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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
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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 .) 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.  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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109 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: