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Tympanometry

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Objectives

• Identify the uses and limitations of tympanometry and SGAR in the diagnosis of otitis media

• Interpret representative tympanograms with proficiency

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How Tympanometry Works

1. Emits fixed frequency tone

2. Measures reflected sound – converts measurement to compliance (volume)

3. Varies pressure from +400 to -600 daPa

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Tympanometry

Janet Stockard Sullivan 2003

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What does Tympanometry tell us?

• If sound energy is being lost in the outer or middle ear due to fluid, vernix, anatomical abnormalities, etc. (conductive component to loss) help confirm otoscopy

• Provides cross-check with bone conduction• Had poor sensitivity in the past due to adult

settings being used in infant ears (different!).• Now more appropriate equipment settings

(1000 Hz probe tone) and normative data for infants is available.

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Interpretation of Tympanogram

Three core features of tympanogram:1) Compliance

2) Middle ear pressure

3) Shape of the curve

4) Ear canal volume

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Interpretation of Tympanogram

• Compliance – High (> 0.5 mL)– Intermediate (>0.2 to < 0.5 mL)– Low (< 0.2 mL)

• Pressure– Normal -100 to +50 daPa– High Negative <-100 daPa– High Positive > +50 daPa

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Interpretation of Tympanogram

• Shape of Curve– The peak may appear sharp, rounded, or flat. The

peak will appear sharp in the absence of middle ear effusion and flat when middle ear effusion is present

• Ear Canal Volume– Normal volume 0.5- 1 mL– Reduced volumes may occur when the ear canal

is impacted by cerumen– Elevated volumes may occur when the tympanic

membrane is perforated

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Tympanometry• Amount of energy transmitted directly

proportional to compliance

• While emitting sound (energy) pressure is varied

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Tympanometry

• Eardrums moves most easily when pressure equal on both sides of ear = when ear is most compliant

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Your Turn!

• Which curve has the lowest compliance?

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Tympanometry

• Compliance can be classified as High (> 0.5 mL), Intermediate (>0.2 to < 0.5 mL), or Low (< 0.2 mL)

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Which of the curves was obtained from a

retracted eardrum? Middle ear pressure can be classified as: Normal -100 to +50 daPa, High Negative <-100 daPa , High Positive >

+50 daPa.

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Which of the following is true?

• Effusion likely

• Effusion unlikely

• Equivocal

Even though there is a high negative pressure (-230 daPa), effusion is unlikely because of the high compliance(0.6 mL) and sharp peak

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Which of the following is true?

A. Effusion Likely

B. Effusion Unlikely

C. Equivocal

Given an intermediate compliance (0.4), high middle ear pressure (+100) and a rounded curve, the diagnosis is equivocal.

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Which of the following is true?

A. Effusion Likely

B. Effusion Unlikely

C. Equivocal

Given an intermediate compliance (0.3 mL), high negative pressure (-195 daPa), and a round peak, the diagnosis is equivocal.

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1. Normal Ear Canal Volume2. No Mobility3. No Middle-ear Pressure4. No GR

POSSIBLE CAUSE1. Fluid-filled Middle-ear 2. Compliance Peak May be Present at a Much More Negative Pressure Than -400daPa

A normal ear canal volume is 0.5- 1 mL

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Why is this not cerumen impaction or perforated eardrum?

Normal Ear Canal Volume

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1. Abnormal Ear Canal Volume (large)2. No Mobility3. No Middle-ear Pressure4. No GR

POSSIBLE CAUSE1. Open Perforation2. Patent Pressure Equalization (P-E) Tube

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Spectral Gradient Acoustic Reflectometry (SGAR)

• How it works:– The device emits a sound into the ear canal– Rather than measure the energy of reflected

sound as is done in tympanometry, SGAR analyzes the frequency spectra of the reflected sound

– The angle of the curve of the frequency spectrum is measured

– ADVANTAGE: no seal needed!

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Spectral Gradient Acoustic Reflectometry (SGAR)

<49o High

49-59o Moderate to High

60-69o Moderate

70-95o Low to moderate

>95o Low

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Interpreting SGAR

• In an ear without effusion, most of the sound is absorbed and that which is reflected back has a wide spectral gradient angle. In a middle ear containing an effusion, most of the sound is reflected back and has a narrow spectral gradient angle. The angles correlate with probability of effusion

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SGAR

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Interpreting SGAR

• SGAR should be used with caution due to questionable accuracy. As stated in the American Academy of Pediatrics 2004 Otitis Media with Effusion Clinical Practice Guidelines “validation studies primarily have used children 2 years old or older with a high prevalence of OME.”

• A recent study at University of Pittsburg focusing on the use of SGAR in children ages 6 –24 months, found a sensitivity of 46% and a specificity of 91%.

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