Advanced Techniques for Measuring Middle Ear Function

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Advanced

Techniques

for Measuring

Middle

Ear

Function

Jerry L Northern, Ph.D.

From the Departments of Otolaryngology/Pediatrics, University of COlOrado Medical Center, and the Audiology Division, Colorado General Hospital, Denver

The use of acoustic impedance measurement as

a means of evaluating the physiological function

of the middle ear system is gaining wide interest

by

pediatricians.’3 The impedance technique is

extremely sensitive to differentiating between

normal and pathological middle ears.

Children with middle ear effusions are

typi-cally identified by physicians through an

otoscop-ic examination, or by audiologists when the child

fails

the traditional hearing screening test at

school. Most physicians use otoscopy to visually

examine the tympanic membrane, but with

varying

degrees of success.4 Otologists teach that

pneumatic otoscopy is an absolute necessity to

identify the presence of middle ear disease, yet

only 25% of physicians

use

the pneumatic

oto-scope.5 In a recent study of the accuracy of

otoscopic diagnoses, 15% to 20% of ears in

chil-dren under 3 years of age with effusions were

missed clinically.

This

high miss rate was noted in

a group of examiners from a medical center who

were aware that their diagnostic skill was being

evaluated and

thus

should have been motivated to

perform their most careful otoscopy.6 Accurate

otoscopy and pneumotoscopy require skilled and

experienced individuals. Our experience in

train-ing health professionals shows considerable

van-ability in interpretation of otoscopic observations.

Other problems in otoscopy include difficulty in

visualizing the tympanic membrane, the removal

of cerumen prior to examination, and the

unwill-ingness of some children to cooperate with the

examination.

not necessary to determine accurate

tympanom-etny

measurements,

thereby eliminating the need

to remove cerumen from every patient’s ear.

Tympanometry

is defined as an objective

tech-mque for measuring the compliance (or mobility)

of the

tympanic

membrane and middle ear

system. This compliance measurement is

deter-mined at specific air

pressures

created in a

hermatically sealed external ear canal.

Con-ceptually,

tympanometry

may be considered a

technique of “electronic pneumatic otoscopy.”

The compliance of the tympanic membrane is of

particular

clinical significance, since almost any

pathological condition involving

the

eardrum or

middle

ear

cavity

will influence the mobility of

the tympanic membrane. Tympanometry utilizes

smaller air pressure changes ( +

200

to

-400

mm

H,O

relative to atmospheric

air

pressure) than

typically

created when performing pneumatic

otoscopy.

It

is not uncommon in manual

pneu-matic

otoscopy for the clinician to use

air

pres-sures of

±800

to 1,000 mm H,O.

Tympanometry

provides an indirect, but

extremely

precise, measure of existing middle ear

pressure. This is accomplished by determining the

ear canal air pressure at which the tympanic

membrane is most compliant, which occurs when

the external ear canal air pressure equals the

patient’s

middle

ear pressure (Fig. 1). Patients

who have intact tympanic membranes, normal

middle

ear

function,

and

adequate Eustachian

tube

aeration show tympamc membrane

maxi-mum

compliance at atmospheric air pressure.

TYMPANOMETRY

Tympanometry resolves many of the

disadvan-tages of conventional audiology and otologic

assessment. It requires only passive cooperation

from children since no overt response is required.

Total visualization of the tympanic membrane is

Read in part before the American Academy of Pediatrics Section on Allergy, Chicago, October 18, 1976.

ADDRESS FOR REPRINTS: (J.LN.) Box B210, 4200 East

(2)

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FIG. 1. Compliance of tympanic membrane is at its maximum when air pressure in external ear canal is equal to air pressure of middle ear space. Thus, tympanometry can be

used to measure existing middle ear air pressure.

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- AIR PRESSURE

Accurate measurement of middle ear pressure

may provide significant clinical information

rela-tive to otitis media. When the process of aeration

in the middle ear is halted, as in closure of the

Eustachian tube, the now static air in the middle

ear space is absorbed by the blood vessels in the

mucosal lining. This situation produces negative

air pressure in the middle ear space causing

transudation of fluid and retraction of the

tympanic membrane. If the aeration process of the middle ear cavity is blocked, fluid may fill the

middle ear space. Thus, the early identification of

negative middle ear pressure may permit the

physician to practice preventive medicine and

avoid middle ear effusion.

Tympanograms have been classified into

patterns related to various conditions of the

middle ear system. Jerger’s classification of

tympanograms

is

summarized in Figure 2. The

type A pattern is found in patients with intact,

mobile eardrums and good Eustachian tube

func-tion indicated

by

near-atmospheric middle ear

pressure. The type A curve represents slightly

stiffened tympanic membrane compliance, while

the A1) pattern represents the abnormally flaccid

tympanic

membrane.

Type

A tympanograms are

found generally in normal hearing or

sensori-neural hearing loss; type A patterns are generally associated with stapes fixation, tympanoscierosis,

the fixed malleus, or a heavily thickened or

scarred tympanic membrane. The AD pattern is

.

3 200 100 ( s100 .200

----AIR

PRESSURE----.-FIG. 2. Type A tympanograms characterized by maximum compliance at normal atmospheric pressure (0 mm H20 air pressure). Type B tympanograms show little or no change in compliance of tympanic membrane as air pressure in external ear canal is varied. Type C tympanograms show near-normal compliance with significant negative middle ear pressures (typically more severe than -150 mm H20). See text for additional explanation of tympanogram

classifica-tion.

most often associated with flaccid eardrums or

discontinuity of the middle ear ossicular chain.

The type B tympanogram represents a

nonmo-bile tympanic membrane. This condition may be

noted in ears with otitis media, perforations,

patent tympanic membrane ventilation tubes, excessive cerumen, or some congenital fixations.

The type C tympanogram represents an intact,

mobile tympanic membrane with poor

Eusta-chian tube function demonstrated by excessive

negative middle ear pressure. This curve may or

may not be related to the presence of middle ear

effusion.

An alternative tympanogram classification

sys-tem has been proposed by Paradise et al.8 These

(3)

i+m Piiysicu. VOLUME TEST

FIG. 3. Ear canal physical volume test (PVT) is used to evaluate intacthess of tympanic membrane. PVT

measure-ment in patient with tympanic membrane perforation or patent ventilation tube (bottom) is four or five times greater

than when tymparnc membrane is intact (top).

classification system comprised of five major

categories with seven distinct tympanogram

curves.

In their analysis of 280 pediatric subjects 7

months of age or older, tympanograms with

normal compliance and normal middle ear

pres-sure were rarely associated with effusion. The

presence of effusion in negative pressure

tympa-nograms (Jerger’s type C) was related to

the

degree of abnormal middle ear pressure and the

magnitude of the compliance function.

Low-peaked

negative pressure tympanograms were

much more likely to yield effusion than

high-peak ed negative pressure tympanograms.

EXTERNAL EAR CANAL PHYSICAL

VOLUME TEST

An interesting pediatric application of

im-pedan ce audiometry is the external ear canal

physical volume test (PVT) which is used to

evaluate intactness of the tympanic membrane

(Fig. 3). Impedance meters that record

com-pliance in terms of cubic centimeters can be used

to

perform

this test. if the tyniparnc membrane is

not intact the physical volume measure will be

quite large, often exceeding 4.0 or 5.0 cu cm.

Tympano-gram

Physical Volume (cu cm)

Probable Etiology

Type A 0.8-1.2 Normal middle ear

Type B < 0.3

0.8-1.2

> 2.5

Cerumen or canal wall

Serous otitis

Tympanic membrane

perforation or pressure equalization tube

Type C 0.8-1.2 Negative middle ear

pressure; inadequate Eustachian tube func-tion

Thus,

the physical volume measurement

can

be

used as a means to nile out a nonobservable

perforation

behind

an exaggerated

larger

than approximately 2.0 cu cm in children

must

be

due to the presence of a perforation or

patent ventilation tubes; flat tympanograms with

normal physical volumes are probably related to

serous

otitis

media;

abnormally

small physical

volumes may be related to cerumen occluding the

external

canal or perhaps the probe tip pressed against the canal wall (Table).

ACOUSTIC REFLEX THRESHOLD

The diagnostic implications of the acoustic

reflex outweigh considerably the contributions of

tympanometry

and static compliance

measure-ments.

The stapedial muscle contracts reflexively

when the ear is stimulated

with

a

sufficiently loud

sound. This contraction occurs bilaterally, even

when only one ear is stimulated. Researchers have

consistently

documented

that the necessary loud-ness

range

is 70 to 100 dB

hearing

threshold level

(HTL) (median value, 82.2 dB HTL) for pure-tone

signals and approximately 65 dB HTL for white

noise.9”#{176}

The lowest signal intensity capable of

eliciting

the acoustic reflex is recorded as the

acoustic reflex threshold for the stimulated ear.

Under some circumstances the clinician is

inter-ested

in

the presence or absence of the acoustic

reflex in the probe ear; on other occasions the ear

of interest is the earphone or stimulated ear.’1

In children

with

conductive hearing problems

the acoustic reflex can only be observed in mild

(4)

unilateral conductive hearing loss exceeds 30 dB

HTL the acoustic reflex is typically obscured

bilaterally. Thus, when the stimulating sound is

presented to the conductive hearing loss ear, the

30 dB + hearing loss is sufficient to prevent the

signal from being perceived loudly enough to

elicit the acoustic reflex. Then, when the

earphone is on the normal ear and the probe is in

the unilateral conductive loss ear, the mechanism

causing the conductive loss prevents the eardrum

from showing a change in compliance. Naturally,

in a bilateral conductive loss, the acoustic reflexes

will be absent bilaterally because the disease in

each prohibits the probe from noting a

compliance change when the opposite ear is

stimulated with sound. This acoustic reflex result

proves to be a tremendous asset in the evaluation

of unilateral conductive hearing loss in children

less than 3 years of age.12

Since conductive-type disease precludes

tym-panic membrane compliance change, the acoustic

reflex can be expected to be absent when the

probe tip is in a conductive loss ear regardless of how small an air-bone gap exists. The presence of

a small air-bone gap of only 10 dB is sufficient to

obscure the reflex in the probe ear nearly 80% of

the time.’3 Conversely, if acoustic reflexes can be

noted in the probe ear, it is virtually impossible for a conductive hearing loss to exist in that ear.

Thus, a very mild bilateral conductive hearing

loss will obscure the acoustic reflex bilaterally.

ACOUSTIC IMPEDANCE AND

OTITIS MEDIA

Otitis media is the most common cause of

hearing disorders in children. Estimates have

been made that between 76% and 95% of all

children have at least one episode of otitis media

by the age of 6 years.’4 Although one third of

children with isolated episodes of middle ear

effusion recover spontaneously, approximately

20% of children seen by primary care physicians

have recurrent otitis media.’5 The term

“otitis-prone” has been suggested to describe children having six or more episodes of otitis media before

starting 1

Unfortunately this common otologic disorder

too often goes undetected in children. There is no

doubt that neglected middle ear disease may lead

to more serious problems. Recurrent middle ear

effusions can result in a number of complications

which may ultimately require surgical treatment

to ventilate the middle ear, to close a perforation,

or remove cholesteatoma. Chronic otitis media

typically causes conductive impairment, but can

also lead to sensorineural hearing 1055.0718

It is becoming increasingly apparent that

recurrent

otitis

media with mild hearing loss may

contribute to educational problems.’9 Some of

these children may be labeled as “learning

dis-abled” or show behavior problems as a result of

their hearing problem. Ling’#{176} studied this

problem by comparing achievement test results

on two matched groups of schoolchildren; one

group had a history of hearing loss due to otitis

media and a second group of children reported

normal otologic history. The otitis media group

showed

severe delay in reading and arithmetic

skills when compared to the normal

control-group students. The degree of academic delay

correlated positively

with

the severity of hearing

loss, but even the children with the mildest losses

showed academic

handwap.

These findings have

since been confirmed by numerous other

investi-gators who agree that the academic impairment

due to conductive hearing loss is irreversible.”’3

The best way to avoid these educational problems

is to utilize better technique to identify children

with middle ear effusions as early as possible so

that treatment can be initiated.

Tympanometry is of notable value to

pediatri-cians as an objective method to follow the

progression of middle ear disease. Flow sheet

forms of blank tympanograms may be placed in

the child’s chart and tympanometric

measure-ments recorded successively each time the

patient is seen (Fig. 4). Prior to the presence of otologic disease and assuming the ear to be

otherwise healthy, a normal tympanogram is

displayed. Onset of the disease is coincident with

the obstruction of the Eustachian tube, thereby

creating a negative pressure value in the middle

ear.

This

early stage of disease yields a retracted

tympanic membrane tympanogram. Progression

of the disease results in effusion in the middle ear

cavity. Compliance of the tympanic membrane is

reduced

in this condition and a “nonmobile”

tympanogram is typically demonstrated. As the

disease responds to treatment and the effusion

begins to resolve, the negative pressure tympanic

membrane pattern reappears. Observation of this

progression can prove useful in evaluating the

natural history of middle ear effusions as well as

effectiveness of medical treatment. With the

return of the middle ear to a healthy status, a

normal tympanogram will once again be

exhib-ited. The ear with effusion may go through the

entire

disease

process with less than a 1O-dB change in hearing levels.

TYMPANOMETRY AND SCREENING

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FIG. 4. Tympanometry may be used as objective technique to follow natural history of middle

ear effusion or efficacy of medical treatment. Tympanograms are shown above on sample flow sheet as solid line against normal tympanogram curve in cross-hatched markings.

CLINICAL EXAM SRT TYMPANOGRAM

p#’O . _ d..;c1g - :7- ,

L.1-identification of ear disease are two separate

objectives, and the use of tympanometry does not

preclude the necessity of a hearing test. In a

thought-provoking essay on audiometry

screen-ing, Lescouflair lists four purposes for

audio-metric screening: (1) to identify even minimal

hearing loss; (2) to identify the presence of active ear disease; (3) to refer abnormal cases for medical

evaluation; and (4) to refer appropriate cases for

rehabilitation as necessary.’4 Tympanometry is

quite

sensitive

for

accurate identification of

medical ear problems, but a threshold hearing test

is absolutely necessary to identify possible hearing loss.

.T

-.2000

A

number

of investigators have conducted

screening studies to evaluate the efficacy and

accuracy of tympanometry, otoscopy, and

pure-tone screening. Brooks of Great Britain evaluated

543 schoolchildren with audiometry

and

tympa-nometry

and found only 81% agreement between

pure-tone

and

impedance screening. According to

Brooks, the major cause of disagreement was the

presence

of fluid in the middle ear which

did

not

create sufficient hearing loss for the child to fail

the hearing test.’5 McCandlless and Thomas

eval-uated

730 school-age children by means of an

audiometnic

screening at 20 dB HTL, otoscopic

(6)

revealed a 93% agreement between

tympanom-etry and otoscopy, with only a 61% agreement

between pure-tone screening and otoscopy.’6

In Scandinavia, Renvall et al.’7 compared

screening audiometry with results of otoscopy

and tympanometry in

200

ears of 7-year-old

children who had failed pure-tone hearing

screening

tests at school. Otoscopy identified

abnormalities in 85% of the total failure group,

while tympanometry identified abnormalities in

97% of the failure sample. In a second pant of the

same

study, the investigators evaluated

206

ears

from a group of randomly selected 10-year-old

children. In this sample, 1.5% failed pure-tone

screening,

8%

failed otoscopic examination, and

24% failed tympanometry screening.

Numerous studies exist indicating that

audio-metric hearing levels per se do not necessarily

identify

otologic abnormalities. Eagles et al.28

compared audiometric screening and otoscopic

examination

and reported that less than 50% of

the cases of middle ear disease were identified by

audiometry, with the average hearing loss of 14

dB associated with otitis media. Similarly, Cohen

and Sade’9 found that 50% of 408 ears with serous

otitis media would have passed as “normal” on

school

hearing

tests conducted at the accepted

screening level of 25 dB HTL. Clearly, pure-tone

audiometric screening is not the technique of

choice for the identification of ear disease, yet the

vast majority of school systems in the United

States continue to use screening audiometry

under

the misguided

impression that appropriate children will be selected for medical referral.

Some investigators have expressed concern that

the extreme sensitivity of tympanometry may

create problems of over-referral in auditory

screening programs.30’31 A report was recently

published suggesting “open-ended

tympano-metric

screening”

because middle ear effusions in

children may vary from day to day as indicated by

tympanograms changing from types A to C

during

onset

of the disease

and

from

types

B to

C

during remission stages. The open-ended

screen-ing concept advocates serial tympanograms on

successive days before a decision for referral is

reached.2

There is no question that, under proper

circum-stances and when time permits, the most

thor-ough evaluation of auditory problems is

accomplished through the use of otoscopic

exam-ination,

auditory

threshold

testing, and

tympa-nometry. When less than optimal conditions exist,

or when a well-qualified otoscopic examiner is

unavailable, tympanometry is undoubtedly the

most sensitive indicator of middle ear disease.

DISCUSSION

Impedance audiometry (tympanometry

and

acoustic reflex measurement) is an objective

measurement

of tympanic membrane mobility.

The PVT is a quick, effective means to evaluate

intactness of the tympanic membrane. These

techniques

are

of notable value to pediatricians in

the assessment and identification of otologic

disease in children. Tympanometry and the

measurement

of middle ear pressure are

particu-larly useful in monitoring the natural history of

middle

ear

effusions.

Impedance audiometry is

advocated as a supplementto otoscopic

examina-tion and audiometnic hearing tests. Equipment

manufacturers

are committed to the development

of small, easy-to-operate tympanometnic devices

for use in pediatric offices and school screening

programs. There have been numerous studies

repOrting normative data on the uses of

tympa-nometry

and middle ear pressure measurements,

and

confirming

their

value as a clinical tool with

children.

Mortimer33 analyzed the contributions of

impedance

audiometry

in a thoughtful and

complete manner. He acknowledged the four

main areas of value for tympanometry use as (1)

an adjunct for accurate diagnosis, (2) a screening

device,

(3) a

teaching tool, and (4) a means for following the natural course of middle ear disease.

Mortimer pointed out that the use of

tympanom-etry as a supplement to otoscopy would yield

greater diagnostic accuracy; that it provides a

mechanism by which diagnostic impressions can

be confirmed; and that the use of tympanometry

might lead to better understanding about the

natural

history of serous otitis media.

Early detection of middle ear effusions seems a

highly

desirable goal from both the medical and

educational point of view. Unfortunately, too

often this insidious disease process exists when the

patient, parents, teacher, and even, perhaps, the

physician may all be unaware of the problem. The

present methods of otoscopy

and

audiometry

have some limitations, leading European

physi-cians to advocate the use of tympanometry as the

best means to identify middle ear effusions in

mass screening programs. Acoustic impedance

measurements are not tests of hearing, nor can

they replace otoscopic examination. HOwever, it

seems likely that the pediatric evaluation of

middle

ear

effisions will be greatly enhanced

through the use of tympanometry, the ear canal

PVT, and acoustic reflex threshold determination

as supplements to traditional diagnostic

(7)

REFERENCES

1. Bluestone CD, Shurin PA: Middle ear disease in

chil-dren: Pathogenesis, diagnosis and management.

Pediatr Clin North Am 21:379, 1974.

2. Ehrlich MA, Tait CA: The application of acoustic impedance measurements to pediatric clinical

prac-tice.Pediatrics 55:666, 1975.

3. McCurdy JA, Goldstein JL, Gorski D: Auditory screening of preschool children with impedance audiometry: A comparison with pure tone audiom-etry: Detecting otologic disease prior to the onset of hearing loss. Clin Pediatr 15:436, 1976.

4. Stool SE, Anticaglia J: Electric otoscopy-a basic

pedi-atnc skill. Clin Pediatr 12:420, 1973.

5. Howie VM, Ploussard JH: Treatment of serous otitis media with ventilatory tubes. Clin Pediatr 13:919, 1974.

6. Paradise JL: Pediatrician’s view of middle ear effusions: More questions than answers. Ann Owl Rhino! Laryngol 85(suppl 25):20, 1976.

7. Jerger JF: Clinical experience with impedance audiom-etry. Arch Otolaryngol 92:311, 1970.

8. Paradise JL, Smith CG, Bluestone CD: Tympanometric detection of middle ear effusion in infants and young children. Pediatrics 58: 198, 1976.

9. Metz 0: Threshold of reflex contractions of the muscles

of the middle ear and recruitment of loudness. Arch Otolaryngol 55:536, 1952.

10. Jepsen 0: Middle ear muscle reflexes in man, in Jerger J (ed): Modern Developments in Audiology. New

York, Academic Press, 1963, pp 193-239.

11. Northern JL, Downs MP: Hearing in Children.

Balti-more, Williams & Wilkins Co, 1974, pp 174-189.

12. Northern JL: Clinical applications of impedance audiometry, in Northern JL (ed): Hearing Disorders.

Boston, Little Brown & Co, 1976, pp 20-36.

13. Jerger J, Anthony L, Jerger 5, Mauldin L: Studies in impedance audiometry: III. Middle ear disorders.

Arch Otolaryngol 99:165, 1974.

14. Howie VM, Ploussard JH, Sloyer JL: Natural history of

otitis media. Ann Owl Rhino! Laryngol 85(suppl 25):18, 1976.

15. Brooks DN: School screening for middle ear effusions.

Ann Otol Rhino! Laryngol 85(suppl 25):223, 1976. 16. Howie VM, Ploussard JH, Sloyer J: The “otitis-prone”

condition. Am I Die Child 129:676, 1975.

17. Paparella MM, Brady DR: Sensorineural hearing loss in

chronic otitis media and mastoiditis. Arch

Otolar-yngol 74:108, 1970.

18. English GM, Northern JL, Fria TJ: Chronic otitis media as a cause of sensorineural hearing loss. Arch

Otolaryngol 98:18, 1973.

19. Avery AD, Lelah T, Solomon NE, et al: Quality of medical care assessment using outcome measures: Eight disease-specific applications. Rand Report,

R-2012/2-HEW, August 1976, pp 608-610. 20. Ling D: Rehabilitation of.cases with deafness secondary

to otitis media, in Glorig A, Gerwin KS (eds): Otitis media: Proceedings of the National Conference,

Collier Hearing and Speech Center, Dallas, Texas. Springfield, Ill, Charles C Thomas Publisher, 1972,

pp 249-253.

21. HoIm VA, Kunze LH: Effect of chronic otitis media on language and speech development. Pediatrics

43:833, 1969.

22. Lewis N: Otitis media and linguistic incompetence. Arch Otolaryngol 102:387, 1976.

23. Downs MP Hearing loss: Definition, epidemiology and

prevention. Public Health Rev 4:255, 1975. 24. Lescouflair G: Critical view on audiometric screening in

school. Arch Otolaryngol 101:469, 1975.

25. Brooks DN: Hearing screening: A comparative study of

an impedance method and pure tone screening.

Scand Audiol 2:67, 1973.

26. McCandless G, Thomas GK: Impedance audiometry as a

screening procedure for middle ear disease. Trans Am Acad Ophthalmol Otolaryngol 78:2, 1974. 27. Renvall U, Liden G, Jungert S. Nilsson E: Impedance

audiometry as screening method in school children.

Scand Audiol 2:137, 1973.

28. Eagles EL, Wishik SM, Doerfier LG: Hearing sensitivity

and ear disease in children: A prospective study.

Lanjngoscope, suppl 1967, pp 1-274.

29. Cohen D, Sade J:Hearing on secretory otitis media. Can

I Owl 1:27, 1972.

30. Orchik DJ, Herdman 5: Impedance audiometry as a

screening device with school age children. I Md

Res 14:283, 1974.

31. Cooper JC, Gates GA, Owens JH, Dickson HD: An

abbreviated impedance bridge for school screening. I Speech Hear Disord 40:260, 1975.

32. Lewis N, Dugdale A, Canty A, Jerger J: Open-ended

tympanometry screening: A new concept. Arch Otolaryngol 101:722, 1975.

33. Mortimer EA Jr: Impedance audiometry: Is It a wise

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1978;61;761

Pediatrics

Jerry L. Northern