An Assessment of Threshold Shifts in Nonprofessional Pop/Rock Musicians Using Conventional and Extended High-Frequency Audiometry

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1 An Assessment of Threshold Shifts in Nonprofessional Pop/Rock Musicians Using Conventional and Extended High-Frequency Audiometry Nicolas Schmuziger, 1,2 Jochen Patscheke, 1 and Rudolf Probst 1,3 The clinical value of extended high-frequency audiometry for the detection of noise-induced hearing loss has not been established conclusively. The purpose of this study was to assess the relative temporary threshold shift (TTS) in two frequency regions (conventional versus extended high frequency). In this exploratory study, pure-tone thresholds from 0.5 to 14 khz were measured in both ears of 16 nonprofessional pop/rock musicians (mean age, 35 yr; range, 27 to 49 yr), before and after a 90-minute rehearsal session. All had experienced repeated exposures to intense sound levels during at least 5 yr of their musical careers. After the rehearsal, median threshold levels were found to be significantly poorer for frequencies from 0.5 to 8 khz (Wilcoxon signed rank test, p < 0.004) but were unchanged in the extended high-frequency range from 9 to 14 khz. Decreases in the median threshold values measured before the rehearsal were present across the conventional frequency range, most notably at 6 khz, but were not observed in the extended highfrequency range. On the basis of these results, extended high-frequency audiometry does not seem advantageous as a means of the early detection of noise-induced hearing loss. (Ear & Hearing 2007;28; ) Noise-induced hearing loss (NIHL) after longterm exposure to broadband noise has a characteristic audiometric pattern with a notch in the 3- to 6-kHz range, which has been related to the primary resonant frequency of the external auditory canal (Rodriguez & Gerhardt, 1991). However, limitations in the specificity and sensitivity of the association of such a notched audiometric configuration with NIHL have been reported (Fausti, Erickson, Frey, et al., 1981; Schmuziger, Fostiropoulos, & Probst, 2006). For example, inner ear damage caused by middle ear infections or by inherited predispositions may demonstrate similar audiometric contours. The goal of hearing conservation programs is to detect changes of the cochlea induced by noise as early as possible. One question is whether or not 1 Department of Otorhinolaryngology, University Hospital, Basel, Switzerland; 2 Department of Otorhinolaryngology, Cantonal Hospital, Liestal, Switzerland; and 3 Department of Otorhinolaryngology, University Hospital, Zürich, Switzerland. pure-tone audiometry in the conventional frequency range is a sensitive method for this purpose. Several findings would argue in favor of using the extended high-frequency range as a possible addition or alternative. One such finding was the identification of significantly lower air-conduction thresholds above 8 khz in the African Mabaans presumably representing a population with particularly low noise exposure compared with age-matched control subjects (Rosen, Plester, El-Mofty, et al., 1964). Additionally, extended high-frequency audiometry is often successful at detecting ototoxicity from aminoglycosides and cisplatin before there is an effect on the frequency range that typically occurs in conversational speech (Fausti, Henry, Helt, et al., 1999). A similar mechanism may be operating when the cochlea is altered from noise exposure. It has been shown that the mechanisms of sensory hair cell degeneration in response to noise and aminoglycosides share a final common pathway (Cheng, Cunningham, & Rubel, 2005), which may be an argument for similar effects of intense noise and ototoxic drugs on the cochlea. Several hydrodynamic effects have been proposed as possible contributors to the vulnerability of the base of the cochlea to noise. These effects include a) greater traveling wave amplitude at the base, b) greater acoustic load at the base, and c) a possible basal locus for shock from impulse energy abnormally conducted to the cochlea (Fausti, Erickson, Frey, et al., 1981). Extended high-frequency audiometry measures hearing thresholds for pure tones from 8 to 16 khz, according to ISO (1998). Testing in this frequency range has technological limitations. Complex physical interactions of high-frequency pure tones in the ear canal can result in standing waves that might increase intra- and intersubject variability of hearing thresholds in the affected frequency range. When a sound impinges on the tympanic membrane, some of the energy is reflected back. The interaction between the reflected and incident waves creates standing waves with pressure maxima and minima at different points along the ear canal (Stinson, 1985; Stinson, Shaw, & Lawton, 1982). 0196/0202/07/ /0 Ear & Hearing Copyright 2007 by Lippincott Williams & Wilkins Printed in the U.S.A. 643

2 644 SCHMUZIGER, PATSCHEKE, AND PROBST / EAR & HEARING, VOL. 28, NO. 5, Although normative data for pure-tone thresholds in the conventional frequency range are widely available (e.g., ISO 7029, 2000), this is not the case for the extended frequency range. Frank (1990) concluded that normative thresholds in the extended high-frequency range could not be recommended for clinical use in individual subjects due to the large intersubject threshold variability. For group means, this does not seem to be a serious issue (own unpublished observations; Sakamoto, Sugasawa, Kaga, et al., 1998; Stelmachowicz, Beauchaine, Kalberer, et al., 1989). Normative data that may be used for comparison of individual test results for this frequency range must be collected separately by each test site. Studies on the use of extended high-frequency testing for purposes of detection of NIHL have reported conflicting findings. Schmidt, Verschuure, & Brocaar (1994) found similar pure-tone threshold levels in the extended high-frequency range for conservatory students in comparison to a reference group. In contrast, other cross-sectional studies have suggested changes in pure-tone thresholds in the extended-high frequency range after repeated exposure to high-level sounds (e.g., Fausti, Erickson, Frey, et al., 1981; Hallmo, Borchgrevink, & Mair, 1995). These studies have not investigated the time course of the NIHL as a function of frequency; that is to say, which frequencies are affected first. In comparison to a cross-sectional study design, a longitudinal study design is more sensitive for examining the effects of noise exposure. The hearing function of adolescents who have been repeatedly exposed to high sound levels during recreational activities has been recently examined over a 4-yr period (Biassoni, Serra, Richter, et al., 2005; Serra, Biassoni, Richter, et al., 2005). Hearing thresholds were elevated particularly in the higher frequencies, which was attributed to the effects of the recreational noise exposure. However, a control group was lacking in these analyses, and the exclusion criteria were poorly defined. One difficulty of assessing nonoccupational noise-induced hearing loss is that the levels and durations of the noise exposure are unknown. There is also no control of individual susceptibility (Henderson, Subramaniam, & Boettcher, 1993). It is noteworthy that Job, Raynal, & Rondet (1999) investigated the effects of personal stereo use in young adults and found that hearing threshold elevations could be demonstrated only in subjects with a history of recurrent otitis media in childhood. Lee, Matthews, & Dubno et al. (2005) recently published results from a longitudinal study of puretone thresholds in the conventional and extended high-frequency range in 188 older adults over a period of 3 to 11.5 yr. The average rate of change in pure-tone thresholds was 0.7 db per year at 0.25 khz, increasing gradually to 1.23 db per year at 12 khz. The rates of threshold change for subjects with a positive history for noise exposure were not statistically different from those with a negative noise history. Kuronen, Sorri, & Paakkonen et al. (2003) used both conventional and extended high-frequency audiometry to measure pure-tone thresholds in military pilots after they had completed a single flight. The duration of the noise exposure was approximately 60 minutes. The noise levels at the inlet of the ear canal were rather moderate, with approximately 90 dba equalized sound pressure levels (1-hr L eq ). The authors reported statistically significant but clinically minor threshold shifts both in the conventional and extended high-frequency ranges. Particularly, there were no significant differences distinguishing the extended high-frequency range as being more sensitive to the changes. In summary, conclusions are not definitive concerning the extent and time-course of the effects of noise-induced cochlear damage on extended highfrequency thresholds. In part, the findings are limited because of the variables discussed. We have demonstrated in our laboratory that short-term intraindividual test repeatability is good in the extended high-frequency range from 8 to 14 khz and that it is comparable with test repeatability in the conventional frequency range (Schmuziger, Probst, & Smurzynski, 2004). Therefore, from a methodological point of view, temporary threshold shift (TTS) tests with threshold measurements both in the conventional and extended high-frequency range would reliably assess possible noise-induced TTS across the frequency range from 0.25 to 14 khz. Our study was intended to determine if noise has a preferential effect on the extended high-frequency range in a controlled noise exposure, similar to the study design of Kuronen, Sorri, Paakkonen, et al. (2003). Although temporary threshold shift (TTS) is not a good predictor of permanent threshold shift (PTS) (Henderson, Subramaniam, & Boettcher, 1993), its measurement still represents the only ethical method with sufficient control for developing information regarding the effects of noise on human hearing (Melnick, 1991). SUBJECTS AND METHODS Subject Inclusion and Exclusion Criteria The inclusion criteria that we adopted for the musicians in this study were: the musical activity had to be nonprofessional in nature (the main income of each subject had to be derived from nonmusical activities), each individual had to be a

3 SCHMUZIGER, PATSCHEKE, AND PROBST / EAR & HEARING, VOL. 28, NO. 5, member of a pop/rock band for 5 yr or more, and all subjects were required to have at least a weekly 2-hr exposure to intense sound levels from electroamplified music. With the exception of recreational noise exposures, the exclusion criteria for the study subjects were those that had been previously determined for the Questionnaire for Hearing Tests (ISO/ TC43/WG1, 1996). These included a) any occurrence of acoustic trauma, b) excessive noise exposure during occupational activities, c) a history of recurrent otitis media, d) previous ear surgery, e) fractures of the cranium, f) ingestion of potentially ototoxic drugs, and g) a report of hearing difficulties within the family except for presbycusis. All musician subjects had normal otoscopic findings and screening immittance measurements. Informed consent was obtained from all subjects participating in the study, according to the guidelines approved by the Ethics Committee, University Hospital of Basel. Subjects Sixteen subjects (2 women, 14 men) ranging in age from 27 to 49 yr, with a mean age of 35.5 yr (SD, 6.8 yr) met the inclusion criteria. Their instruments included guitar (N 4), bass (N 5), percussion (N 4), keyboard (N 2), and there was one vocalist (N 1). An amplified instrument or voice was the primary source of noise for all musicians with the exception of the four percussionists. The average weekly exposure of these musicians to broad band noise stimuli at intense sound levels by electroamplified music was approximately 5 hr (SD 2 hr, range 2 to 13 hr), over a mean period of approximately 17 yr (SD 8 yr; range 5 to 30 yr). Subjects did not wear ear protection during their rehearsals. Sound Level Measurements Sound level measurements (A-weighted, equalized, and maximal sound levels, L eq and L max, respectively) were taken close to the ear of each subject during the rehearsal using a Brüel & Kjaer (B & K) 2231 Sound Level Meter, with ab&k7100 Application Module and a B & K 4145 free-field microphone. A B&K 4230 Sound Level Calibrator was used to calibrate the sound level meter. Procedure A digital, PC-controlled audiometer (Insider of Audiocare, Switzerland) that was equipped with circumaural Sennheiser HDA 200 earphones was used for testing. The audiometer was calibrated according to the manufacturer s instructions. According to IEC (1994), the frequency of 8 khz is considered to be both the highest frequency in the conventional range and the lowest frequency in the extended high-frequency range. In this study, the 8 khz frequency was considered to belong to the conventional range, to avoid possible ambiguities. We have recently demonstrated that reproducibility is significantly poorer in the highest frequency range at 16 khz (Schmuziger, Probst, & Smurzynski, 2004). Moreover, informal testing (unpublished data) has shown that low frequency distortion occurs in particular when test tones at 16 khz are presented at high levels. Hence, we limited the extended high-frequency range to 14 khz. Hearing thresholds were determined using a modified Hughson Westlake technique. Baseline thresholds before the rehearsal were obtained after a non-noise-exposed period of at least 36 hr. Subsequent threshold measurements started approximately 20 minutes after the rehearsal for every subject. The order of presentation of frequencies was: 9, 10, 11.2, 12.5, 14, 0.5, 1, 2, 3, 4, 6, and 8 khz, and the tests were counterbalanced across right and left ears to avoid an order effect. This frequency sequence was selected so that priority could be given to the frequency range of interest. For practical reasons, it was not possible to test the musicians immediately after the rehearsal (e.g., 2 minutes after their exposure). Subjects were transported individually from the rehearsal site to our laboratory, which contained a sound-treated booth meeting the ambient noise level requirements of ISO (1989). Transportation time was approximately 15 minutes. This did not allow small TTSs that might have occurred in the first 20 minutes to be detected. However, the purpose of the study was to determine changes in threshold relative to frequency ranges rather than the magnitude of the shifts. Analysis Statistical procedures were performed using SigmaStat software (version 3.0) according to the recommendations of a professional statistician. Because the data were not always normally distributed, nonparametric statistical tests were used. For paired data, the Wilcoxon signed-rank test was performed. RESULTS Sound Level Measurements The exposure time to loud music during the rehearsals was 90 minutes for all subjects. The equalized sound levels during the rehearsals ranged from to dba 1.5-hr L eq, with a mean of dba 1.5-hr L eq, as measured at the entrance to

4 646 SCHMUZIGER, PATSCHEKE, AND PROBST / EAR & HEARING, VOL. 28, NO. 5, Fig. 1. Pure-tone thresholds (db HL) in the frequency range from 0.5 to 14 khz for both ears of the 16 subjects are displayed as box plots for each frequency both before and after a 90-minute rehearsal session. The horizontal line through each box denotes the median value, boxes indicate the quartile ranges, and whiskers denote 90th and 10th percentiles. the subjects ear canals. The maximal sound levels ranged from to dba, with a mean of dba. Further analysis demonstrated similar sound levels for the subgroup of percussionists compared with the other musicians (maximal sound levels, mean 110 versus dba; equalized sound levels, mean 102 versus dba 1.5-hr L eq ). Thresholds Pure-tone thresholds for both ears of the 16 subjects both before and at between 20 to 40 minutes after the rehearsal are shown in Figure 1. The median thresholds after the rehearsal were found to be elevated as follows: 5 db for 0.5, 1, 1.5 and 8 khz; 7.5 db for 2, 3 and 6 khz; 10 db for 4 khz, 0 db for 9 to 12.5 khz; and 2.5 db for 14 khz. Statistical analysis without Bonferroni correction using the Wilcoxon signed-rank test yielded the following results: p for 0.5, 1, 2, 3, 4, 6, and 8 khz; p for 1.5 khz and p 0.05 for the tested frequencies in the extended high-frequency range at 9, 10, 11.2, 12.5, and 14 khz. Further analysis demonstrated similar TTS for the subgroup of percussionists compared with the other musicians. However, the percussionists showed a more pronounced dip of 5 to 10 db from 3 to 6 khz in the averaged pure-tone results obtained before the rehearsal when compared with the averaged audiogram of the other musicians. The duration of noise exposure and the age were similar for both groups. DISCUSSION Extended high-frequency audiometry is a suitable method for the early detection of ototoxicity, but its clinical potential for the early detection of noiseinduced hearing loss is uncertain. In this study, we found significant threshold shifts in the conventional frequency range in a cohort of amateur pop/ rock musicians after a rehearsal of 90 minutes but no shift in the extended high-frequency range. Sound levels during this rehearsal were approximately 100 to 105 dba 1.5-hr L eq, which is well above the minimum sound pressure level of approximately 75 dba required to produce TTS (Feuerstein, 2002). Our results of noise-induced threshold shifts in the conventional frequency range are in agreement with results from previous studies using conventional audiometry and demonstrate a maximum TTS effect at 3 to 6 khz for broad-band stimuli (Melnick, 1991). In comparison to our results, Kuronen, Sorri, Paakkonen, et al. (2003) measured somewhat lower noise exposure levels in the cabins of different military aircraft during an exposure time of approximately 1 hr. In addition, all of the pilots involved in their study had been wearing a helmet and the measured noise levels at the ear s entrance were lower by approximately 10 db than the measured cabin noise levels. The estimates of average TTS ranged from 0 to 2.3 db in the conventional frequency range and from 1.2 to 3.5 db in the extended high-frequency range. This was statistically significant for several frequencies from both ranges. However, from a clinical point of view these changes were minor. In contrast, from our current analyses of nonprofessional musicians who used no ear protection, we have found both statistically and clinically significant noise-induced threshold shifts in the conventional frequency range but not in the extended high-frequency range from 9 to 14 khz. Further analysis of our data revealed similar TTS for percussionists in comparison to the other musicians, where the amplified instrument or voice was the primary source of noise. Particularly, TTS could be demonstrated in the conventional frequency range, but not in the extended high-frequency range. In the pretest, the percussionists had poorer hearing sensitivity at 3 to 6 khz than did the other musicians. This is in agreement with the literature (Axelsson, Eliasson, & Israelsson, 1995), indicating that impulsive noise is potentially more harmful than steady-state noise. A noise-induced PTS occurs when there is less than a full recovery from a noise-induced TTS. This may be a fairly common occurrence, with small amounts of permanent damage taking place after multiple TTS experiences (Feuerstein, 2002). If these considerations are valid, then we may not expect PTS in the extended high-frequency range from 9 to 14 khz, because TTS did not occur in this frequency range for the subjects in this study. Fur-

5 SCHMUZIGER, PATSCHEKE, AND PROBST / EAR & HEARING, VOL. 28, NO. 5, thermore, because there is currently no international standard that provides descriptive statistics for hearing thresholds in the extended high-frequency range in otologically healthy populations of various ages, we are not able to address the issue fully of whether the median thresholds of the audiogram before the rehearsal from 9 to 14 khz are normal. Not even carefully obtained data from matched control subjects would be sufficient to answer this question because the sample size is not large enough. However, median thresholds of 5 db HL at 9 and 10 khz, and of 10 db HL at 11.2 and 12.5 khz, argue against a significant hearing loss in our subject group, particularly if the age of the subjects is taken into account. In contrast, a median threshold of 30 db HL at 14 khz seems to be somewhat higher when compared with age-matched audiometric data previously obtained in our laboratory when assessing test-retest reliability at 0.5 to 16 khz on 138 subjects in the 12- to 51-yr age range (Schmuziger, Probst, & Smurzynski, 2004). CONCLUSION In this study, a significant TTS was found in the conventional frequency range from 0.5 to 8 khz, but no TTS was observed in the extended high-frequency range from 9 to 14 khz in a cohort of amateur pop/rock musicians after exposure to intense, continuous-type sound levels during a 90- minute rehearsal. Cross-sectional analysis of the data obtained before the rehearsal revealed a significant PTS at 3 to 8 khz but no evidence for a relevant PTS at 9 to 12.5 khz for these subjects who have had average weekly exposures to intense sound levels by electroamplified music of approximately 5 hr over a mean period of approximately 17 yr. Moreover, the evidence for a small PTS at 14 khz was weak. These latter findings must be treated with caution due to the relatively small sample size. ACKNOWLEDGMENTS This study was supported by grants from the Swiss Federal Office for Public Health. We are grateful to Dr. Kilian Perrem and Dr. Frances P. Harris, who provided helpful comments during the writing of this article. We thank Dr. Christian Schindler for his advice on statistical analyses, which was greatly appreciated. Address for correspondence: Dr. Nicolas Schmuziger, HNO- Klinik, Kantonsspital Liestal, CH-4410 Liestal, Schweiz. nschmuziger@vtxmail.ch. Received November 29, 2005; accepted March 23, REFERENCES Axelsson, A., Eliasson, A., Israelsson, B. (1995). Hearing in pop/rock musicians: A follow-up study. Ear and Hearing, 16, Biassoni, E. C., Serra, M. R., Richtert, U., Joekes, S., Yacci, M. R., Carignani, J. A., et al. (2005). 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