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J Am Acad Audiol 8 : 218-223 (1997)
Multifrequency Tympanometry and Evoked
Otoacoustic Emissions in Neonates during the
First 24 Hours of Life
Ann M. McKinley*'
John H. Grose*
Jackson Roush*
Abstract
Multifrequency, complex-component tympanograms and transient evoked otoacoustic emissions (EOAEs) were recorded in 55 neonates less than 24 hours of age . The purpose of the
investigation was to determine the normal middle ear immittance characteristics of neonates
less than 24 hours old (the approximate discharge age of well-babies) and to assess whether
an association exists between transient EOAE response and middle ear status in neonatal
ears .The tympanometric patterns recorded in the 55 neonates were, in general, not typical
of those observed in older children and adults . Complex patterns were recorded at low probe
frequencies indicating differences in the contribution of mass, stiffness, and resistance elements to admittance in the neonatal middle ear. Results from EOAE screening indicated a
pass rate or partial pass rate of 82 percent. Although no clear association emerged between
admittance characteristics and EOAE results, some interesting tendencies were noted .
Key Words: Evoked otoacoustic emissions (EOAEs), multifrequency tympanometry, newborn hearing screening
here is growing interest in determining
whether universal hearing screening can
Tbe cost-effectively implemented in the
hospital nursery prior to discharge, which is
typically within the first 25 hours of life (HCIA,
1994). Evoked otoacoustic emissions (EOAEs)
have been recognized by several studies as a
potentially quick, objective, and cost-effective
technique for screening newborn infants (Bonfils et al, 1988 ; Stevens et al, 1990 ; Kennedy et
al, 1991 ; Uziel and Piron, 1991 ; White et al,
1993).
The detection of EOAEs is dependent upon
the status of the auditory system peripheral to
the cochlea. EOAEs rely on normal middle ear
*Division of Speech and Hearing Sciences, The University of North Carolina at Chapel Hill, Chapel Hill, North
Carolina ; tcurrently Department of Hearing and Speech, Children's National Medical Center, Washington, DC ; $Division
of Otolaryngology-Head & Neck Surgery, The University
of North Carolina at Chapel Hill, Chapel Hill, North Carolina
Reprint requests : John H . Grose, Division of Otolaryngology-Head & Neck Surgery, CB# 7070, 610 Burnet-Womack Building, The University of North Carolina at
Chapel Hill, Chapel Hill, NC 27599-7070
function for both the transmission of the stimulus to the cochlea and for the reverse transmission of the emission to the external auditory
meatus . Therefore, it is important to assess the
status of the middle ear when using EOAEs as
a technique to screen for sensory hearing loss .
Some results have indicated that EOAE screening has low specificity when the procedure is
performed during the first postnatal day (e .g .,
Hogan and Callaghan, 1990 ; Salomon et al,
1992), although more recent reports have shown
a pass rate of over 91 percent (Maxon et al,
1995). It is possible that some EOAE failures are
due to fluid or other material temporarily
remaining in the neonatal middle ear.
Evaluation of the neonatal middle ear using
acoustic immittance measures has not been
widely performed. There is some indication that
the routine application of tympanometry using
a standard 226-Hz probe to the neonatal population is problematic because the recordings
obtained using low-frequency probe tones often
result in double-peaked susceptance, conductance, and admittance tympanograms . In normal adults and older children, single-peaked
patterns are typically recorded at this low frequency. The use of tympanometry using a low
Tympanometry and EOAEs in Neonates/McMnley et al
probe frequency is further complicated by the fact
that both normal and notched tympanograms
have been recorded in neonates with confirmed
middle ear effusion (Paradise et al, 1976 ;
Marchant et al, 1986) . These findings demonstrate the questionable validity of standard tympanometry employing low-frequency probe tones
for the detection of middle ear effusion in
neonates . The explanation for the differences
between adult and neonatal tympanograms is
not clear.
Multifrequency measures have been used to
more completely describe the tympanometric
differences seen in the neonate in comparison to
the older child. This technique allows the assessment of the relative contribution of mass,
stiffness, and resistive elements to acoustic
admittance of sound by employing multiple
probe tone frequencies (Hunter and Margolis,
1992). It has been demonstrated that multifrequency tympanometric patterns recorded in
young infants do not follow the same patterns
as in older children and adults (Himelfarb et al,
1979 ; Holte et al, 1991 ; Hirsch et al, 1992) .
From these studies, some generalizations can be
made regarding the resistive and reactive elements of the neonatal ear, assuming that the differences between neonatal tympanograms and
those of older children and adults can be attributed to the characteristics of the middle ear.
First, impedance of the neonatal middle ear is
dominated more by mass and/or resistive elements at low frequencies than is the middle ear
impedance of older infants and adults (Himelfarb et al, 1979 ; Holte et al, 1991). Consequently,
there is a downward shift to around 350 to 450
Hz in the resonant frequency of the neonatal
middle ear. Second, there is a growing contribution of stiffness elements and a decrease in the
contribution of mass elements to overall impedance during early infancy (Himelfarb et al, 1979 ;
Holte et al, 1991). This is demonstrated by an
increase in negative reactance values and admittance phase angles during the first few months
of life . Third, multifrequency tympanometric
measures suggest that significant maturational
changes take place by 2 to 4 months of age, at
which time the frequency-dependent mechanics
of the infant middle ear become more like those
of adults (Holte et al, 1991). Finally, research suggests that tympanometry using higher probe
tone frequencies (e .g ., 800 Hz) may be a better
predictor of middle ear effusion than tympanometry using standard 226-Hz probe tones
(Hirsch et al, 1992).
At the present time, there is little information available on tympanometric patterns
recorded during the first 24 hours of life . To
completely assess the condition of the neonatal
middle ear, multicomponent tympanometric
recordings are needed . This information takes
on particular significance in light of the current interest in screening cochlear function in
neonates using EOAEs.
In general, screening techniques using
EOAEs in neonates have high sensitivity (Clarkson et al, 1994); however, when EOAE measurement is performed during the first 24 hours
of life, there is often a high false-positive rate
requiring follow-up testing, which diminishes the
cost effectiveness of EOAEs as a screening device
(Kok et al, 1992). There have been several explanations for the limited specificity of EOAE testing during the first days of life . These include
reduced oxygen tension in the neonatal ear during the first 24 hours of life (Salomon et al,
1992), debris (vernix caseosa) obstructing the
external ear canal (Chang et al, 1993), and middle ear fluid, a factor that has been shown to
attenuate the EOAE response (Maxon et al,
1993). The neonatal middle ear may contain
residual amniotic fluid (Kok et al, 1992) or mesenchyme, the postnatal remnants of loose,
spongy developmental tissue known to exist in
the neonatal temporal bone (Takahara et al,
1986). Some investigators have argued that the
condition of the neonatal middle ear is not related
to the poor response rate (Salomon et al, 1992);
however, these studies employed low-frequency
probe tone tympanometry and thus may not
have been based on accurate assessment of the
middle ear in newborns .
The purpose of this investigation, therefore, was twofold. The first aim was to study
middle ear function in neonates during the first
postpartum day using multifrequency, complexcomponent tympanometric measures . The second
aim was to determine if a predictable relationship exists between the acoustic admittance
characteristics of the middle ear and the EOAE
results.
METHOD
Subjects
Subjects were 55 healthy, full-term neonates
less than 24 hours of age from the newborn
nursery at the University of North Carolina
Hospitals, Chapel Hill .
Journal of the American Academy of Audiology/ Volume 8, Number 3, June 1997
Tympanometric Measurements
Multifrequency tympanograms were
recorded unilaterally in each subject (n = 55).
Only the more accessible ear was used for testing. Complex acoustic admittance tympanograms
were recorded using probe tone frequencies of
226, 678, and 1000 Hz . Tympanograms were
recorded twice at each frequency to confirm
their reliability. All measurements were performed using a commercially available acoustic
immittance instrument (Virtual 310) . Ear canal
pressure was varied in the positive-to-negative
direction (+/-), as recommended by Holte et al
(1991) . Susceptance (B) and conductance (G)
tympanograms were obtained for analysis and
classification . Whenever possible, tympanometric shapes were classified according to the
Vanhuyse et al (1975) model. That is, each was
labeled by the number of extrema in the B and
G tympanograms . Because the neonates often
demonstrated unusual tympanometric patterns,
the category "other" was added. In addition,
tympanograms that showed no mobility were
labeled "flat." An approximation of the resonant
frequency of the middle ear was determined by
observing the probe frequency at which the susceptance "notch" dipped below the positive tail
of the B tympanogram.
EOAE Recording
EOAE testing was conducted unilaterally
prior to the tympanometric measurements . A
computer-based analyzer (Otodynamic Analyzer,
ILO88) was used to record click-evoked EOAEs
from the test ear. Babies were tested in open
bassinets in a quiet, but not sound-insulated,
room . Every effort was made to optimize probe
placement and recording conditions by (a) selecting the most appropriate probe tip size ; (b)
reseating the probe if necessary to obtain the best
apparent fit; (c) positioning the probe cord so that
it was not affected by infant movement ; (d)
adjusting test parameters (stimulus gain, noise
rejection level) as necessary; and (e) suspending
recording during periods of excessive noise.
However, no attempt was made to swab or otherwise clean the ear apart from any happenstance debris removal that occurred as a
consequence of repositioning the probe. A pass
in EOAE screening was defined as an emission
response with >_50 percent reproducibility in
three or more 1-kHz-wide frequency bands centered at 1 .0, 2.0, 3.0, 4.0, and 5.0 kHz. A partial
pass was assigned to emission responses that
220
had >_50 percent reproducibility in two frequency
bands or >_80 percent reproducibility in one frequency band . Absent or weak responses (<50%
reproducibility) were defined as a fail . Neonates
who failed the EOAE screening or received a partial pass were tested at least twice to confirm the
results.
RESULTS
ympanograms were successfully recorded
Tat 226, 678, and 1000 Hz in each subject.
Their classification, according to a modified Vanhuyse et al (1975) model, is displayed in Table
1 . With the exception of two infants, single or
multipeaked 226-Hz tympanograms were
recorded in all of the neonates . It should be
noted that in the two exceptions, estimates of
ear canal volume suggested that the flat
tympanograms were most likely due to debris
obstructing the external auditory canal rather
than to middle ear admittance characteristics.
At 678 Hz, 34 flat tympanograms were recorded .
The remaining 678-Hz tympanograms were
evenly divided between the 1B1G pattern and
the classification "other." The majority of the tympanograms recorded at 1000 Hz could not be classified according to the Vanhuyse et al (1975)
model . Most were labeled as "other" or "flat." The
remaining tympanograms recorded at 1000 Hz
were divided among the three Vanhuyse patterns. Figure 1 shows an example of the most
commonly recorded tympanometric pattern
recorded at each test frequency. An estimate of
middle ear resonance was made from the 226Hz tympanograms, which showed that 57 percent of the neonates had a middle ear resonant
frequency below 226 Hz and 43 percent had resonance above this frequency.
Screening using EOAEs was completed
immediately prior to the immittance testing.
The results indicated a pass rate of 71 percent,
a partial pass rate of 11 percent, and a fail rate
of 18 percent. Table 2 displays a breakdown of
the tympanometric patterns of the infants
according to the outcome of the EOAE screening. As the results demonstrate, no clear association emerged between tympanometric pattern
and EOAE result .
DISCUSSION
he tympanometric configurations recorded
Tin this group of newborn infants suggest
that middle ear function is different in neonates
than it is in older children and adults . Complex
Tympanometry and EOAEs in Neonates/McKinley et al
Table 1 Tympanometric Patterns for the 55
Subjects Classified According to a Modified
Vanhuyse et al (1975) Model
226 Hz
678 Hz
1000 Hz
1B1G
3B1G
3B3G
Other
Flat
0
E
E 4 .0
m
U 3.0
C
2.0
1 .0
E
a
4
3
1
-400 -300 .200 -100
29
16
0
L
tympanometric patterns were recorded at lower
probe tone frequencies than are generally
recorded in normal older children and adult
ears, suggesting differences in the relative contributions of mass, stiffness, and resistance elements to impedance for the majority of the
neonatal ears . Our results indicate that the
reactive component of the neonatal middle ear
reflects a relatively greater contribution of mass
at lower probe tone frequencies in comparison
to older children and adult ears . This is further
demonstrated by the fact that over half of the
infants had a middle ear resonant frequency
estimated to be below 226 Hz . In contrast, the
middle ear resonance of older children and adults
is estimated to be around 1000 Hz (Lilly, 1984 ;
Hunter and Margolis, 1992). Taken together,
these findings demonstrate that the neonatal ear
constitutes a different mechanical-acoustical
system than the middle ear of older children
and adults .
The validity of the 226-Hz tympanogram
in assessing middle ear status in newborns
remains questionable and controversial . It has
been suggested by some investigators that tympanometric patterns recorded at 226 Hz represent not only middle ear admittance but also
distention of the ear canal wall during pneumatization of the ear canal (Keith, 1975 ; Paradise
et al, 1976). These investigators reported that
100
200
FI
300
400
678-Hz probe frequency
4 .0
3.0
2.0
fr
.E
1 .0
a
H-~- +-H I_ ~
-400
0
.C
-300 -200 -100
300
0
5.0
E
E
400
1000-Hz probe frequency
4 .0
3 .0
U
C
cC
2.0
E 1 .0
Q
-400 -300 -200
Ga
ea:
0
0
100
200
300
400
Air pressure (daPa)
Figure 1 Examples of the most commonly recorded
tympanograms at each test frequency. At 226 Hz, the
3B3G was the most typical tympanometric pattern; at 678
Hz, the majority of tympanograms were classified as
flat ; and at 1000 Hz, most of the tympanograms were classified as "other."
pressurizing the neonatal ear canal during tympanometry may cause distention of the incompletely ossified ear canal walls. They speculated
that movement of the ear canal walls may result
in peaked tympanograms . Other reports (Holte
et al, 1991) have brought into question the contribution of external canal wall movement to
tympanometric shape recorded at 226 Hz . Keefe
et al (1993) have determined that the measurement of the input impedance of an infant ear is
Tympanometric Patterns Recorded at Each Test Frequency According to EOAE Response
Classification : Pass, Partial Pass (P/Pass), Fail
1000 Hz
678 Hz
226 Hz
1B1G
3B1G
383G
Other
Flat
0
5.0
E
_E
N
U
C
Table 2
226-Hz probe frequency
5.0
L
Pass
P/Pass
Fail
7
5
27
0
0
2
4
0
0
0
1
3
4
0
2
Pass
8
0
0
10
21
P/Pass
Fail
Pass
P/Pass
Fail
2
0
0
0
4
0
0
0
0
9
3
2
1
25
7
1
0
0
2
3
0
1
0
2
6
Journal of the American Academy of Audiology/Volume 8, Number 3, June 1997
strongly affected by motion and resonance of
the ear canal wall for frequencies below about
660 Hz . They recommend higher frequency probe
tones, above 660 Hz, for the assessment of middle ear function in neonates .
Successful implementation of a universal
screening program ideally involves testing prior
to hospital discharge, which typically occurs
within the first 24 hours of life . In the current
study, 29 percent of the subjects screened during the first postnatal day received either a partial pass or fail and required follow-up testing.
Although other investigators have reported a
substantially higher pass rate (e .g ., Maxon et al,
1995), others have reported similar outcomes
(Kok et al, 1992 ; Salomon et al, 1992 ; Salamy et
al, 1996).
No clear association emerged between EOAE
results and middle ear admittance characteristics observed tympanometrically, possibly due in
part to the relatively small number of ears
tested . Although a clear association between
EOAE results and tympanometric patterns is not
apparent from these data, some possible tendencies emerged. For example, all babies who
failed the emission screening had flat 678-Hz
tympanograms, whereas several of the infants
who had recordable EOAEs had peaked tympanograms at this frequency. This demonstrates
that at 678 Hz, none of the infants who failed
emissions showed any apparent admittance
change with variation of air pressure, whereas
a proportion of the babies with measurable
EOAEs did exhibit such change .
Because multicomponent tympanometric
measures have not been widely performed in
neonates, a model for classifying the variety of
tympanometric patterns recorded in this population has not been developed. The Vanhuyse et
al (1975) model has been used by some investigators to categorize multicomponent tympanograms in older children and adults, but it
is not adequate for classifying and interpreting
many neonatal tympanograms . In order to use
tympanometry to assess the status of the middle ear in newborns, additional research is
needed to develop a model for classifying and
interpreting the patterns recorded in this population. Recording of acoustic reflexes might
aid in the interpretation of neonatal tympanograms and help determine the clinical value
of acoustic immittance measures in this population .
In summary, this study has demonstrated
that the transmission characteristics of the
neonatal middle and outer ears are likely to dif222
fer from those of older children and adults .
Assessment of middle ear function in conjunction with otoacoustic emissions may lead to a better understanding of why some neonates with
apparently normal cochlear function initially
fail EOAE screening. Additional research is
needed to further describe, classify, and interpret the immittance characteristics of the neonatal ear.
This paper was presented at the
Acknowledgment .
Annual Convention of the North Carolina Speech Hearing and Language Association, April 1995 .
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