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OCR for page 55
4
Treatments
Over the years the treatments attempted for tinnitus have
covered the range from vitamins and drugs to hypnosis and
masking, but far and away the most common treatment--and
in terms of absolute numbers helped, probably the most
effective one--has been simple reassurance from a hearing
professional that mild tinnitus is not a rare disorder,
not necessarily a harbinger of imminent deafness, not a
symptom of serious brain disorder, etc. One specialist
estimates that explaining the problem is a sufficient
solution for 95 percent of the tinnitus sufferers he sees
(CIBA Foundation, 1981:273), and this statistic presum-
ably ignores those patients satisfied by the explanations
of general practitioners or others prior to referral to
specialists.
When they are being precise, medical specialists often
reserve the use of the word treatment for actions taken
to actually cure a disorder or disease, as opposed to
actions taken only to relieve the pain or distress of the
disorder or disease. The latter is technically termed
palliation or palliative treatment. As will be seen, in
these terms essentially every procedure described below
should be viewed as (at most) a palliative, even though
the word treatment may be used in discussing it.
PSYCHOLOGICAL INTERVENTION
As is true for many other serious ailments, tinnitus has
the potential to create or to intensify psychological
problems. Indeed, it might be argued that, in the past
at least, tinnitus was more likely than many other mala-
dies to have psychological concomitants because of the
unresponsive and apparently uncaring reaction of medical
55
OCR for page 56
56
professionals to the problem. A patient diagnosed as
having cancer, for example, may have a strong psychologi-
cal response to the news, but typically he soon begins to
receive medical treatments of various sorts for the prob-
lem. By contrast, all too often the tinnitus sufferer was
offered no treatment of substance and no hope of one in
the future. It is fully believable that after one or two
experiences of this sort, the frustrated tinnitus sufferer
would begin to evidence behaviors in accord with psycho-
1 Anal interpretations of the origin of the tinnitus.
m at is, it is imperative to realize that the plight of
tinnitus sufferers has, until very recently, been largely
ignored, and, as a consequence, the discovery of varia-
tions from "normal" in their psychological profiles cannot
be unequivocally identified as cause or effect of their
tinnitus problem.
Considerable evidence and simple logic indicate that
tinnitus is a symptom of various physiological anomalies
of the auditory and other systems and that these condi-
tions probably strike people of all personality types
indiscriminately. This is not to say that, once present,
a tinnitus will not be better handled by one person than
another, nor that transient psychological difficulties
cannot cause people to focus on or exaggerate a preexist-
ing or new physiological malady; the point is that psy-
chological makeup is probably a minor contributing factor
to the underlying anomaly. Ambrosino (1981) agrees that
there is no one personality type more likely to contract
severe tinnitus, but that once contracted, tinnitus can
affect personality. House (1981) studied the personali-
ties of 150 seriously afflicted tinnitus patients, and
Hazell (1981a) administered personality inventories to
his 200 patients, but no attempts were made to partition
cause from effect.
The possibility of interplay between psychological and
physiological factors is obvious when stress is consid-
ered. (Many tinnitus sufferers report exacerbation of
their problem during times of stress.) It is known that
psychological stress in a person's private or professional
life can produce concomitant physiological changes. If
some of these changes are responsible for a new or an en-
hanced tinnitus, it is understandable that a person might
come to focus on this obvious symptom as the source of all
his or her problems. Untangling this web might be compli-
cated indeed, and both too time-consuming for and beyond
the training of the typical hearing professional. m e
temptation is often great to refer such cases to psycho
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57
therapists; in the past this course has often been pursued
too hastily--and ineffectively--since many patients balk
at such treatment for what they strongly regard to be a
physiological problem. A treatment procedure aimed at
general relaxation--for example, biofeedback or just in-
structions to simply "slow downn--has appeal in such
cases. Anecdotes abound about tinnitus symptoms dimin-
ishing or disappearing upon the natural disappearance of
stress-inducing factors in a patient's life.
SURGERY FOR TINNITUS
Tinnitus is known to be a frequent, early symptom of
tumors of the internal auditory meatus and the cerebello-
pontine angle and of a glomus jugulare. It also can
herald the onset of otosclerosis or indicate the presence
of vascular anomalies of various sorts. Clearly, several
of these conditions require surgical attention, and in
the process, the tinnitus might be alleviated. But such
surgery should be distinguished from that performed solely
as a treatment for a severe tinnitus.
Over the years, various surgical techniques have been
attempted as a last resort to alleviate debilitating tin-
nitus. mese include tonsillectomy, sectioning of the
vestibulo-facial anastomoses (Fisch, 1970), excision of
the tympanic plexus (tympanosympathectomy; Lempert, 1946),
excision of the main trunk of the vestibular nerve (Fisch,
1970), sectioning of the cochlear nerve (Fisch, 1970),
and dorsal sympathectomy (Johnson, 1954), to name a few.
Results have been unpredictable at best, and success
rates have been low.
House and Brackmann (1981) reviewed reports of the
effects on tinnitus of various surgical procedures per-
formed for tinnitus relief, as well as for reasons other
than tinnitus relief. Following successful removal of an
acoustic neuroma, about 40 percent of the patients felt
that the tinnitus was better and about 50 percent felt it
was worse. Following successful stapedectomy, 74 percent
reported the tinnitus to be absent or reduced. Following
translabyrinthine section of the eighth nerve, about 45
percent of the patients felt that the tinnitus was absent
or improved.
As long ago as 1928, Jones and Knudsen were advising
against sectioning of the eighth nerve and destruction of
the cochlea as treatments for intractable tinnitus--not
because of a concern for the loss of useful hearing, but
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58
because of the general ineffectiveness of these proce-
dures. Sectioning of the eighth nerve and labyrinthectomy
are described as partly or wholly effective against tin-
nitus in about 50 percent of the cases (Hazel!, 1979c),
but it must be recalled that these percentages are pre-
sumably based upon small numbers of seriously debilitated
patients. Thus, failure must be particularly disappoint-
ing to the patients. We have no way of estimating how
many operations of these types are still performed, but
they continue to appear to be ill advised solely as treat-
ments for tinnitus. As Hazell (CIBA Foundation, 1981:213)
has pointed out, cutting the eighth nerve may obviate the
later use of other, possibly more effective treatments
yet to be developed. (Surgical procedures advocated for
Meniere's Disease and its attendant tinnitus were dis-
cussed in the section ~Meniere's Disease" in Chapter 2.)
EXPOSURE TO INTENSE SOUND
From personal experience, it appears that any brain-
storming session on tinnitus that includes people of vary-
ing levels of knowledge about the topic is likely to
eventually produce a question of the following sort:
Might it be possible to eliminate a narrowband tinnitus
by selectively destroying the spectral region giving rise
to it? The question often takes the more explicit form:
Might exposure to a narrowband or tonal stimulus of high
intensity be capable of "burning out" a tinnitus-
producing spectral region? (The idea also occurred to
Jones and Knudsen [1928].) It would be difficult indeed
to enumerate the implicit assumptions underlying such a
suggested treatment for tinnitus, and the likelihood is
that, once enumerated, the prospects for success would
remain sufficiently dubious that one would be reluctant
to attempt the procedure even on well-informed volunteers.
Fortunately, this difficult ethical predicament need not
be faced by anyone, for a bold experimenter has already
attempted the procedure on his own tinnitus.
I. M. Young had a unilateral, high-frequency tinnitus
that was highly annoying; over a period of time, he
administered various high-intensity sounds to himself and
then carefully documented the aftereffects of these expo-
sures (Young and Lowry, 1981, 1982). m e upshot is that,
even after heroic attempts, he has not been successful in
eliminating his tinnitus, although he has produced some
interesting effects that are difficult to explain. For
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59
example, following one series of monaural exposures, the
previously monaural tinnitus became permanently binaural.
Then, following a monaural exposure of 121 dB SPL at 500
Hz for 21 minutes, the tinnitus frequency was greatly
reduced in both ears and it remained so long after hear-
ing had returned to normal. Over the course of weeks, it
gradually returned to its original frequency, but with
different recovery rates in the two ears.
From this one well-studied subject, it appears that
tinnitus will not succumb to high-intensity sounds, but
logically some form(s) of tinnitus of different etiology
might be reduced by this procedure. Since exposure to
intense sounds is known to produce both temporary and
permanent tinnitus (as discussed in "Possible Experimental
Models of Tinnitus" in Chapter 2), future investigators
are encouraged to proceed cautiously even if using them-
selves as subjects.
DRUGS AND TINNITUS
Some drugs can cause or exacerbate tinnitus--and thus
their termination can alleviate tinnitus. Other drugs
can reduce or eliminate tinnitus--and thus are admin-
istered to alleviate tinnitus. Since termination and
administration of drugs can both be considered forms of
treatment, we discuss the two types of drugs here, in
successive sections.
Drugs Causing Tinnitus
It is not uncommon for patients with various maladies to
report tinnitus for the first time soon after beginning a
new drug regimen. For any particular drug, the fraction
of patients reporting new or enhanced tinnitus is typi-
cally small, but this should not lead us to disbelieve
the reality of the reports. Given the large number of
ways and locations in which tinnitus can arise, and given
the large individual differences in reaction to drugs at
the same dosage level, great heterogeneity of response
ought to be the rule. Some of the drugs noted for their
ability to induce or enhance tinnitus have been noted by
Brown et al.(1981) and Goodey (1981). On the other hand,
lists such as these and the one prepared by Drucker (1979)
must necessarily exaggerate the number of drugs that
actually produce tinnitus in a significant fraction of
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60
their users. It must be remembered that tinnitus is a
very common experience and thus might begin "spontane-
ously" while someone is taking a drug that should not
itself be held responsible for the tinnitus. Consider-
able work will have to be done before we truly know which
drugs possess the ability to induce tinnitus in normal
and abnormal auditory systems.
, _ .
Salicylates Aspirin, of course, is the most commonly used
drug known for its effects on hearing and tinnitus. After
iust 48 hours on a dosage of about 4.8 g/day, there is
10-15 dB of hearing loss (McCabe and Dey, 1965), and this
can grow with continued use to as much as 40-50 dB (Myers
and Bernstein, 1965).
Typically, the hearing loss is
essentially flat across frequency, but in some reports
the high frequencies are more affected than the low
(McCabe and Dey, 1965; McFadden and Plattsmier, 1982c).
Upon termination of the drug, the hearing loss invariably
recovers within 24-72 hours, depending upon the serum
salicylate level achieved (Myers and Bernstein, 1965;
McFadden and Plattsmier, 1982c).
At present there is contradictory evidence as to the
site of action of salicylate in the peripheral auditory
system. Gold and Wilpizeski (1966) observed diminutions
in the whole-nerve response with weak acoustic stimuli
but not with intense stimuli (unfortunately, they did not
simultaneously record the cochlear microphonics). Silver-
stein et al. (1967) reported a strong depression in both
the cochlear microphonic (CM) and the whole nerve action
potential (N1) following intraperitoneal injections of
sodium salicylate. A possible explanation of these two
resorts is that the salicYlate affects the hair cells and
that this ettect is then rerleccea In one response OL C11=
eight-nerve fiberse However, Wilpizeski and Tanaka (1967)
and Mitchell et al. (1973) found no change in CM response,
only a diminution in N1 following salicylate injections
Knowing whether or not the CM response is affected by
salicylates is basic to insights about site(s) and mode(s)
of action of this drug. Resolution of this discrepancy
and integration of the outcome with the established
effects of salicylates on the strict vascularis (see Wood-
ford et al., 1978, for a review) would be welcome and
valuable.
Tinnitus is commonly reported as a concomitant of
heavy aspirin usage. Indeed, its presence is routinely
used as a gauge of whether the salicylate level in the
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61
blood has reached the value believed to be necessary for
effective anti-inflammatory action. Emus, dosage is often
increased until tinnitus is produced and then decreased
until the tinnitus just disappears. (Morgan et al. [1973]
warn that this procedure is very unreliable as a predictor
of serum concentrations of salicylate, particularly in
patients with preexisting, high-frequency hearing loss;
many of these people never experience tinnitus, even at
very high serum concentration levels.)
Aspirin-induced tinnitus is typically characterized as
tonal and of high frequency, but no systematic investiga-
tions of its quality, pitch, and loudness as a function
of blood salicylate level have been done. McCabe and Dey
(1965) apparently did some informal pitch matching, which
indicated tinnitus frequencies from 7 to 9 kHz. It has
been reported that subjectively the tinnitus onset appears
to precede the hearing-loss onset (Morgan et al., 1973),
and there is an implication that it also recedes more
rapidly than the hearing loss upon termination of the drug
(in accord with the personal experience of the author,
but see CIBA Foundation, 1981:130-131), but these timing
relations are not well documented. Future experiments
aimed at this timing issue should incorporate measures of
relative hearing sensitivity at frequencies above the
normal audiometric range.
No mention could be found in the literature of two
features of aspirin-induced tinnitus that the author has
personally observed. Attempts to match the pitch of an
aspirin-induced tinnitus were frustrated by residual
inhibition; a brief, relatively weak matching tone pre-
sented to either ear had the ability to eliminate the
tinnitus for periods of 30-60 seconds as soon as its
frequency approximated that of the tinnitus. Second,
clenching of the jaw muscles would produce transient
increases in the magnitude of the tinnitus (also see CIBA
Foundation, 1981:202; Shulman, 1981a:184). Both of these
effects were observed in three listeners taking approxi-
mately 5 g of aspirin per day. Unfortunately, the two
effects do little to reduce the number of possible expla-
nations of the origin of the aspirin-induced tinnitus.
An intriguing but unlikely possibility is that this tin-
nitus might have as its basis a spontaneous otoacoustic
emission (OAK; see " m e Objective/Subjective Issue" in
Chapter 2).
Great individual differences in serum salicylate
levels and hearing loss have been reported for the same
weight-corrected dose levels (Myers and Bernstein, 1965;
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62
Mongan et al., 1973). Of both theoretical and practical
importance would be information on the relationship
between susceptibility to aspirin-induced hearing loss
and tinnitus and susceptibility to temporary and perma-
nent threshold shift. If eye color and melanin content
(see "Lidocaine" in this chapter) are highly predictive
of both, an important insight will be gained.
Finally, in regard to temporary threshold shift,
Hamernik and Henderson (1976) have reported negative
results from animal (chinchilla) experiments aimed at
detecting potent~atzon ot noise exposure by adminis-
tration of sodium salicylate, but McCabe and Dey (1965)
reported greater losses in absolute sensitivity following
noise exposure when their (human) listeners were on a
therapeutic dose of aspirin than when not (in accord with
~ ~ His issue should be
resolver, given the great quantities of aspirin consumed
daily by workers in noisy environments.
McFadden and Plattsmier, 1982c).
Quinine Quinine and other antimalarial drugs (e.g.,
quinidine, chloroquine, and hydroxychloroquine) have long
been known for their ability to produce temporary hearing
loss and tinnitus (e.g., Brummett, 1980; Brown et al.,
1981). With the decline of malaria in the United States,
however, these drugs have become infrequent sources of
tinnitus in this country, and as a consequence little has
-
been written about this form of tinnitus.
. . .
Quinine-induced
hearing loss and tinnitus are apparently of high fre-
quency, and the tinnitus onset reportedly precedes the
hearing loss.
While the hearing loss is reported to be
reversible in most cases, permanent loss has occurred--
apparently following large doses or protracted adminis-
tration. There appears to be a general belief that the
mechanism underlying the hearing loss and the tinnitus is
vasoconstriction, although the evidence is meager. Some
reports indicate that in sensitive individuals the quinine
contained in a single gin-and-tonic highball can be ade-
quate to produce tinnitus.
The occurrence of tinnitus following administration of
quinine sulfate is mentioned by Markham et al. (1967) and
Segal et al. (1974), and the danger to hearing of chloro-
quine phosphate is highlighted by the report of Dwivedi
and Mehra (1978). Chloroquine was shown to have an affin-
ity for melanin by Dencker et al. (1973), which makes that
compound, at least, different from salicylate.
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63
Tobacco Fowler (1942) asserted that smoking is a common
cause of tinnitus and that at least a month's cessation
is necessary to eliminate it as a causative factor.
Whether or not Fowler was correct in this belief has yet
to be satisfactorily established. Tyler (CIBA Foundation,
1981:235) indicates that new information on tobacco is
forthcoming.
Caffeine This agent is frequently mentioned for its
ability to produce or exacerbate tinnitus (e.g., CIBA
Foundation, 1981:235,263), but no systematic studies of
it were found.
Alcohol Alcohol has the curious characteristic of being
cited as both a cause and a treatment for tinnitus (see
"Alcohols in this chapter). Unfortunately, anecdotes are
the primary source of this information at this time (em.,
CIBA Foundation, 1981:201,268).
Cocaine Tinnitus is sometimes mentioned as a concomitant
to cocaine use, and its vasoconstrictive actions make this
claim believable. However, no information was found on
the dose levels needed, the time course of onset and
decline, etc.
Marijuana It has been asserted that marijuana can mark-
edly increase a preexisting tinnitus (CIBA Foundation,
1981:168), but no quantitative information appears to
exist.
Oral Contraceptives Some oral contraceptives can produce
a hearing loss and an associated tinnitus (Brown et al.,
1981). m e effects are thought to be due to vascular
changes. Detailed information was not found.
Heavy Metals Tinnitus is a common side-effect of heavy-
metal treatment for cancer (Merrin, 1978; Merrin et al.,
1978; Von Hoff et al., 1979) e For c~s-platinum at least,
the evidence indicates that the symptom is reversed upon
withdrawal of the drug.
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64
Drug Therapy for Tinnitus
~_., , ~
A wide variety of drugs have been investigated as possible
treatments for the symptom of tinnitus. The basis for
interest in a particular drug or class of drugs is fre-
quently not explicitly stated by the investigator, which
suggests that it came to attention simply because patients
receiving the drug for some other medical problem reported
their tinnitus to be alleviated. Given the general level
of ignorance about the sites of origin of and the mechan-
isms underlying tinnitus, this empirical origin of ideas
about tinnitus-alleviating drugs should not surprise us.
The fact is that greater success has been achieved with
drugs discovered in this way than with drugs studied
because of some theoretical view about the origins of
tinnitus.
The list of drugs investigated at one time or another
· . . . · . . · · . · ~
as a possible therapy against tinnitus is long (see
Goodey, 1981), and no attempt is made here to be exhaus-
tive. There are some general points about experimental
design that the reader ought to keep in mind while reading
the following synopses of the studies done on drug treat-
ment of tinnitus.
1. Because tinnitus is not a single entity produced by
a single or even a small number of causes, one should not
expect any one drug to be universally effective against
tinnitus. Further, the actual proportion of the sample
of patients reporting relief in a particular study will
depend heavily upon the makeup of that sample. If, for
some reason, an investigator ended up with a sample
heavily dominated by patients whose tinnitus arose from
the same problem--(say) in the cochlea itself--and if the
drug being studied proved to be extraordinarily effective
against that problem, that investigator might have a very
high success rate, while another investigator doing the
same manipulations, but on a sample less heavily dominated
by patients with that cochlear anomaly, might have a much
lower success rate. Even in those experiments in which
the audiological diagnoses on the patients are reported,
one cannot be confident about homogeneity in the site(s)
.
or origin of the tinnitus.
2. The severity of the tinnitus symptom varies greatly
across the patients used in different studies and some-
times across those in the same study. In some studies,
the patients used are referred to the investigator simply
because they have tinnitus, of whatever magnitude; in
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65
other studies, only severely afflicted patients are used
as subjects. Comparison of the success rates across
studies as different as these is problematic enough, let
alone trying to generalize to the population of tinnitus
sufferers at large.
3. Many of the drug studies of tinnitus do not include
the controls usually regarded as necessary for unambiguous
interpretation of an outcome. For example, few studies
utilize single- or double-blind procedures, control and
experimental groups, or cross-over designs.
4. Because of 2 and 3 above--the great heterogeneity
in the makeup of the patients in different drug experi-
ments and the absence of typical control procedures--it
is difficult to evaluate the contribution of the so-called
Hawthorne effect (Roethlisberger and Dickson, 1939) to the
reported success rates. When some of the patients have
been through months or years of frustration trying to get
relief from their tinnitus, it may be that anyone's doing
anything in an attempt to help them might be met with
reports of success.
5. It is very rare in drug studies of tinnitus for an
investigator to manipulate the dose level or the duration
of the administration, either within or across subjects.
Thus, the reader is always uncertain whether some of the
patients in the "no relief" category might have moved to
the "partial relief" category and/or some of the "partial
relief n to the "complete relief" category had the dosage
or the period of administration been changed.
6. Drug studies of tinnitus often do not include moni-
toring of, or reporting of, drug serum levels. This is
an understandable omission in many cases, since the taking
and analysis of numerous blood samples raises complica-
tions for both the patient and the experimenter. Without
such information, however, it is impossible to know
whether the difference between success and failure of
treatment in individual patients might be due to differ-
ential compliance with the dose schedule and/or differ-
ential absorption of the drug, for whatever reasons. It
is possible that some of the across-subject variability
in effectiveness of some drugs may be traced to different
"effective doses" reaching the relevant site, and while
drug serum level is an imperfect control for this prob-
lem, it does constitute a necessary first step. A pro-
cedure that seems sensible is one in which fixed or
weight-corrected doses are given to sufferers from a wide
variety of tinnitus types in the early experiments on a
particular drug, and then--given that there is some
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106
making recommendations is not clear. However, the absence
of residual inhibition is not taken as definite evidence
of lack of effectiveness of masking therapy (Vernon,
1981), and it does not invariably lead to the patient
being placed in the no-recommendation category (Vernon,
personal communication).
Not only are statistics about the relationship between
residual inhibition and recommendation category not avail-
able, but information about residual inhibition as a pre-
dictor of masker effectiveness is also lacking. For exam-
ple, the latest report summarizing follow-up data on 598
patients of the Oregon clinic (Schleuning et al., 1980)
does not present any correlations between residual inhi-
bition as measured on the standardized procedure and later
success with a tinnitus masker/instrument. It seems rea-
sonable to expect that the magnitude and duration of
residual inhibition will have at least some relation to
the magnitude and duration of the masker producing it.
The choices of 10 dB above masking level and 60 seconds
duration are not explained in detail and may be worthy of
further examination. Also of interest would be objective
data on the return of tinnitus magnitude following masker
termination--using (say) loudness matching of some sort
instead of verbal reports.
Some aspects of residual inhibition deserve further
study. It is commonly asserted that Feldmann (1971,
1981) frequently observed residual inhibition when the
masker was presented to the contralateral ear, while the
Oregon group never does (Vernon et al., 1977; Vernon and
Schleuning, 1978; Shulman, 1981:212). me truth appar-
ently lies somewhere in between. Vernon (personal com-
munication) claims that Feldmann observes contralateral
residual inhibition in only about 10 percent of his
patients and that that fraction is in good accord with
the experience of the Oregon group. Since the two groups
use maskers of markedly different intensity and duration,
this agreement is encouraging.
Vernon (CIBA Foundation, 1981:282; Vernon and Meikle,
1981) has noted that following a period of complete re-
sidual inhibition, some patients report that their tinni-
tus does not return gradually and monotonically, but
rather it "bounces back" in intermittent spurts; this
fact obviously has important implications for the under-
lying mechanisms.
Goodey (CIBA Foundation, 1981:288) has reported an
effect analogous to residual inhibition following drug
treatment of tinnitus. Upon withdrawal of a drug that
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107
has been effective against their tinnitus, about half the
patients find that the tinnitus never returns to its
previous level.
For the sake of completeness, the experience of Penner
(personal communication) with residual inhibition should
be noted. Recall that she works exclusively with patients
who are categorized as having sensorineural hearing loss.
In this select sample she finds that, following exposure
to the masker, about one-third report no change, about
one-third report decreased tinnitus (residual inhibition),
and about one-third report increased tinnitus. Recently,
the Oregon group also mentioned seeing increased tinnitus
following exposure in a substantial fraction of their
patients (Vernon and Meikle, 1981). The effect has been
named "residual facilitation, n but nothing about its
diagnostic value has been presented.
Safety of Tinnitus Maskers/Instruments
The concern most frequently expressed about tinnitus
maskers and instruments is that their use may be pro-
ducing hearing loss, or additional hearing loss. When
considering the problem of hearing loss induced by expo-
sure to intense sound, one must attend to several features
of the stimulating waveform (see Kryter et al., 1966):
its spectral makeup; its overall intensity and the dis-
tribution of intensity across the frequency regions
present' the duration of exposure; whether the exposure
sound is continuous or interrupted; and, if the latter,
the nature of the intermittence. In all applications
described to date, tinnitus maskers/instruments supply
continuous sound, so the contribution of intermittence to
exposure-induced hearing loss is a problem that can be
ignored for the time being. This leaves the issues of
the spectral characteristics, intensity, and duration of
the exposure, about which the following generalization is
relevant: for a noise with any given spectral charac-
teristics, the greater the intensity and/or the greater
the duration of daily exposure, the greater is the risk
of an exposure-induced hearing loss. The question, then,
is how great is the risk of wearing a tinnitus masker/
instrument?
Spectral Characteristics Many long-known and well-
documented facts of masking lead to the belief that the
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108
most efficient masker for a given sound--the one that will
require the least intensity--will be one that is located
in the same spectral region as, and has a bandwidth simi-
lar to (if a little wider than), that of the sound to be
masked. It must be remembered that, for the most part,
these basic data were collected on normal-hearing subjects
and that Feldmann (1971), Penner (1980), Penner et al.
(1981), and Vernon et al. (1980) have argued that at least
some forms of tinnitus do not behave in all respects like
"real" sounds when it comes to masking (see "Some Ways
Tinnitus Is Not Like an External Sounds in Chapter 3).
Nevertheless, explicitly stated goals of the masker/
instrument-fitting procedure are to determine and pre-
scribe the masking waveform that best masks the tinnitus
(Vernon et al., 1977; Vernon and Scheuning, 1978; Vernon
and Meikle, 1981). One obvious practical reason for these
goals is the belief that the narrower the bandwidth of the
tinnitus masker, the less interference it will produce
with the perception of important real-world sounds, such
as speech. But to date, these goals have been partially
frustrated by lack of availability of test equipment and
of tinnitus maskers/instruments capable of generating
waveforms with a wide variety of bandwidths and center
frequencies. In this regard, tinnitus test equipment has
improved more rapidly than have the tinnitus maskers/
instruments (Voroba, 1979b).
The spectral characteristics of several available tin-
nitus maskers were shown by Agnew (1979b) and Vernon and
Meikle (1981); while they do offer somewhat different dis-
tributions of intensity across frequency, all are quite
wideband in their outputs. This feature of present
maskers/instruments is troublesome in a number of ways.
Most obvious is that wide bandwidth maskers have more
potential to interfere with the perception of important
everyday sounds than do narrower maskers; this factor
acts to hold down the intensity at which the user sets
the masker/instrument and, thus, possibly diminishes its
effectiveness as a tinnitus masker. Second, all things
being equal, the more wideband the waveform is, the less
efficient a masker it will be. This factor acts to in-
crease the overall intensity at which the user sets the
masker/instrument, for the less efficient the masker is--
again, all things being equal--the greater its intensity
will have to be for a fixed level of masking. And, the
greater the intensity, the greater is the concern about
exposure-induced hearing loss.
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Two engineering aspects to the problem of individually
tailoring a masking waveform to a particular patient
deserve comment. One difficulty has been in the actual
delivery of high-frequency energy to the eardrum (the
high-frequency response of hearing aids has been simi-
larly limited by the lack of availability of small micro-
phones or speakers with efficient high-frequency re-
sponses). However, recent developments promise resolution
of this aspect of the problem; Killion (1981), for exam-
ple, has developed behind-the-ear and in-the-ear systems
having a nominal 16-kHz bandwidth. Utilization of these
systems in tinnitus maskers/instruments is to be encour-
aged.
The second aspect of the problem of individual tailor-
ing of tinnitus maskers involves the process of obtaining
the masker waveform. Until recently, the most common pro-
cedure for obtaining a narrow band of frequencies was to
begin with a relatively wideband source and then filter
out all frequencies but those in the spectral region of
interest. Filtering schemes have evolved over the years,
but it is still the case that a filter capable of supply-
ing a reasonably narrowband waveform at a high center
frequency is much too cumbersome to incorporate into an
everyday device such as a masker/instrument. And even if
this were possible, in order to permit true individual
tailoring of maskers, the manufacturers would have to make
available either a large number of devices with different
masker center frequencies or else a wide array of (say)
plug-in filter modules. An obvious solution to this prob-
lem is not to generate a wideband source and then filter
it to obtain a narrow band, but to generate a narrow band
in the first place. With digital synthesis and manipula-
tion of waveforms, such a possibility exists, but manu-
facturers of tinnitus maskers/instruments have yet to take
advantage of this approach. A small, easily wearable
device could be produced that is programmable by the manu-
facturer or the dispenser to generate a waveform with the
specific spectral characteristics determined to be neces-
sary to produce the most efficient masker of that pa-
tient's tinnitus--that is, a "master" tinnitus masker/
instrument. It is likely that the manufacturers have
(rightly) been cautious about developing such devices
because of uncertainty about the long-term efficacy of
masking for relief of tinnitus. The results reviewed
here suggest that such development may no longer be
premature.
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110
In regard to the issue of tailored narrowband maskers
for tinnitus, the reader is reminded of the pitch-matching
data of Penner and Voroba (see "Pitch Matching" in Chapter
3) implying that tinnitus frequency may vary greatly
across time. ~
If confirmed, this finding suggests Anal one
ideal tinnitus masker/instrument might be either narrow-
band but user-adjustable in frequency, or else just wide-
band enough to "cover" the frequency excursions of the
tinnitus of the particular patient.
Manufacturers contemplating development of new maskers/
instruments that capitalize on digital synthesis proce-
dures should be aware of recent evidence that indicts
waveforms with very steep spectral skirts (McFadden and
Pasanen, 1980; McFadden and Plattsmier, 1981a). Even if
subsequent reports do not confirm that such waveforms are
dangerous to the physiological mechanisms underlying fre-
quency resolution, they should still be avoided because
of their demonstrated ability to induce a short-term tin-
nitus (see "Possible Experimental Models of Tinnitus" in
Chapter 2), whose cumulative and long-term characteristics
are unknown. It would be ironic indeed if a new genera-
tion of tinnitus maskers/instruments were themselves
responsible for inducing additional tinnitus. The evi-
dence is still scanty, but it appears that narrowband
waveforms having attenuation rates of about -70 to about
-200 dB per octave at their "edges" are reasonably safe,
but that slopes of -400 dB per octave (McFadden and
Pasanen, 1980) and -600 dB per octave t~umm~s ana
Guttman, 1972) should be avoided.
, · ~
Intensitv of Tinnitus Maskers/Instruments and Duration of
. . .
Use On the basis of survey and experimental research on
the permanent hearing loss caused by sounds of various
, _ , _ _
~ ~ ~ _ :1 ~ ~ ~ _ _ 1~
intensities, durations, etc., so-called aamage/rlsK crl-
teria (DRC) have been established (Kryter et al., 1966).
For a fixed level of risk (proportion of population mani-
festing losses of particular magnitude at particular fre-
quencies), the DRC specify the combination of sound inten-
sity (measured on the "A-weighted" scale) and duration of
exposure that must not be exceeded during an 8-hour work
day in order to satisfy that risk criterion. For many
occupational purposes, the U.S. government has designated
90 dBA and lower as "safer for a working lifetime of daily
exposures (Occupational Safety and Health Administration,
1974). If the continuous noise exposure is 95 dBA, the
maximum allowable daily exposure is limited to 4 hours per
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111
day, and, if it is 100, 105, 110, or 115 dBA, the maximum
allowable daily exposures are 2, 1, 0.5, and 0.25 hours,
respectively. Ward et al. (1976), to take one example,
seem to view these as acceptably safe values, but some
investigators feel that a more conservative definition of
"safer--a "lower fence"--is necessary to adequately prom
teat workers. For example, Passchier-Vermeer (1974)
argues for 80 dBA for steady-state noises and daily 8-hour
exposures (also see Burns and Robinson, 1970; Berger et
al., 1978). Obviously, if the exposures are for periods
greater than 8 hours or for more than 5 days per week,
the specified intensities would have to be correspond
ingly decreased in order to maintain the same average
loss of hearing. This is an important point, for appar-
ently many users of tinnitus maskers/instruments wear
them throughout their waking hours (Vernon and Meikle,
1981), and some even sleep with them on. (Contrary to
general expectation, perhaps, is the fact that only about
one-half of the people with serious tinnitus have diffi-
culty falling asleep, and this seems to bear no simple
relationship to the matched intensity of the tinnitus
[see Vernon, 1977].) Thus, it is not possible to reach a
decision about the safety of tinnitus maskers/instruments
by simply comparing their maximum overall intensities with
the standard damage/risk criteria--longer daily exposures
and more successive days per week are involved.
A report issued by the U.S. Environmental Protection
Agency (1974) includes procedures for translating the
8-hour occupational standards into corresponding levels
for 24-hour exposures. As noted above, an important con-
sideration is the intermittence of the exposure. Let us
first consider an extreme, hypothetical cas~-a patient
who uses a tinnitus masker/instrument continuously at the
same level throughout each 24-hour period. For this no-
intermittency situation, the translation procedure yields
a value of 66.4 dB as the maximum permissible (in order
to protect virtually every person from more than 5 dB of
permanent hearing loss at 4000 Hz after 40 years of ex-
posure). If the hypothetical patient did not keep the
masker adjusted to the same level throughout the 24-hour
period, but occasionally reduced its level or turned it
off--that is, introduced intermittency--then the maximum
permissible level could be greater than 66.4 dB. To take
one example, assume that for at least 10 percent of each
1-hour period the patient sets the masker level to 65 dBA
or less; the maximum permissible level now rises to 71.4
dB. The maximum permissible level rises to 73 dB if the
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112
masker is continuous for only 8 consecutive hours per day
and is 60 dB or less for the remaining 16 hours. Various
other examples are possible but are not necessary for cur-
rent purposes. We see that somewhere in the vicinity of
66 to 73 dBA would be the maximum allowable level of a
tinnitus masker that was worn regularly if existing
damage/risk criteria were the relevant standard for regu-
lation. It is to this range of levels, then, that one
might want to compare the levels typically experienced by
wearers of tinnitus maskers/instruments. Unfortunately,
the comparison is not easily made, given the available
data. (It must be emphasized that these EPA translations
are viewed as unnecessarily conservative by many experts
who believe that "effective quiet" may lie at or somewhere
above 75 dB. Without getting into this controversy, it
can be noted that, even if the safe level for continuous
24-hour exposure were to rise by, say, 15 dB from the
66-73-dBA range cited, none of the following arguments
would be qualitatively altered.)
When dealing with pathological ears, the standard way
to express sound level is relative to the patient's abso-
lute sensitivity (absolute threshold) for that sound in
that ear; sound levels so referenced are designated as
decibels sensation level (dB SL). This usage is sensible
for many purposes, for it often better communicates a
sense of stimulus strength, or perceptual magnitude, in
pathological ears than does a unit with a fixed reference
such as decibels sound-pressure level (dB SPL). m e prob-
lem this raises for us, however, is that DRC, effective
quiet, etc., traditionally are specified in units analo-
gous to dB SPL, while the intensities necessary to mask a
tinnitus are typically given in dB SL without the neces-
sary information to make the transformation to dB SPL.
Thus, while we know from numerous reports that the meas-
ured loudness of tinnitus is typically low--only rarely
is it matched to sounds greater than about 20 dB SL (see
"Magnitude of the Tinnitus" in Chapter 3)--we do not know
the overall sound-pressure level typically necessary to
mask it. About all we presently have to go on when evalu-
ating the safety of tinnitus maskers/instruments is the
manufacturers' specifications of maximum level.
The manufacturers' specifications sheets for many
models of tinnitus masker state a minimum overall output
level of 40-45 dB SPL (note, not "A-weightedn) and a maxi-
mum overall output level of between 85 and 95 dB SPL, and
some models specify maxima in the range of 105-110 dB
SPL. mese measurements are sometimes made using a stan
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113
card 2-cc coupler (e.g., HA-1), but they are frequently
also made using a Zwislocki coupler (with the dB 110
adapter), which better reflects the high-frequency char-
acteristics of the typical ear canal. This latter pro-
cedure is to be preferred, particularly when dealing with
maskers/instruments specifically designed to mask high-
frequency tinnitus, for the standard coupler underesti-
mates the level of high frequencies.
Therefore, essentially every masker/instrument now
available is capable of producing sound levels in excess
of the 66-73 dBA that is derived as safe from existing
standards, and some are capable of producing levels far
in excess of that value. (Recall that current OSHA regu-
lations would allow only about 0.5 hour per day per 5-day
week of the 110 dB that some maskers/instruments claim to
be capable of.) Thus, the potential for damage, or addi-
tional damage, to hearing clearly exists. At this time
it is impossible to estimate how much risk is involved--
or how much damage has already been done--because there
are no systematic data yet available on the levels at
which satisfied, chronic users of maskers/instruments
routinely set their devices, on the temporal patterns of
use, or on changes in hearing sensitivity after prolonged
use of these devices. It may be that the typical user
sets the masker/instrument to a level below the nominal
66-73 dBA or sets it to different values throughout the
day, thereby reducing the overall risk. Data on these
issues are important to acquire, and, given the large and
growing number of users of maskers/instruments, they
should not be difficult to obtain. People with bilateral
hearing loss but monaural tinnitus would be particularly
interesting, since the nontinnitus ear would serve as a
within-subjects control for additional loss.
It should be noted that, if manufacturers do begin pro-
ducing tinnitus maskers/instruments capable of generating
narrowband waveforms, it will raise a further complication
to the use of existing DRC and other guidelines as stan-
dards for regulating maskers/instruments. Most of what
is known about exposure-induced hearing loss comes from
exposures to relatively broadband waveforms, and it is
that knowledge upon which DRC have been based. However,
concentrating all the energy in a relatively narrow
spectral region can create a potentially more damaging
waveform than one with the same overall level but greater
bandwidth. The magnitude of the additional risk is
unknown, however. For such noises EPA guidelines in dBA
are not appropriate, and criteria for octave or one-third
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114
octave bands such as those described by Kryter et al.
(1966) should be used. To the extent that tinnitus
behaves like an external sound when it comes to masking
(cf. Feldmann, 1971; Vernon et al., 1980; Penner et al.,
1981), the narrowband masker is to be preferred, for the
overall level required to achieve masking of the tinnitus
with a narrowband waveform should be lower than that re-
quired with a wide one--with external sounds it is the
spectrum level that matters for masking, not the overall
level. Even when the tinnitus does not act like an ex-
ternal signal, the narrowband masker has a virtue: it
puts a smaller segment of the basilar membrane at risk of
damage than does a wider-band masker. While there is
some knowledge about the relative dangers of noise bands
of different center frequency (Kryter et al., 1966),
almost nothing is known about frequency regions above
about 4000 Hz, so, if narrowband tinnitus maskers are
developed for use at very high frequencies, existing DRC
will be of questionable applicability.
Damage/Risk Criteria and Tinnitus Maskers/Instruments
Much of the above discussion may be irrelevant. It is
extremely important to appreciate that compliance or
noncompliance with current or future DRC may not be an
appropriate basis on which to judge or to regulate tin-
nitus maskers/instruments. For many people, tinnitus is
a severe, debilitating affliction, and it could easily be
argued that relief from this affliction is, in many cases,
worth the risk, or even the inevitability, of some hearing
loss. Many commonly used drugs carry risks (or inevit-
abilities) of negative effects of various sorts, and even
hearing aids themselves are capable of producing sound
levels far in excess of both the 66-73-dBA and the 90-dBA
values cited, depending upon the ambient levels in which
the user lives. m e implicit risks attendant to the use
of such drugs, and of hearing aids, are generally judged
by medical professionals, laymen, and users to be worth
the benefits accrued. Tinnitus maskers/instruments
appear to be indistinguishable from common drugs and
hearing aids in this regard. That is, it can be argued
that, if tinnitus sufferers are made aware of the poten-
tial risks to hearing involved in using a tinnitus masker/
instrument at high intensities and/or for prolonged pe-
riods of time, and they still choose to wear the device,
perhaps that decision should be theirs to make. It is
clear that in the past "the consent" of masker/instrument
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115
users has not been as "informed" as it might have been,
but this is true for users of hearing aids as well, and
the solution appears simple. m e practitioner, the dis-
penser, or the manufacturer could supply a brief written
document that explains the situation and emphasizes the
virtues of always using as weak a masker as possible and
of introducing as much intermittence as possible (advice
that seems equally desirable for users of hearing aids).
In this regard, the outcome of Penner et al. (1981)
should be recalled; for some forms of tinnitus, continu-
ous maskers lose their effectiveness relatively rapidly,
and increasingly higher sound levels are necessary to
accomplish the same result. Regular intermittence in the
use of the tinnitus masker/instrument worn by such people
would appear to be highly desirable.
-
The ability to use
lower masker levels ought to make the masker/instrument
less obtrusive for the wearer, and it certainly ought to
reduce the risk of masker-induced hearing loss. At this
time no systematic studies have been done on the period-
icity and duration of the intermittence necessary to
control masker level in these patients.
Related to this matter of intermittence is another
point. It might be possible to capitalize on the residual
inhibition effect to gain greater safety and reduced in-
convenience in tinnitus maskers/instruments. A member of
the Working Group (L. Kaufman) realized that for some
people it might be possible to periodically interrupt or
to amplitude-modulate (AM) the masker wave-form at a rate
that would allow residual inhibition to tide the person
over until the next masker interval (or half-cycle of high
intensity). me basic idea, of course, is to have the
masker present only long enough and at adequate intensity
to institute a subsequent period of residual inhibition.
Interruption or AM rates of about two cycles per minute
ought to be about right, according to the residual inhibi-
tion evidence reported by the Oregon group. The advan-
tages to the user would be that: (1) about half the time
the masker would be at a low level or absent and thus
should be less of an impediment to the processing of real-
world sounds such as speech, and
(2) as a consequence,
the average daily noise exposure would be reduced.
The
variants of the idea that come to mind appear to require
more elaborate hardware than does simple AM, but obviously
other temporal sequences of masker level would be possible
with microprocessor-based maskers/instruments. Presum-
ably, relatively long rise-decay times would always be
important. A possible problem is that a slowly varying
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116
or regularly intermittent masker might be more annoying
than a steady one, but the idea is definitely worth try-
ing with some patients for whom residual inhibition is
strong.
Hearing professionals have had a long-standing concern
about the possibility that hearing aids induce additional
hearing loss (sometimes known as induced deterioration or
overamplification). Berry (1939) and Holmgren (1939) were
among the first to raise the issue, which has yet to be
satisfactorily resolved. To cite just a few of the pub-
lished papers on the topic, Kinney (1961), Macrae and
Farrant (1965), and Jerger and Lewis (1975) all concluded
that there is evidence for temporary or permanent deter-
ioration of hearing induced by hearing aids set for high
amplification, while Naunton (1967), Bellefleur and Van
Dyke (1968), Derbyshire (1976), and Titche et al. (1977)
all concluded the opposite. A reading of this literature
makes it believable that the disagreement stems in part
from lack of adequate control of such important factors
as actual level of amplification of the aid, length of
its use, type of impairment, measurement procedures, and
ambient environmental levels. In a recent article, Humes
and Bess (1981) argue that--even using very conservative
estimates of such critical factors as exposure level and
duration--most hearing-aid users probably are at risk of
substantial additional hearing loss from daily use of
their aids. Weir calculations are worthy of careful
study by anyone interested in this important problem.
For our purposes here, it must be concluded that, while
the safety aspects of tinnitus maskers/instruments would
appear to have much in common with those of hearing aids,
too little is known about the latter to help us reach a
decision about the former.
Representative terms from entire chapter:
residual inhibition
