HEARING TESTING
Auditory Screening of Preschool Children with Impedance Audiometry—A Comparison with Pure Tone Audiometry Detecting Otologic Disease Prior John A.
to the Onset of
Hearing Loss
McCurdy, Jr., M.D., Jerod L. Goldstein, Ph.D., David Gorski, B.A.
THE
ADVERSE EFFECT of mild hearing impairment in early childhood on the acquisi-
child, high ambient noise levels in the school testing environment, faulty calibration of
tion of verbal skills has been well documented .1-3 Manly children with mild impairment are otherwise asymptomatic, and thus their parents and teachers are unaware of their otologic abnormality. An effective otologic screening program offers the best method of identifying such mild hearing impairments, enabling early management of these disorders. Auditory screening with conventional pure tone audiometry has proven to be of low sensitivity in the early detection of middle ear disorders in young children. In the comprehensive survey of Eagles, et al.,4,5 nearly twothirds of children with an abnormal otologic examination were not identified by pure tone audiometry. The reasons for this unsatisfac-
audiometric equipment, and the subjective nature of the test itself. Furthermore, the data of Cohen and Sad66 indicate that a significant percentage of children with secretory otitis media, the most common cause of mild hearing loss in childhood, demonstrate normal hearing threshold levels when tested
tory
performance are cdoperation on
lack of
From
the
numerous,
including
the part of the young
Otolaryngology
and
Clinical Research
Services, Madigan Army Medical Center, Tacoma, Wash. 98498.
Correspondence Box 572, Madigan Wash. 98431.
John A. McCurdy, Jr., M.D., Army Medical Center, Tacoma,
to
by
pure
tone
audiometry.
Hence, for the early detection and ment
of young children with
treat-
otologic
dis-
orders, screening techniques more sensitive than conventional pure tone audiometry are
required. The development of acoustic impedance measurements has provided an expeditious, reliable and objective method for the early detection of otologic disorders of childhood.’ This technique has been shown to be effective in the identification of middle ear abnormalities in school children, correlating well with the results of otoscopic examination.gps In this report, we have compared the results of conventional pure tone screening with those of impedance audiometry in a population of preschool children (aged 3 V2 to 4
years).
436
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
FIG. 1. Schematic representation of the electroacoustic impedance bridge. with permission from Otoadmittance Handbook 2, Grason-Stadler Co., Concord, ~Iass.,
(Reproduced
1973.)
Basic Considerations
vary the pressure in the external canal from +200 to -400 mm H20. As the pressure in the external canal is varied, the acoustic impedance of the tympanic membrane changes simultaneously, resulting in altered sound pressure levels in the external canal. These levels are monitored by the microphone and relayed to a balance meter on which the changes are portrayed in units of acoustic impedance. Plotting the changes in impedance or its
one to
Resistance to the transmission of sound is termed &dquo;acoustic impedance.&dquo; When sound waves strike the tympanic membrane, a portion of the acoustic energy is transmitted and the remainder, determined by the acoustic impedance of the drumhead and ossicular chain, is reflected. When the total acoustic energy impinging on the tympanic membrane is known, measurement of the reflected energy enables one to calculate the acoustic impedance of the middle ear. 10 &dquo;Tympanometry,&dquo; one component of the impedance battery, is based on the principle that the transmission of sound by the middle ear is greatest (lowest acoustic impedance) when the pressure on both sides of the tympanic membrane is equal. Thus, by systematically varying the pressure in the external auditory canal, one can determine the middle ear pressure by noting the pressure at which the acoustic impedance is lowest. As the major function of the eustachian tube is ventilation of the tympanic cavity and equalization of middle ear pressure with the ambient pressure, this measurement is a sensitive indicator of tubal function. To perform tympanometry, a small &dquo;probe tip&dquo; is carefully fitted into the external auditory canal in order to form an air tight seal (Fig. 1). This probe tip contains three small tubes, one of which transmits a probe tone of 220 Hz of a known sound pressure level. The second tube communicates with a microphone which monitors the sound pressure level in the external canal (i.e., sound reflected from the tympanic membrane). The third tube is connected to a pressure pump which allows
reciprocal (compliance) generates a tympanogram. The peak of the tympanogram, or point of minimum impedance (maximum compliance) corresponds to the middle ear pressure. The three major types of tympanograms are illustrated in Figure 2. The normal middle maintains a pressure near ambient levels and is characterized by a tympanogram with a sharp peak near zero on the pressure axis (type A). Eustachian tube dysfunction impairs middle ear ventilation, resulting in a partial vacuum (negative pressure) in the tympanic cavity. Negative pressure of -100 mm H~O or below produces a type C tympanogram. Middle ear effusion generally produces a flat type B tympanogram with no discernable peak or a type C curve with a high negative middle ear pressure. 11,12 Kith 13 noted that ears with negative pressures below - 150 mm H20 are likely to demonstrate effusion. The stapedius reflex can be measured by applying sound of a given frequency to the contralateral ear. This reflex arc is bilateral, both stapedius muscles contracting in response to an appropriate stimulus. The contraction results in a change in the acoustic impedance of the test (probe) ear which is detected on ear
437
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
Ftc. 2. Classification of
tympanograms. The type A tympanogram is obtained with normal middle The type B tympanogram is highly suggestive of middle ear effusion. The type C tympanogram indicates negative middle ear pressure of -100 mm H~!~ or below, with or without middle ear effusion. ears.
the balance meter of the impedance bridge. This reflex is a sensitive indicator of middle ear
function.
Thus, impedance audiometry provides
a
direct measurement of middle ear function rather than of hearing levels per se. In this respect, it is important to reiterate the observation that a significant percentage of the children with abnormal middle ear function show normal hearing on pure tone screening audiometry.’ Early identification of such subclinical abnormalities allows initiation of appropriate treatment and follow-up, hopefully preventing the development of hearing loss and other sequelae of eustachian tube dysfunction such as recurrent acute suppurative otitis media, adhesive otitis media, cholesteatoma, tympanosclerosis, ossicular discontinuity, and cholesterol granuloma (idio-
pathic hemotympanum). Original
Observations
We tested 93 children
(186 ears) aged
four years enrolled in a community preschool, both by conventional pure tone
3Y2
to
screening audiometry and an impedance battery consisting of tympanometry and acoustic reflex measurement at 1000 Hz. All tests were conducted in a vacant classroom. Pure
tone
screening
was
performed
at a
hearing threshold level of 25 dB ISO for the of 500, 1,000, 2,000, and 4,000 Hz, using a Beltone 10A audiometer. The criterion for failure was lack of response to any two of these four frequencies. Tympanometry and measurement of the stapedius reflex thresholds at 1,000 Hz was performed using a Madsen ZO-70 ElectroAcoustic Impedance Bridge. The criteria for failure were a tympanogram of type B or C,
frequencies
or a
type A tympanogram with absence of the
stapedius reflex. Impedance measurements
obtainable with pure tone audiometry. Failure was related to inability to obtain an adequate external canal seal (14 ears), or the presence of a tym-. panostomy tube (three ears) as treatment for secretory otitis media. The results of pure tone and impedance screening are tabulated in Figure 3. in 169 of the 186
ears
were
(90.9%) screened
Twenty-four ears (12.9%) passed pure tone screening but demonstrated middle ear abnormalities on impedance testing. Eighteen (9.7%) of these ears showed type C tympanograms and six (3.2%) had type B tympanograms. No ear failed on the basis of a type A tympanogram with an absent stapedius reflex. This 12.9 per cent incidence of children with middle ear conditions not detected by pure tone screening is in good agreement with the results of Harker and Von Wagoner8 who found impedance measurements detected abnormalities in 9.7 per cent of a population composed of both preschool and grade school children passing pure tone screening. In contrast, 43 ears (~3.1°~~) failing pure tone screening demonstrated normal middle ear function on impedance testing (type A tympanogram with normal stapedius reflex. thresholds). On follow-up examination, all of these ears showed normal hearing by pure tone threshold audiometry. This 23.1 per cent incidence of false positive detection by pure tone screening is comparable to the 22.5 per cent false positive rate reported by Kohler and Horst’ in their series of pure tone screening in four-year-old children. The overall failure rate for impedance
438
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
FIG. 3. Results of im-
pedance and pure tone audiometry. Impedance measurements
were
un-
successful in 17 of 186 ears studied (9.1 %). All patients with type A tympanograms showed normal stapedius reflex thresholds.
audiometry per
cent
in the 169
(81 ears),
a
tested was 47.9 C type tympanogram ears
being found in 58 ears (34.3%) and a type B tympanogram in- 23 ears (13.6%). Relationships between these impedance failures and performance on pure tone screening are shown in Table 1. These results suggest that
exhibiting type C tympanograms are likely to fail pure tone screening as the degree of negative middle ear pressure increases, possibly reflecting an increasing probability of middle ear effusion with increasing negative pressure in the tympanic space. 13 ears
more
in which 61 per cent of otoscopic abnormal children were not detected by pure tone screening, convincingly demonstrates that many children with otologic disorders will escape identification by conventional audiometry alone. This finding has been confirmed by McCandless and Thomas9 who, in an auditory screening program, found the agreement between pure tone audiometry and otoscopy to be only 60 per cent in children aged three to five years. The measurement of acoustic impedance theoretically constitutes the most accurate method presently available TABLE 1. Results
of Pure Tone Screening in Impedance Audiometry Failures
Comments and Discussion failure rate for impedance audiin this ometry group of preschool subjects is a manifestation of the high incidence of middle ear abnormalities secondary to eustachian tube dysfunction in young children. Both anatomic peculiarities of the immature eustachian tube and the high incidence of upper respiratory infections in this age group contribute to this appreciable incidence of tubal dysfunction. Brooks’2 has shown that the incidence of middle ear abnormalities found with impedance testing decreases sharply with
The
high
increasing age.
81 ears) Forty-eight of these ears failed pure tone while 33 passed. The incidence of failure in children with type C tympanograms increased as a function of increasing negative middle ear pressure (see test). The incidence of failure was highest in children with type B tympanograms.
(N
The aim of auditory screening should be the detection of otologic disease in its early stages, preferably prior to the onset of hearing loss. The investigations of Eagles, et al., 4,5
=
screening
439
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
for identification of middle ear dysfunction. investigations have demonstrated the correlation between impedance measureRecent
and otoscopy performed by an otologist be in the range of 90 to 100 per cent.9 Since impedance audiometry measures middle ear function rather than hearing per se, screening with this method alone will not detect sensorineural hearing impairment. The incidence, however, of previously undetected sensorineural hearing loss in young children is extremely low (0.2%).*~ Most children (70%) failing impedance screening demonstrate type C tympanograms, indicative of middle ear pressure - 100 mm H20 or below. Even in the absence of frank effusion, children with high negative middle ear pressures should be considered at otologic risk since this finding indicates a dysfunction of the eustachian tube, generally considered to be the precursor of middle ear effusion (secretory otitis media) as well as acute and chronic suppurative otitis media. A significant percentage of children with type C tympanograms subsequently develop type B curves.8 In contrast to the high incidence of false positive results in pure tone screening (20 to 25%), the false positive rate with impedance screening is estimated to be 4 to 6 per cent.9 A further advantage of impedance audiometry is its simplicity. This procedure is easily performed by nontechnical personnel. It is completely objective, no patient response being required-an obvious advantage in testing preschool children. The validity of the procedure is not affected by ambient noise which is frequently excessive in areas in which pure tone screening is performed. In addition, satisfactory tests can be performed on 7 over 90 per cent of young children.7 ments to
,
*
It is estimated that
1
in 2,000 children have
profound congenital sensorineural hearing loss. 14 These children are identified prior to entry into preschool programs and thus would not be included in school audiometric screening programs. It has been suggested that sensorineural losses can be detected with the use of a single screening pure tone of 4,000 HZ at 25 dB HTL ISO.’
Final Comments
Impedance audiometry constitutes an efficient, reliable, and objective method for detection of clinical and subclinical otologic disease in childhood. It will detect middle ear abnormalities in a significant percentage of children who pass pure tone screening. Its use in school screening programs reduces the incidence of false positive referrals as compared with pure tone screening. If the goal of auditory screening is the detection of otologic disease rather than hearing loss per se, impedance audiometry would seem to constitute an ideal screening method, particularly in a population of young school children in whom mild hearing impairment is largely conductive in nature and thus amenable to appropriate therapy. Addendum Electroacoustic impedance bridges are distributed in the United States by several manufacturers. Two of these companies, American Electromedics and Grason-Stadler, offer regularly scheduled courses of instruction in the theory and practical application of impedance audiometry. These courses are conducted at various locations throughout the country and are designed specifically for physicians and paramedical personnel with no previous experience in this field.
References 1.
Holm, V. A., and Kunze, L. H.: Effect of chronic
otitis media on language and speech development. Pediatrics 43: 833, 1969. 2. Kohler, L., and Holst, H.: Auditory screening of four-year-old children. Acta. Paediatr. Scand.
61: 555, 1972. 3.
G. J., Fleshman, J. K., Bender, T. R., Baum, C., and Clark, P. S.: Long-term effects of
Kaplan,
otitis media—a ten-year cohort study of Alaskan Eskimo children. Pediatrics 52: 577, 1973. 4. Eagles, E. L., Wishik, S. M., and Doerfler, L. G.: Hearing sensitivity and ear disease in children: a prospective study. Laryngoscope Suppl., 1967. 5. —: A longitudinal study of ear disease and hearing sensitivity in children. Audiology 12:
438, 1973. 6. Cohen, D., and Sadé, J.: Hearing in secretory otitis media. Can. J. Otol. 1: 27, 1972. 7. Jerger, S., Jerger, J., Mauldin, L., and Segal, P.:
440
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
8.
9.
10. 11.
Studies in impedance audiometry. Children less than six years old. Arch. Otolaryngol. 99: 1, 1974. Harker, L. A., and Van Wagoner, R.: Application of impedance audiometry as a screening instrument. Acta Otolaryngol. 77: 198, 1974. McCandless, G. A., and Thomas, G. K.: Impedance audiometry as a screening procedure for middle ear disease. Trans. Am. Acad. Opthmol. Otolaryngol. 78: 98, 1974. Jerger, J.: Clinical experience with impedance audiometry. Arch. Otolaryngol. 92: 311, 1970. Bluestone, C. D., Beery, Q. C., and Paradise,
L.: Audiometry and tympanometry in relation middle ear effusions in children. Laryngoscope 84: 594, 1974. 12. Brooks, D. N.: The use of the electroacoustic impedance bridge in the assessment of middle ear function. J. Int. Audiol. 8: 563, 1969. 13. Keith, R. W.: Applications of impedance audiometry with children. Hearing Instruments 25:
J.
to
18, 1974. 14. Proctor, C. A., and Proctor, B.: Understanding hereditary nerve deafness. Arch Otolaryngol.
85: 45, 1967.
441
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
Auditory Screening of Preschool Children with Impedance Audiometry—A Comparison with Pure Tone Audiometry Detecting Otologic Disease Prior John A.
to the Onset of
Hearing Loss
McCurdy, Jr., M.D., Jerod L. Goldstein, Ph.D., David Gorski, B.A.
THE
ADVERSE EFFECT of mild hearing impairment in early childhood on the acquisi-
child, high ambient noise levels in the school testing environment, faulty calibration of
tion of verbal skills has been well documented .1-3 Manly children with mild impairment are otherwise asymptomatic, and thus their parents and teachers are unaware of their otologic abnormality. An effective otologic screening program offers the best method of identifying such mild hearing impairments, enabling early management of these disorders. Auditory screening with conventional pure tone audiometry has proven to be of low sensitivity in the early detection of middle ear disorders in young children. In the comprehensive survey of Eagles, et al.,4,5 nearly twothirds of children with an abnormal otologic examination were not identified by pure tone audiometry. The reasons for this unsatisfac-
audiometric equipment, and the subjective nature of the test itself. Furthermore, the data of Cohen and Sad66 indicate that a significant percentage of children with secretory otitis media, the most common cause of mild hearing loss in childhood, demonstrate normal hearing threshold levels when tested
tory
performance are cdoperation on
lack of
From
the
numerous,
including
the part of the young
Otolaryngology
and
Clinical Research
Services, Madigan Army Medical Center, Tacoma, Wash. 98498.
Correspondence Box 572, Madigan Wash. 98431.
John A. McCurdy, Jr., M.D., Army Medical Center, Tacoma,
to
by
pure
tone
audiometry.
Hence, for the early detection and ment
of young children with
treat-
otologic
dis-
orders, screening techniques more sensitive than conventional pure tone audiometry are
required. The development of acoustic impedance measurements has provided an expeditious, reliable and objective method for the early detection of otologic disorders of childhood.’ This technique has been shown to be effective in the identification of middle ear abnormalities in school children, correlating well with the results of otoscopic examination.gps In this report, we have compared the results of conventional pure tone screening with those of impedance audiometry in a population of preschool children (aged 3 V2 to 4
years).
436
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
FIG. 1. Schematic representation of the electroacoustic impedance bridge. with permission from Otoadmittance Handbook 2, Grason-Stadler Co., Concord, ~Iass.,
(Reproduced
1973.)
Basic Considerations
vary the pressure in the external canal from +200 to -400 mm H20. As the pressure in the external canal is varied, the acoustic impedance of the tympanic membrane changes simultaneously, resulting in altered sound pressure levels in the external canal. These levels are monitored by the microphone and relayed to a balance meter on which the changes are portrayed in units of acoustic impedance. Plotting the changes in impedance or its
one to
Resistance to the transmission of sound is termed &dquo;acoustic impedance.&dquo; When sound waves strike the tympanic membrane, a portion of the acoustic energy is transmitted and the remainder, determined by the acoustic impedance of the drumhead and ossicular chain, is reflected. When the total acoustic energy impinging on the tympanic membrane is known, measurement of the reflected energy enables one to calculate the acoustic impedance of the middle ear. 10 &dquo;Tympanometry,&dquo; one component of the impedance battery, is based on the principle that the transmission of sound by the middle ear is greatest (lowest acoustic impedance) when the pressure on both sides of the tympanic membrane is equal. Thus, by systematically varying the pressure in the external auditory canal, one can determine the middle ear pressure by noting the pressure at which the acoustic impedance is lowest. As the major function of the eustachian tube is ventilation of the tympanic cavity and equalization of middle ear pressure with the ambient pressure, this measurement is a sensitive indicator of tubal function. To perform tympanometry, a small &dquo;probe tip&dquo; is carefully fitted into the external auditory canal in order to form an air tight seal (Fig. 1). This probe tip contains three small tubes, one of which transmits a probe tone of 220 Hz of a known sound pressure level. The second tube communicates with a microphone which monitors the sound pressure level in the external canal (i.e., sound reflected from the tympanic membrane). The third tube is connected to a pressure pump which allows
reciprocal (compliance) generates a tympanogram. The peak of the tympanogram, or point of minimum impedance (maximum compliance) corresponds to the middle ear pressure. The three major types of tympanograms are illustrated in Figure 2. The normal middle maintains a pressure near ambient levels and is characterized by a tympanogram with a sharp peak near zero on the pressure axis (type A). Eustachian tube dysfunction impairs middle ear ventilation, resulting in a partial vacuum (negative pressure) in the tympanic cavity. Negative pressure of -100 mm H~O or below produces a type C tympanogram. Middle ear effusion generally produces a flat type B tympanogram with no discernable peak or a type C curve with a high negative middle ear pressure. 11,12 Kith 13 noted that ears with negative pressures below - 150 mm H20 are likely to demonstrate effusion. The stapedius reflex can be measured by applying sound of a given frequency to the contralateral ear. This reflex arc is bilateral, both stapedius muscles contracting in response to an appropriate stimulus. The contraction results in a change in the acoustic impedance of the test (probe) ear which is detected on ear
437
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
Ftc. 2. Classification of
tympanograms. The type A tympanogram is obtained with normal middle The type B tympanogram is highly suggestive of middle ear effusion. The type C tympanogram indicates negative middle ear pressure of -100 mm H~!~ or below, with or without middle ear effusion. ears.
the balance meter of the impedance bridge. This reflex is a sensitive indicator of middle ear
function.
Thus, impedance audiometry provides
a
direct measurement of middle ear function rather than of hearing levels per se. In this respect, it is important to reiterate the observation that a significant percentage of the children with abnormal middle ear function show normal hearing on pure tone screening audiometry.’ Early identification of such subclinical abnormalities allows initiation of appropriate treatment and follow-up, hopefully preventing the development of hearing loss and other sequelae of eustachian tube dysfunction such as recurrent acute suppurative otitis media, adhesive otitis media, cholesteatoma, tympanosclerosis, ossicular discontinuity, and cholesterol granuloma (idio-
pathic hemotympanum). Original
Observations
We tested 93 children
(186 ears) aged
four years enrolled in a community preschool, both by conventional pure tone
3Y2
to
screening audiometry and an impedance battery consisting of tympanometry and acoustic reflex measurement at 1000 Hz. All tests were conducted in a vacant classroom. Pure
tone
screening
was
performed
at a
hearing threshold level of 25 dB ISO for the of 500, 1,000, 2,000, and 4,000 Hz, using a Beltone 10A audiometer. The criterion for failure was lack of response to any two of these four frequencies. Tympanometry and measurement of the stapedius reflex thresholds at 1,000 Hz was performed using a Madsen ZO-70 ElectroAcoustic Impedance Bridge. The criteria for failure were a tympanogram of type B or C,
frequencies
or a
type A tympanogram with absence of the
stapedius reflex. Impedance measurements
obtainable with pure tone audiometry. Failure was related to inability to obtain an adequate external canal seal (14 ears), or the presence of a tym-. panostomy tube (three ears) as treatment for secretory otitis media. The results of pure tone and impedance screening are tabulated in Figure 3. in 169 of the 186
ears
were
(90.9%) screened
Twenty-four ears (12.9%) passed pure tone screening but demonstrated middle ear abnormalities on impedance testing. Eighteen (9.7%) of these ears showed type C tympanograms and six (3.2%) had type B tympanograms. No ear failed on the basis of a type A tympanogram with an absent stapedius reflex. This 12.9 per cent incidence of children with middle ear conditions not detected by pure tone screening is in good agreement with the results of Harker and Von Wagoner8 who found impedance measurements detected abnormalities in 9.7 per cent of a population composed of both preschool and grade school children passing pure tone screening. In contrast, 43 ears (~3.1°~~) failing pure tone screening demonstrated normal middle ear function on impedance testing (type A tympanogram with normal stapedius reflex. thresholds). On follow-up examination, all of these ears showed normal hearing by pure tone threshold audiometry. This 23.1 per cent incidence of false positive detection by pure tone screening is comparable to the 22.5 per cent false positive rate reported by Kohler and Horst’ in their series of pure tone screening in four-year-old children. The overall failure rate for impedance
438
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
FIG. 3. Results of im-
pedance and pure tone audiometry. Impedance measurements
were
un-
successful in 17 of 186 ears studied (9.1 %). All patients with type A tympanograms showed normal stapedius reflex thresholds.
audiometry per
cent
in the 169
(81 ears),
a
tested was 47.9 C type tympanogram ears
being found in 58 ears (34.3%) and a type B tympanogram in- 23 ears (13.6%). Relationships between these impedance failures and performance on pure tone screening are shown in Table 1. These results suggest that
exhibiting type C tympanograms are likely to fail pure tone screening as the degree of negative middle ear pressure increases, possibly reflecting an increasing probability of middle ear effusion with increasing negative pressure in the tympanic space. 13 ears
more
in which 61 per cent of otoscopic abnormal children were not detected by pure tone screening, convincingly demonstrates that many children with otologic disorders will escape identification by conventional audiometry alone. This finding has been confirmed by McCandless and Thomas9 who, in an auditory screening program, found the agreement between pure tone audiometry and otoscopy to be only 60 per cent in children aged three to five years. The measurement of acoustic impedance theoretically constitutes the most accurate method presently available TABLE 1. Results
of Pure Tone Screening in Impedance Audiometry Failures
Comments and Discussion failure rate for impedance audiin this ometry group of preschool subjects is a manifestation of the high incidence of middle ear abnormalities secondary to eustachian tube dysfunction in young children. Both anatomic peculiarities of the immature eustachian tube and the high incidence of upper respiratory infections in this age group contribute to this appreciable incidence of tubal dysfunction. Brooks’2 has shown that the incidence of middle ear abnormalities found with impedance testing decreases sharply with
The
high
increasing age.
81 ears) Forty-eight of these ears failed pure tone while 33 passed. The incidence of failure in children with type C tympanograms increased as a function of increasing negative middle ear pressure (see test). The incidence of failure was highest in children with type B tympanograms.
(N
The aim of auditory screening should be the detection of otologic disease in its early stages, preferably prior to the onset of hearing loss. The investigations of Eagles, et al., 4,5
=
screening
439
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
for identification of middle ear dysfunction. investigations have demonstrated the correlation between impedance measureRecent
and otoscopy performed by an otologist be in the range of 90 to 100 per cent.9 Since impedance audiometry measures middle ear function rather than hearing per se, screening with this method alone will not detect sensorineural hearing impairment. The incidence, however, of previously undetected sensorineural hearing loss in young children is extremely low (0.2%).*~ Most children (70%) failing impedance screening demonstrate type C tympanograms, indicative of middle ear pressure - 100 mm H20 or below. Even in the absence of frank effusion, children with high negative middle ear pressures should be considered at otologic risk since this finding indicates a dysfunction of the eustachian tube, generally considered to be the precursor of middle ear effusion (secretory otitis media) as well as acute and chronic suppurative otitis media. A significant percentage of children with type C tympanograms subsequently develop type B curves.8 In contrast to the high incidence of false positive results in pure tone screening (20 to 25%), the false positive rate with impedance screening is estimated to be 4 to 6 per cent.9 A further advantage of impedance audiometry is its simplicity. This procedure is easily performed by nontechnical personnel. It is completely objective, no patient response being required-an obvious advantage in testing preschool children. The validity of the procedure is not affected by ambient noise which is frequently excessive in areas in which pure tone screening is performed. In addition, satisfactory tests can be performed on 7 over 90 per cent of young children.7 ments to
,
*
It is estimated that
1
in 2,000 children have
profound congenital sensorineural hearing loss. 14 These children are identified prior to entry into preschool programs and thus would not be included in school audiometric screening programs. It has been suggested that sensorineural losses can be detected with the use of a single screening pure tone of 4,000 HZ at 25 dB HTL ISO.’
Final Comments
Impedance audiometry constitutes an efficient, reliable, and objective method for detection of clinical and subclinical otologic disease in childhood. It will detect middle ear abnormalities in a significant percentage of children who pass pure tone screening. Its use in school screening programs reduces the incidence of false positive referrals as compared with pure tone screening. If the goal of auditory screening is the detection of otologic disease rather than hearing loss per se, impedance audiometry would seem to constitute an ideal screening method, particularly in a population of young school children in whom mild hearing impairment is largely conductive in nature and thus amenable to appropriate therapy. Addendum Electroacoustic impedance bridges are distributed in the United States by several manufacturers. Two of these companies, American Electromedics and Grason-Stadler, offer regularly scheduled courses of instruction in the theory and practical application of impedance audiometry. These courses are conducted at various locations throughout the country and are designed specifically for physicians and paramedical personnel with no previous experience in this field.
References 1.
Holm, V. A., and Kunze, L. H.: Effect of chronic
otitis media on language and speech development. Pediatrics 43: 833, 1969. 2. Kohler, L., and Holst, H.: Auditory screening of four-year-old children. Acta. Paediatr. Scand.
61: 555, 1972. 3.
G. J., Fleshman, J. K., Bender, T. R., Baum, C., and Clark, P. S.: Long-term effects of
Kaplan,
otitis media—a ten-year cohort study of Alaskan Eskimo children. Pediatrics 52: 577, 1973. 4. Eagles, E. L., Wishik, S. M., and Doerfler, L. G.: Hearing sensitivity and ear disease in children: a prospective study. Laryngoscope Suppl., 1967. 5. —: A longitudinal study of ear disease and hearing sensitivity in children. Audiology 12:
438, 1973. 6. Cohen, D., and Sadé, J.: Hearing in secretory otitis media. Can. J. Otol. 1: 27, 1972. 7. Jerger, S., Jerger, J., Mauldin, L., and Segal, P.:
440
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
8.
9.
10. 11.
Studies in impedance audiometry. Children less than six years old. Arch. Otolaryngol. 99: 1, 1974. Harker, L. A., and Van Wagoner, R.: Application of impedance audiometry as a screening instrument. Acta Otolaryngol. 77: 198, 1974. McCandless, G. A., and Thomas, G. K.: Impedance audiometry as a screening procedure for middle ear disease. Trans. Am. Acad. Opthmol. Otolaryngol. 78: 98, 1974. Jerger, J.: Clinical experience with impedance audiometry. Arch. Otolaryngol. 92: 311, 1970. Bluestone, C. D., Beery, Q. C., and Paradise,
L.: Audiometry and tympanometry in relation middle ear effusions in children. Laryngoscope 84: 594, 1974. 12. Brooks, D. N.: The use of the electroacoustic impedance bridge in the assessment of middle ear function. J. Int. Audiol. 8: 563, 1969. 13. Keith, R. W.: Applications of impedance audiometry with children. Hearing Instruments 25:
J.
to
18, 1974. 14. Proctor, C. A., and Proctor, B.: Understanding hereditary nerve deafness. Arch Otolaryngol.
85: 45, 1967.
441
Downloaded from cpj.sagepub.com at FUDAN UNIV LIB on May 5, 2015
