identify possible abnormalities involving the cochlea, seventh cranial nerve, eighth cranial nerve, and other parts of the pathway.

Acoustic Reflex Threshold (ART)

The lowest intensity level of a reflex-eliciting sound that produces a measurable acoustic reflex.

What is the goal when measuring ART?

Find the lowest intensity that produces a measurable reflex.

What frequencies are commonly used for acoustic reflex testing?

500 Hz, 1000 Hz, and 2000 Hz.

What is the normal ART range for tones?

75–95 dB HL.

What is the usual minimum intensity needed to produce a measurable reflex?

At least approximately 70 dB HL for most reflex-eliciting tones.

What is an ipsilateral acoustic reflex?

The reflex-eliciting tone is presented to the same ear where admittance is being measured.

What is a contralateral acoustic reflex?

The reflex-eliciting tone is presented to the opposite ear from where admittance is being measured.

What does ipsilateral mean?

Same side or same ear.

What does contralateral mean?

Opposite side or opposite ear.

If the probe is in the right ear and the stimulus is in the right ear, what is the reflex?

Right ipsilateral.

If the probe is in the right ear and the stimulus is in the left ear, what is the reflex?

Right probe / left stimulus, which is a contralateral reflex.