High frequency immittance testing for evaluation of the middle ear in infants

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High frequency immittance testing for evaluation
of the middle ear in infants

• Suzanne C Purdy
• National Acoustic Laboratories
• David Hartley
• Australian Hearing

ASA NSW and CCIC Seminar, Recent Developments
and Future Directions in the Hearing Assessment
and Habilitation of Young Children, Sydney, 9
Dec 2000
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Topics

• Instrumentation terminology
• Maturation of the external and middle ear
• The problem with conventional low frequency probe
  tone tympanometry
• High frequency probe tone tympanometry
• results in adults and infants with normal middle
  ears
• effects of pathology in infants
• Acoustic reflexes in infants
• Infant test protocol

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Mechanical system containing mass, spring and
frictional components
a. applied force b. velocity of a spring c.
velocity of a mass d. velocity of a frictional
component
Silman Silverman (1991)
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Immittance Terminology

• Acoustic Admittance, Ya
• the ease with which acoustic energy passes
  through a system
• the inverse of impedance
• Ya2 Ba2 Ga2
• Acoustic Susceptance, Ba
• includes mass and stiffness susceptance
• related to reactance
• Acoustic Conductance, Ga
• related to resistance

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Spring (stiffness) elements in the middle ear

• ligaments
• tendons
• the tympanic membrane
• the air enclosed in the ear canal and middle ear
  space

Van Camp et al (1986)
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Mass elements in the middle ear

• pars flacida of the tympanic membrane
• ossicles
• perilymph in the cochlea
• mesenchyme clinging to the ossicles, in infants

Meyer et al (1997) Van Camp et al (1986)
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Acoustic friction in the middle ear

• tympanic membrane
• tendons and ligaments
• the narrow passages between the middle ear cavity
  and the mastoid
• the viscosity of the perilymph and the mucous
  lining of the middle ear cavity

Van Camp et al (1986)
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Marquet et al (1973) mechanoacoustical model of
the ear containing mass, spring and friction
elements
Silman Silverman (1991)
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Immittance instrumentation
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Vector representation of admittance components
Yadmittance Bsstiffness susceptance Bmmass
susceptance Gconductance
Silman Silverman (1991)
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Grason Stadler GSI-33 Version 2

• 226, 678, 1000 Hz probe tones
• admittance (Y), susceptance (B), conductance (G)
• other instruments may measure Y phase angle

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Effect of input frequency on mass and stiffness

• Stiffness susceptance is proportional to
  frequency
• Bs increases with frequency
• Mass susceptance is inversely proportional to
  frequency
• BM decreases with frequency
• Resonance occurs when mass and stiffness
  susceptance are equal magnitude

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Resonant frequency probe tone susceptance
tympanogram
Valvik et al (1994)
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Changes in adult B, G and Y tympanograms as probe
frequency increases for different directions of
pressure change
Margolis et al (1985)
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Physical changes in infant external and middle
ear anatomy after birth (1)

• an increase in size of the external ear, middle
  ear cavity and mastoid
• a change in the orientation of the tympanic
  membrane
• fusion of the tympanic ring
• a decrease in the overall mass of the middle ear
  (due to changes in bone density, loss of
  mesenchyme)

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Physical changes in infant external and middle
ear anatomy after birth (2)

• tightening of the ossicular joints
• closer coupling of the stapes to the annular
  ligament
• the formation of the bony ear canal wall

Eby Nadol (1986) Holte et al (1991) Jaffe et
al (1970) Keefe et al (1993) Keith (1975)
McLellan Webb (1957) Saunders et al (1983).
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The external and middle ear systems vary
significantly in their acoustic response
properties over the first 2 years after birth
Keefe et al (1993) Keefe and Levi (1996)
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Normal tymp patterns in infants
Multipeaked patterns common with low frequency
probe tone in infants
Sprague et al (1995)
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Vanhuyse et al (1975) model
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Problems with 220/226 Hz probe tone in infants

• Complex patterns/notching common, making it
  difficult to use Type A, B, C classification
  scheme (Hirsch et al, 1992 Holte et al, 1991
  Keith, 1975 McKinley et al, 1997 Meyer et al,
  1997 Williams, 1992)
• Can get Type A tymps (false negatives) in ears
  with OME (Hunter Margolis, 1992 Paradise et
  al, 1976 Pestalozza Cusmano, 1980 Poulsen
  Tos, 1978 Schwartz Schwartz, 1980 Shurin et
  al, 1976 Williams et al, 1995)

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2 month old infant with left OME
Hunter Margolis (1992)
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Is a higher probe tone frequency (678/1k Hz)
better than 226 Hz?

• better detection of middle ear effusion using
  high frequency tympanometry than using
  conventional 226 Hz tympanometry (Hunter and
  Margolis, 1992 Marchant et al, 1986 Shurin et
  al, 1976, 1977 Williams et al, 1995)
• better sensitivity to conductive pathology
  diagnosed using OAE and/or ABR (Hirsch et al,
  1992 Rhodes et al, 1999)

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2 month old with resolving OME
A. False negative at 220 Hz abnormally low
susceptance at 660 Hz B. OME resolved
A B
Shurin et al (1976)
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678 vs 1000 Hz? Keefe et al (1993)

• measured ear canal impedance and reflection
  coefficients in adults infants aged 1 to 24
  months for 125 10 700 Hz
• the frequency range from 220 to 660 Hz is the
  worst possible range to use for tympanograms on
  infants. Not only is there significant
  ear-canal wall motion, but in fact there is a
  resonant amplification of the wall motion in this
  frequency range.

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N39 clear and N13 effusion ears in 26 babies
aged 1-4 months , HFPTT versus otomicrosopy
showed substantial agreement for 1000 Hz, peak
susceptance criterion
Williams, Purdy Barber (1995)
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Tympanometric normality for HFPTT(i) based on
admittance value

• peak 660 Hz B gt 0.4 mmho (Beery et al, 1975
  Shurin et al, 1976)
• peak 660 Hz B gt 0 mmho (Marchant et al, 1986)
• mean 660 Hz B (between ?300 daPa) gt 0.16 mmho in
  infants gt 4 months (Shurin et al, 1977)
• peak 678 Hz Y (Ymax-Ymin) ? 0.12 mmho and between
  -100 and 50 daPa (Sutton et al, 1996)
• peak 1000 Hz B gt1 mmho (Williams et al, 1995)

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Tympanometric normality for HFPTT (ii) based
on tympanogram shape

• notching in the 660 Hz B tympanogram (Shurin et
  al, 1976)
• discernible B or G peak at 678 or 1000 Hz (Rhodes
  et al, 1999)
• double peaked 1000 Hz tympanogram (Thornton et
  al, 1993)
• peaked 678 Hz tympanogram with peak gt 100 daPa
  (Sutton et al, 1996)

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HFPTT tympanometric shapes associated with
effusion
129 ears of 70 children with OME history 69 ears
had effusion diagnosed via myringotomy ? 71 of
these had Class III shape
Beery et al (1975)
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Older studies using inappropriate parameters
showed poor reflex reliability in newborns, but
these still cited today unfortunately
Keith (1973, 1975), found that only one third of
healthy newborns exhibited a clear stapedial
reflex. http//audiologyonline.com
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Ipsi acoustic reflexes more reliable
McMillan et al (1985)
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Low probe tone frequencies unreliable
Weatherby Bennett (1980)
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Broadband noise stimulus recommended for tymp
cross-check

• 1000 Hz probe tone, noise stimulus 100
  detectable (n44 neonates, Weatherby Bennett,
  1980)
• Reflex threshold approx 15 dB lower for noise
  versus tone (n76 neonates, Hirsch et al, 1992)

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Recommendations for acoustic reflex testing in
infants

• Ipsilateral stimulus
• 1000 Hz probe tone frequency
• noise stimulus
• mean threshold 70 dB SPL re 2cc coupler (approx
  65 dB HL)
• std dev is about 10 dB so reflex thresholds
  exceeding 95 dB HL would be clearly abnormal

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Test protocol difficulties

• Rhodes et al (1999, p803) validated criteria
  for distinguishing normal from abnormal
  tympanograms in infants do not exist
• Hunter and Margolis currently compiling existing
  normative data for infants at 1000 Hz (L. Hunter,
  personal commun 24 Oct 2000)
• Madsen supporting research in Europe and
  Australia to validate 1000 Hz probe tone
  tympanometry in newborns (P. Morrison, personal
  commun 18 Oct 2000)

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Maturational Changes in Admittance Levels
Marchant et al (1986)
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Admittance versus Susceptance Conductance?

• van Camp et al (1976) showed that diagnosis may
  be enhanced by combining the two measures in
  adults with tm and ossicular pathology
• Conductance data not available for infants

Adult 660 Hz probe tm hypermobile
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Recommendations (1)

• low frequency probe tone tympanometry is
  unreliable and should not be used in infants
  younger than 7 months (?)
• a 1000 Hz probe tone is preferable to 660/678 Hz
• a high frequency susceptance tympanogram that has
  no discernible peak is likely to be indicative of
  effusion (but sensitivity and specificity have
  not been established)

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Recommendations (2)

• a high frequency tympanogram with low susceptance
  or admittance is likely to be indicative of
  pathology (criteria of lt0.2-1.0 have been
  suggested, but definitive data are yet to be
  established)
• the tympanogram should be cross-checked using
  reflex testing (ipsi reflex, 1000 Hz probe tone,
  broadband noise stimulus)

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2-3 mnth old infant,passed OAE screen in right
ear only
Purdy Williams (2000)