Download Clinical and Communication Access through Amplification for a

J Am Acad Audiol 4 : 426--431 (1993)
Clinical and Communication Access through
Amplification for a Medical Student with
Severe Hearing Loss : Case Report
David A. Fabry*
Abstract
This case report focuses on the communication difficulties of a 21-year-old medical student
with severe-to-profound sensorineural hearing loss . The greatest difficulties reported by the
patient were for stethoscope use and slide presentations in darkened rooms. Successful
audiologic management was accomplished for this patient via use of a behind-the-ear (BTE)
FM system for classroom use and a "homemade" amplified stethoscope that enabled him to
hear diagnostic heart sounds for clinical use. The amplified stethoscope provided greater lowfrequency gain for this patient than was available through other commercial units.
Key Words:
FM system, hearing aid, hearing loss, stethoscope
his case presented several interesting
challenges for the evaluation and fitT ting of a hearing aid on an individual
with severe-to-profound hearing loss . At the
outset, less research has focused on the "optimal" insertion gain requirements for this magnitude of hearing impairment than for people
with mild and moderate hearing losses (Libby,
1986 ; Schwartz et a1,1988 ; Byrne et a1,1991) . In
addition, because this patient was a first-year
medical student, he required amplification under some relatively demanding listening situations, and he also had been unable to use a
stethoscope effectively . The problem of effective
use of a stethoscope had also been a frequent
concern of other hearing-impaired medical personnel seen in our clinic . The following case
represents efforts over several months to provide this individual with the amplification necessary to allow him to achieve his professional
goals without undue burden .
*Section of Audiology, Mayo Clinic, Rochester, Minnesota
Reprint requests : David A . Fabry, Section of Audiology, Mayo Clinic, 200 First Street SW, Rochester,
MN 55905
426
CASE REPORT
Subject
The patient, a 21-year-old male, reported to
the Otorhinolaryngology Department at the
Mayo Clinic in the fall of 1991 for a routine
examination prior to beginning studies at the
Mayo School of Medicine . He had previously
been diagnosed with hearing loss at 3 years of
age, as a result of mumps and chickenpox. No
family history of hearing impairment was reported, and the patient denied tinnitus or vertigo . He had worn amplification subsequent to
the diagnosis of hearing loss ; presently, he was
wearing a Viennatone AO PPII behind-the-ear
(BTE) hearing aid in his left ear. He had previously tried (and rejected) binaural and BICROS
amplification.
The patient reported that he communicated
well under most listening situations when auditory and visual cues were available, but the two
most difficult situations for him were : (1) stethoscope use, which was impossible with his hearing aid; and (2) classroom instruction with the
lights dimmed, during slide or film presentations.
Audiometric Findings
Audiometric evaluation revealed asymmetric bilateral sensorineural hearing loss, with
Amplification for a Medical Student/Fabry
Frequency (Hz)
0
250
500
10
30
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m
z
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x
as
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-T .
:.
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0
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" *ibrotactile
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ro
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: . . . . . . .. .. . .. . .. . . . :. . .
. . . . . . . . . . . . .'* . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
30
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.
.j(\,X
. . . . . . . . . . . . . . . . . : . . . . . . . . . . . . . . . . . .X . .
. : . . . . . . . . . : .%~. . . . . . : . . . . . . . . . : . . . . . . . . . : . . . .X
90 _ . . . : . . . . . . . . . : . .
. . . . . . . . . . . . . .X
:...
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/ . . . . . : . . ._ 90
100
100
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110
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X
left AC
O right AC
>
BC
Figure 1 Audiologic data, revealing bilateral asymmetric sensorineural hearing loss .
profound hearing loss in the right ear and 0
percent speech recognition for stimuli presented
at any sensation level. Thresholds from the left
ear indicated severe-to-profound hearing loss,
with a speech-recognition threshold (SRT) of 78
dB HL and a speech-recognition score of 60
percent for recorded monosyllabic words (CID
W-22) presented at 20 dB SL (Fig . 1) . Acoustic
reflexes were consistent with cochlear pathology, as suggested by levels within 90th percentile levels as a function of hearing loss (Silman
and Gelfand, 1981). The only bone-conduction
thresholds measured (due to equipment limitations) were at 250 and 500 Hz and were reported
by the patient to be tactile responses .
Real-ear measurements of the patient's
Viennatone AO PPII BTE hearing aid at "use
m
50
e
4
q
0
30
m
100
1000
10000
Frequency (Hz)
Figure 2 Real-ear insertion gain measurement for
Viennatone BTEhearing aid using 65 dB SPL composite
noise. POGO prescriptive target is shown by the dashed
line .
130
a
m
b 120
110
- Viennatone AO PPII
100
100
Figure 3
90 dB SPL RESR
1000
Frequency (Hz)
10000
Real-ear saturation response for Viennatone
BTE hearing aid using 90 dB SPL composite noise .
gain" revealed approximately 50 dB of insertion
gain for the frequency region from 250 to 1200
Hz, with gain decreasing above 1200 Hz at a
rate of 15 dB per octave (Fig. 2) . These measurements were made with the composite noise
signal of a FoniXTM 6500 Quick Probe TM test
system presented at 65 dB SPL. Insertion gain
results matched "Prescription of Gain/Output
(POGO) of Hearing Aids" prescriptive thresholds (McCandless and Lyregaard, 1983) more
closely than either Berger (Berger et al, 1989) or
National Acoustics Laboratories' (NAL) target
values (Byrne and Dillon, 1986), but all prescriptive formulae underestimated the actual
low-frequency gain preferred by the patient.
Recently, Byrne et al (1991) recommended that
the NAL prescriptive formula, which is essentially a modification of the half-gain rule, be
revised to recommend two-thirds gain for persons with hearing loss greater than 60 dB HL .
Even if this rule had been applied, the use-gain
setting preferred by the patient exceeded that of
all prescriptive targets, and efforts to decrease
low-frequency gain decreased user satisfaction
considerably . The reduced high-frequency gain
relative to prescriptive targets is understandable, because this prevented feedback from occurring at use gain, and also it is unlikely that
speech audibility could be achieved without
discomfort for frequencies above 1500 Hz .
Aided real-ear saturation response (RESR)
measurements made with 90 dB SPL composite
noise revealed that the hearing aid's peak sound
pressure level approached 140 dB at 900 Hz
(Fig. 3) . No discomfort was reported by the
patient for composite noise, narrow-band noise
centered at 1000 Hz, or recorded environmental
sounds (Volume 2, Tracks 21, 22, 35, and 51)
from a commercially available compact disk
(Jelonek, 1990), all presented in the sound field
Journal of the American Academy of Audiology/Volume 4, Number 6, November 1993
at 90 dB SPL from a loudspeaker positioned 1
meter distant from the subject at 45 degrees
azimuth. Two-cc coupler measurements ofhearing aid input/output function at use gain indicated that the hearing aid provided linear amplification for composite noise inputs below 80
dB SPL.
BTE FM System
fin
50
y 40
30
- ~xlchd
Ear, hearing aid only
20
100
1000
10000
Frequency (He)
Figure 4 Real-ear insertion gain measurement (65 dB
SPL composite noise) for the Extend-EarTm FM BTE in
the hearing-aid-only mode (solid line) andthe Viennatone
BTE (dashed line).
428
50
y 40
a0
30
20
The patient reported that his most difficult
communication situation was in classroom settings, where the lights would frequently be
dimmed for slide presentations. Typically, discussion would be limited to a single lecturer, but
the reverberant conditions in the room and the
lack of visual cues placed him at a considerable
disadvantage for communication.
The patient had tried FM classroom amplification in the past, but was reluctant to use
these devices because (1) they were never
matched well to the frequency response of his
personal hearing aid; and (2) he did not prefer to
wear body-aid amplification systems for cosmetic and performance reasons.
At the time of this patient's initial visit, the
prototype of a BTE FM hearing-aid system
(Extend-EarTM) had been introduced by AVR
Communications . Purchase of this device for
the patient was arranged through the Mayo
Medical School . The Extend-EarTM uses an integrated FM-receiver hearing aid that is similar
in size to other high-power BTE hearing aids .
The transmitter is a body-aid-sized device with
an omnidirectional lapel electret microphone
that also serves as the antenna. The hearing aid
may be used for FM-only, hearing-aid-only, or
combined FM/hearing-aid applications .
Two potentiometers were adjusted to fine-
11
e
80
100
1000
10000
Frequency (He)
Figure 5 Real-ear insertion gain measurements (65 dB
SPL composite noise) for the Extend-EarTM FM BTE in
FM-only mode for maximum (dotted line) and minimum
(solid line) low-frequency tone-control adjustments on
the FM transmitter .
tune the BTE receiver's frequency response and
output to match the hearing-aid-only insertion
response of the Extend-EarTM to that of the
Viennatone for 65 dB SPL composite noise (Fig .
4) .
Another useful feature of the Extend-EarTM
device is that the transmitter contains both
volume and tone controls, to allow adjustment
of the FM signal relative to the hearing-aid
signal for combined modes. Figure 5 shows the
effects of varying only the user-controlled tone
wheel from maximum (dotted line) to minimum
(solid line) values .
After final adjustments were made to provide a close match to real-ear insertion response
(REIR) and RESR measures made with the
patient's personal hearing aid, he was instructed
to wear the Extend-EarTM device for classroom
and leisure use for a period of 1 week .
Observations
The patient returned after a 1-week trial
with the BTE FM system and reported that it
was very helpful for numerous listening environments . He reported the sound quality to be
very similar to his personal hearing aid, and the
signal-to-noise ratio, when worn on FM-only
setting, was improved substantially over his
conventional hearing aid for lecture situations .
Overall, he was extremely satisfied with the
performance and cosmetic benefits over other
FM systems that he had tried previously, although the rather "square" design of the BTE
case caused some mild discomfort to his pinna
after several hours of continuous use.
Some of the comments made by the patient
Amplification for a Medical Student/Fabry
were similar to those made by users of other FM
systems, including the inability to hear environmental sounds when worn in the FM-only mode .
In addition, because this unit is a wide-band
system, the operating range was limited when
compared to narrow-band systems. The patient
reported a maximum transmission range of
approximately 50 feet, after which intense static
interference quickly eliminated the benefits of
FM transmission . Another problem was that
static interference resulted when the microphone/antenna cable became looped; this problem was solved by insulating the cable with a
piece of rubber tubing over its 2-foot length .
Perhaps the greatest difficulty that the patient experienced with the Extend-EarTM is the
lack of a telecoil switch . Because of the magnitude of his hearing loss, he relies heavily on the
telecoil of his Viennatone BTE for telephone
conversation. Although the FM transmitter can
be used to pick up the signal from the telephone
receiver, the procedure necessary to accomplish
this is quite awkward and not very practical. It
would be helpful if future versions of this device
incorporated a telecoil .
Amplified Stethoscope
Overall, the FM BTE provided a solution to
this patient's difficulty in communicating in
classroom settings, but not for using a stethoscope. The patient had previously tried amplified stethoscopes without success, due to problems related to distortion and feedback . One
option was to interface the output of a commercially available amplifying stethoscope (Starkey
ST3) to the auxiliary input of the FM transmitter, but the sound quality was still determined
to be inadequate for monitoring the necessary
cardiovascular landmarks.
The typical frequency response for a
Littmann cardiology stethoscope, which is in
widespread use by medical personnel, shows a
pronounced low-frequency peak at approximately 75 to 125 Hz when measured in the 2-cc
coupler (Fig . 6) . Furthermore, Figure 6 indicates that the information necessary for auscultation diagnosis is primarily low frequency in
nature ; this does not include high-frequency
information required for diagnosing some lung
sounds . Figure 7 shows the frequency response
ofthe Starkey ST3 amplified stethoscope, which
uses the Littmann Classic diaphragm, as measured on the 2-cc coupler for 65 dB SPL of
composite noise. The measurements suggest
that maximum coupler gain was approximately
55 dB (at 800 Hz), but only about 25 dB of gain
was provided for frequencies below 250 Hz . The
m
m
- Littmann Cardiology Stethoscope
-
b 40
a
a
a
m
m
10
100
Frequency (He)
1000
10000
Figure 6 Coupler measurement ofa standard Littmann
cardiology stethoscope .
ST3 offers no trimpots for adjustment of the
stethoscope's frequency response or maximum
output .
Because of a lack of commercially available
options for amplified stethoscope use, a
"homemade" stethoscope was built that would
better compensate for the patient's degree and
configuration of hearing loss . A standard
Littmann Classic stethoscope was modified,
using an in-the-ear faceplate (Siemens LSI PP2)
containing twin BK receivers (3021) mounted
on the housing of an amplified stethoscope
(Starkey ST3) . This arrangement provided
greater low-frequency gain than the commercial unit and incorporated an adjustable tone
control, providing 46 dB of gain at 500 Hz .
Furthermore, the circuit was mounted closer to
the diaphragm head (Fig. 8) than for the Starkey
ST3 amplified scope (Fig . 9), in an effort to
minimize acoustic feedback . Figures 10A and
10B show the frequency response and input/
output function, respectively, for the "homemade" manufactured device measured in the 2cc coupler.
m
m
0
e
30
- Starkey
20
100
ST3 amplified
stethoscope
1000
Frequency (Hs)
10000
Figure 7 Two-cc coupler measurement of a Starkey
ST3 amplified stethoscope for 65 dB SPL composite
noise.
Journal of the American Academy of Audiology/Volume 4, Number 6, November 1993
Figure 9
Figure S
"Homemade" amplified stethoscope.
Observations
The patient has been using the "homemade"
amplified stethoscope successfully for several
months . His medical school professors have
listened to the stethoscope and report that it
provides a reasonably faithful reproduction of
sounds necessary for auscultation diagnosis.
The patient's primary complaints are related to
convenience ; for example, because an in-the-ear
faceplate was used, size 13 batteries were used,
which are incompatible with the 675 cell used by
both the Viennatone and Extend-EarTM hearing
aids . The patient, however, has adapted to carrying an extra set of 13 and 675 batteries, in the
event that either amplifying device fails.
Starkey ST3 amplified stethoscope .
sons with severe-to-profound hearing loss, however, one solution may be to custom design a
stethoscope to provide selective amplification
and output that is appropriate for their hearing
loss without producing acoustic feedback .
The subject ofthis case report has benefitted
from both the FM hearing-aid system and the
"homemade" amplified stethoscope. It is unclear whether these devices will enable him to
specialize in a medical area requiring acoustic
monitoring of subtle chest or heart sounds, but
they provide a reasonable solution at the present
time for someone with his degree of hearing
loss . Perhaps emerging technology will provide
more sophisticated signal processing and audiovisual data analysis .
Acknowledgment . The author thanks Scott Fruth
and Greg Hovland for their capable technical support in
modifying the amplified stethoscope to our requirements .
The support of the Sheldon F. Reese Foundation is also
appreciated.
CONCLUSIONS
F
or persons with mild or moderate hearing
loss, conventional amplified stethoscopes
or deep-fitting hearing aids may provide a viable solution to auscultation diagnosis. For per-
130
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- Input/output, Homemade amplified
stethoscope
b
a
110
0
100
B
Frequeacy (He)
Figure 10
90 L_
50
I
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70
,
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90
Input (dB)
Composite noise 2-cc coupler measurements of the homemade amplified stethoscope for gain with
65 dB SPL
composite noise (A) and input/output function (B).
430
Amplification for a Medical Student/Fabry
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Byrne D, Dillon H. (1986) . The National Acoustic Laboratories' (NAL) new procedure for selecting the gain and
frequency response of a hearing aid. Ear Hear 7(4) : 257265.
Schwartz D, Lyregaard PE, Lundth P. (1988) . Hearing
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41(2):13-17 .
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Jelonek S. (1990) . The Most Current and Authentic Liuing Sound Effects. Vols . 111. Palo Alto, CA: Micro Sound
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