J Am Acad Audiol 24:992–1000 (2013)
Diagnostic Pure-Tone Audiometry in Schools: Mobile Testing without a Sound-Treated Environment DOI: 10.3766/jaaa.24.10.10 De Wet Swanepoel*†‡ Felicity Maclennan-Smith* James W. Hall*
Abstract Purpose: To validate diagnostic pure-tone audiometry in schools without a sound-treated environment using an audiometer that incorporates insert earphones covered by circumaural earcups and real-time environmental noise monitoring. Research Design: A within-subject repeated measures design was employed to compare air (250 to 8000 Hz) and bone (250 to 4000 Hz) conduction pure-tone thresholds measured in natural school environments with thresholds measured in a sound-treated booth. Study Sample: 149 children (54% female) with an average age of 6.9 yr (SD 5 0.6; range 5 5–8). Results: Average difference between the booth and natural environment thresholds was 0.0 dB (SD 5 3.6) for air conduction and 0.1 dB (SD 5 3.1) for bone conduction. Average absolute difference between the booth and natural environment was 2.1 dB (SD 5 2.9) for air conduction and 1.6 dB (SD 5 2.7) for bone conduction. Almost all air- (96%) and bone-conduction (97%) threshold comparisons between the natural and booth test environments were within 0 to 5 dB. No statistically significant differences between thresholds recorded in the natural and booth environments for air- and bone-conduction audiometry were found ( p . 0.01). Conclusions: Diagnostic air- and bone-conduction audiometry in schools, without a sound-treated room, is possible with sufficient earphone attenuation and real-time monitoring of environmental noise. Audiological diagnosis on-site for school screening may address concerns of false-positive referrals and poor follow-up compliance and allow for direct referral to audiological and/or medical intervention. Key Words: Air conduction, bone conduction, diagnostic audiometry, hearing screening, school-entry screening Abbreviation: NHS 5 newborn hearing screening
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evelopmental and socioeconomic benefits of early detection of hearing loss, primarily through newborn hearing screening (NHS) programs, are now widely established and accepted (American Academy of Pediatrics, Joint Committee on Infant Hearing [JCIH], 2007). Despite the success of NHS programs, a significant number of permanent moderate or greater bilateral and unilateral impairments are only identified around the time of school entry (Bamford et al, 2007; American Academy of Audiology [Academy], 2011). This is attributed to several reasons including (1) NHS screen technologies targeting hearing loss of 30 to 40 dB omitting screening
for low-frequency hearing loss; (2) not all infants referred from NHS receive diagnostic services; and (3) the occurrence of late-onset, acquired, or progressive losses (Bamford et al, 2007; Academy, 2011). In developing countries where NHS programs are scarce, school-based screening may also be the first opportunity to identify hearing loss (Olusanya et al, 2007). According to Fortnum and colleagues (2001), for every 10 children identified with permanent bilateral hearing loss greater than 40 dB through NHS, an additional five to nine children will present with similar hearing loss by the age of 9 yr.
*Department of Communication Pathology, University of Pretoria, South Africa; †Ear Sciences Centre, School of Surgery, University of Western Australia, Nedlands, Australia; ‡Ear Science Institute Australia, Subiaco, Australia De Wet Swanepoel, Ph.D., Department of Communication Pathology, University of Pretoria, C/o Lynnwood and University Roads, Hatfield, 0002, South Africa; E-mail: [email protected]
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Based on current evidence, the American Academy of Audiology (2011) has recommended preschool and schoolbased hearing screening for permanent hearing loss and longstanding and frequently recurring conductive hearing loss, which may impact linguistic development and school performance. This is proposed as a critical strategy toward optimal academic outcomes for children with possible long-term economic savings. The recommended approach for school-based screening has remained pure-tone audiometry as first-stage screen (American Speech-Language-Hearing Association [ASHA], 1997; Bamford et al, 2007; Academy, 2011). While tympanometry screening may target screening for middle ear disorders, like otitis media with effusion, it is usually recommended as a second-stage screen after a puretone audiometry refer result (ASHA, 1997; Academy, 2011; Bamford et al, 2007). One of the most significant and persistent problems faced by school-based screening programs are high referral rates. A summary of UK-based school-entry screening indicated a median referral rate of 8% that was highly variable (Bamford et al, 2007). Ambient noise during testing is an important contributor to higher false positive referral rates since screening is commonly conducted in less than ideal surroundings (Bamford et al, 2007). School environments are often noisy, and the equipment and expertise to take ambient noise measurements is unavailable (Academy, 2011). Even in cases where noise measurements are available, these may change from day to day and even from test to test due to the variability of noise sources. In an attempt to compensate for the effects of varying ambient noise levels, lower frequencies (,1000 Hz) are not included in recommended screening protocols (ASHA, 1997; Academy, 2011). A further factor influencing the success of preschool and school-entry hearing screening is poor follow-up compliance following a refer result. The recommendation for a child who is referred due to a failed hearing screening is diagnostic testing within 1 mo and no later than 3 mo after the initial screen (ASHA, 1997; Academy, 2011). Current evidence, however, indicates poor follow-up compliance from school-based hearing screening (Academy, 2011). In an evaluation of a large-scale metropolitan preschool hearing screening program, followup after referral was shown to be less than 20% (Flanary et al, 1999). Variable and high referral rates, alongside poor follow-up, poses a significant threat to the feasibility of preschool and school-based hearing screening programs. High referral rates causes families to incur unnecessary costs for follow-up and may undermine the integrity of the screening process. One way of addressing these concerns would be to include a diagnostic test immediately after the refer screen result. This may also ensure directed, more timely referrals
for audiological and/or medical treatment. The lack of compliant, sound-treated environments in typical school settings has traditionally, however, precluded the administration of diagnostic air- and bone-conduction audiometry in this setting. Referrals for diagnostic testing are consequently made at a later date to specific clinics. These appointments, however, have been shown to suffer from a high rate of follow-up default (Flanary et al, 1999; Bamford et al, 2007). The use of a new computer-operated, mobile audiometer has recently been validated and was found to accurately determine thresholds for elderly subjects within their natural environments, that is, retirement homes (Maclennan-Smith et al, 2013). This is achieved by incorporating insert earphones covered by circumaural earcups to allow for additional attenuation while employing external microphones that continuously monitor environmental noise (Swanepoel and Biagio, 2011; Maclennan-Smith et al, 2013). This portable and lightweight technology may likewise offer the flexibility to bring diagnostic audiometry into school environments without requiring a soundtreated facility. The current study investigated the validity of diagnostic air- and bone-conduction audiometry for children in a natural school environment using this technology. METHODS
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he institutional ethics committee of the University of Pretoria, South Africa, and that of the Western Cape Department of Education approved this repeatedmeasure, within-subject study before data collection commenced. In all cases children provided informed assent and parents provided informed consent prior to participation. Subjects A sample of 149 children (54% female) with an average age of 6.9 yr (SD 5 0.6; range 5 5–8) without significant hearing loss were recruited from two primary schools in the Western Cape, South Africa, for diagnostic pure-tone audiometry evaluations. The initial test was conducted at the school in a room provided by the school followed by the same evaluation at an audiology clinic in an audiometric booth. Subjects were included in the study when, at both evaluations, an intact tympanic membrane was otoscopically visible in combination with a normal, type A tympanogram. These criteria excluded from the study seven subjects with possible transitory middle ear pathology on the second visit. In cases of excessive cerumen, the audiologist removed this before testing if possible.
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Equipment Tympanometry was conducted as part of the screening procedure using an Interacoustics MT 10 handheld middle ear analyzer employing a 226 Hz probe tone. The audiometer used was a KUDUwave 5000 (GeoAxon, Pretoria, South Africa), a type 2 clinical audiometer (International Electrotechnical Commission [IEC], 2012) that was software controlled and operated via a notebook computer (Acer Travelmate 2492 running Windows XP). The audiometer hardware is encased in each circumaural earcup and powered by a USB cable plugged into the notebook. The transducers included embedded, custom insert earphones, which were covered by the circumaural cups after insertion. The insert earphone frequency response approximated that of the ER3A within 1 dB across test frequencies allowing for the use of the international insert earphone standard (International Organization for Standardization [ISO], 1994) for calibration. A B-71 bone oscillator (Kimmetrics, Smithsburg, MD) was placed on the forehead with a standard adjustable spring headband held in place on the center of the circumaural headband with a screw fitting (Fig. 1). The audiometer had two microphones on the circumaural earcup that monitored the environmental noise in octave bands during testing and was visually represented in real-time within the software (Fig. 2). The noise-monitoring function of the KUDUwave used low-pass (,125 Hz), seven single octave band-pass (125, 250, 500, 1000, 2000, 4000, and 8000 Hz), and high-pass (.8000 Hz) filters to separate the incoming
sound. The output of these filters was monitored in real-time and the peak value passed to the user interface software (eMOYO) every 100 msec. The filters had a stop-band attenuation of 90 dB and pass-band ripple of 0.003 dB. The environment-monitoring microphones incorporated in the headset were verified using an input signal of 1 kHz at 94 dB SPL to show a maximum variation of 3.6 dB across microphones. Calibration of the microphones was based on an effective attenuation level that was determined using expert subjects with normal hearing sensitivity. Pure tones were presented at irregular intervals to the test subjects at an intensity level 10 dB higher than the threshold of the test ear for frequencies in each octave band as well as the interoctave frequencies (125 to 8000 Hz). The insert earphones were placed in the ear canals with the 12 mm foam tip completely fitted into the canal and covered by the circumaural cups of the KUDUwave audiometer. Continuous narrowband noise was presented through freefield speakers situated at 45° 1 m in front of the subject. The intensity of the noise was slowly increased until the pure tones could not be detected. The average of these levels at each frequency and per ear was used as the effective attenuation level for each frequency. A response button was connected to the KUDUwave device to record patient responses to stimuli and to document response times. The audiometer was calibrated prior to commencement of the study using a type 1 sound level meter (Larson Davis System 824, Larson Davis, Provo, UT) with a G.R.A.S. (Holte, Denmark) IEC 711 coupler for insert earphones and an AMC493 Artificial Mastoid on an AEC101 coupler (Larson Davis) with 2559 1/2 inch microphone for the Radioear B-71 bone oscillator. Insert earphones were calibrated in accordance with ISO 389-2 and the bone oscillator according to ISO 389-3 (ISO, 1994). Testing in the audiometric booth was conducted using the same audiometer in a single-walled audiometric booth adhering to ambient noise levels specified by ANSI (2008) for evaluating hearing down to 0 dB HL from 250 to 8000 Hz. Procedures
Figure 1. Audiometer with insert earphones and circumaural earcups, which house the audiometer, and forehead bone conductor mounted centrally on headband.
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Subjects were tested twice (once in each test environment) with diagnostic air (250, 500, 1000, 2000, 3000, 4000, 6000, 8000 Hz) and bone-conduction (250, 500, 1000, 2000, 3000, 4000 Hz) pure-tone audiometry by the same experienced audiologist using the same audiometer. The test sequence was held constant, intentionally confining procedure variability for optimal comparison between the two test environments. In all cases, the initial test was conducted in a natural environment provided by the school, which constituted either a classroom, administrative room, or media room. Conducting the initial test in the natural environment limited traveling costs and inconvenience in the event
Diagnostic Pure-Tone Audiometry in Schools/Swanepoel et al
Figure 2. Screenshot of audiometer software demonstrating real-time monitoring of ambient noise levels while establishing thresholds.
that a subject proved not to meet the selection criteria. The second evaluation was conducted with the subject in a booth certified for unoccluded bone-conduction testing at an audiology clinic. Initial test results were not visible to the audiologist during the second evaluation, and they were not accessed prior to the test in the booth. The time interval between tests was an average of 9.3 (SD 5 68.4) days with the longest period being 46 days. An otoscopic examination and tympanometry were conducted prior to each evaluation to confirm the absence of any transient middle ear influences before inclusion in the study. Air-conduction pure tones were delivered via deeply inserted insert foam tips covered by the circumaural earcups of the audiometer for additional attenuation (insert earphone and circumaural earcup attenuation). In some cases, the 12 mm foam tips could not be fully inserted owing to the small size of the ear canal. In these cases the insert was placed as deeply as possible without causing undue discomfort. Berger et al (2003) reported average attenuation for deeply inserted insert foam plugs covered by circumaural earphones. This is similar to the current study’s double attenuation of 57, 62, 49, 40, 50, and 50 dB for 250, 500, 1000, 2000, 4000, and 8000 Hz, respectively. These attenuation values exceed those of typical transportable sound-treated booths
(Franks, 2001). Forehead placement bone-conduction audiometry was conducted with both ears occluded by the deep insertion of the earphones. Insert earphones were deeply inserted, in the majority of cases, with the foam tip completely into the canal to improve the attenuation of ambient noise (Berger, 1983; Berger and Killion, 1989; Berger et al, 2003) and to minimize the occlusion effect. Placing insert earphones down to the bony part of the ear canal reduces the occlusion effect allowing for bone-conduction evaluation with occluded ears (Dean and Martin, 2000; Stenfelt and Goode, 2005; Swanepoel and Biagio, 2011). Deep insertion required removal or partial removal of cerumen in at least one ear of 33.6% of subjects prior to their inclusion in the study. Verbal instructions were provided in English or Afrikaans to ensure that children understood the test procedures. Children were seen in groups of three or four. Each child was given an assent form depicting a preschool child being tested. The assent form was read to or with the group, and questions were answered. They were given the opportunity to draw a picture of themselves being tested and asked to sign the assent form if choosing to participate in the project. Subjects were conditioned in their groups using verbal instructions in English and/or Afrikaans together with demonstration of the desired response. The audiologist
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ensured that each child understood the test procedure and could respond consistently before commencing with the test. Subject responses with a patient response button allowed for recording reaction times for true positive responses within 1.5 sec after stimulus presentation. Thresholds were measured using a routine modified 10 dB descending and 5 dB ascending method (modified Hughson-Westlake method) commencing at 1000 Hz at 40 dB HL in the left ear and proceeding to the lower frequencies before recording thresholds at high frequencies. In the absence of a response at 40 dB HL, the intensity was increased in steps of 10 dB until a response was noted from where the bracketing method recommenced. A continuous contralateral effective masking level of 20 dB above the air-conduction threshold of the nontest ear was used for the forehead bone-conduction audiometry (ASHA, 2005). Average noise levels recorded (over a 30 min period) with a type 1 sound level meter in one of the schools showed average noise levels of 54.6 dBA (max 78.5 dBA; peak 95.4 dBA) in the test environment as opposed to 21.2 dBA in the sound-booth environment. The KUDUwave software actively monitored ambient noise levels across octave bands throughout the test procedures in both test environments. Whenever the noise exceeded the maximum ambient noise level allowed for establishing a threshold as indicated by the effective attenuation level in the KUDUwave software, the audiologist waited for the transient noise to abate or continued testing at other frequencies. Thresholds were evaluated down to a minimum of 0 dB HL Analysis The threshold data for air- and bone-conduction testing in the two environments were analyzed descriptively with average differences and absolute average differences presented with respective distributions. Correspondence of thresholds between the natural and clinical environments was described in
percentages and with 95% confidence intervals. A paired samples t-test with the significance level at 1% was used to determine whether hearing thresholds differed significantly between natural and clinical environments. RESULTS
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hreshold comparisons were made across air- and bone-conduction thresholds for left and right ears of 149 children between 5 and 8 yr of age. The overall average difference between the natural and booth environment thresholds was 0.0 dB (SD 5 3.6) for air conduction and 0.1 dB (SD 5 3.1) for bone conduction. Overall average absolute difference between the natural and booth environments was 2.1 dB (SD 5 2.9) for air-conduction and 1.6 dB (SD 5 2.7) for bone-conduction thresholds. Almost all of the air-conduction (96%) and bone-conduction (97%) threshold comparisons between the natural and booth environments were within 0 to 5 dB of each other. In both the natural and booth environment air-conduction thresholds were recorded down to 0 dB for almost half of the thresholds (47% and 48% respectively). Average air-conduction threshold differences between the natural environment and audiometric booth testing (Table 1) were between 20.2 and 0.5 dB with standard deviations between 2.5 and 4.7 dB across frequencies and ears. Average bone-conduction threshold differences between the natural environment and audiometric booth testing (Table 2) were between 20.2 and 0.6 dB with standard deviations of between 2.6 and 4.0 dB across frequencies and ears. The absolute differences between the thresholds are combined for left and right ears in Table 3 and illustrated across ears in Figures 3 and 4. Differences in the natural and audiometric booth environments across ears and frequencies were within 65 dB for 96% of air-conduction thresholds (n 5 2374) and 97% of bone-conduction thresholds (n 5 1755).
Table 1. Differences in Air-Conduction Thresholds Recorded in the Natural and Audiometric Booth Environments Freq (Hz)
250
500
n Avg SD 95% CI 65 dB %
149 0.0 3.7 20.6;0.6 97
149 0.5 4.1 20.1;1.2 95
n Avg SD 95% CI 65 dB %
148 20.1 4.7 20.9;0.6 89
148 0.2 4.2 20.5;0.8 93
1000
2000
3000
Left AC Difference (Natural and Booth) 149 149 149 0.3 20.2 20.2 3.7 3.6 2.9 20.3;0.9 20.7;0.4 20.7;0.2 96 97 99 Right AC Difference (Natural and Booth) 148 147 148 20.5 20.1 0.2 4.0 3.5 3.4 21.1;0.2 20.6;0.5 20.3;0.8 95 97 98
4000
6000
8000
149 0.1 2.7 20.4;0.5 98
149 0.2 3.0 20.3;0.7 96
149 0.3 4.2 0.3;1.0 93
148 0.0 2.8 20.4;0.5 98
148 0.1 2.5 20.3;0.5 98
147 20.2 3.9 20.9;0.4 93
Note: Thresholds recorded in the booth subtracted from those recorded in the natural environment.
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Table 2. Differences in Bone-Conduction Thresholds Recorded in the Natural and Audiometric Booth Environments Freq (Hz)
250
n Avg SD 95% CI 65 dB %
145 20.1 2.6 20.5;0.3 99
N Avg SD 95% CI 65 dB %
146 0.5 2.8 0.1;1.0 97
500
1000
2000
Left BC Difference (Natural and Booth) 146 146 146 0.6 0.5 0.0 2.8 4.0 3.5 0.1;1.0 201;1.2 20.5;0.6 96 92 97 Right BC Difference (Natural and Booth) 148 148 148 0.0 0.0 0.0 2.6 3.2 3.7 20.4;0.4 20.5;0.5 20.6;0.6 99 97 97
3000
4000
145 20.1 2.8 20.6;0.3 99
143 0.1 2.7 20.3;0.6 97
147 0.1 3.4 20.5;0.6 97
147 20.2 2.6 20.6;0.3 97
Note: Thresholds recorded in the booth subtracted from those recorded in the natural environment.
Since subjects were young school children without any significant hearing impairment and testing was conducted down to 0 dB HL, a floor-effect could have influenced results. To evaluate results without this possible influence, a comparison between thresholds (natural vs. booth) was done excluding any comparisons for thresholds of 0 dB HL in either environment (Table 4). Excluding the possibility of the floor-effect, average air-conduction threshold differences between the natural and audiometric booth environment (Table 4) were between 20.2 and 0.6 (SDs 5 2.9–3.9 dB), and average bone-conduction threshold differences were between 20.7 and 0.3 dB (SDs 5 1.9–3.7 dB). The overall average absolute difference was 2.7 (SD 5 3.0) and 3.0 (SD 5 2.8) for air- and bone-conduction comparisons respectively. There were no statistically significant differences between thresholds recorded in the natural and booth environments for air- and bone-conduction audiometry (paired-samples t-test; p . 0.01). Number of responses to pure-tone presentations and average reaction time and the standard deviation of these were also compared between the natural and audiometric booth environments within subjects and showed no significant difference (paired samples t-test; p . 0.01). DISCUSSION
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iagnostic audiometry in a school environment without a sound-treated booth will require sufficient attenuation and monitoring of ambient noise to ensure the accurate recording of hearing thresholds (Swanepoel, Clark, et al, 2010; Swanepoel, Olusanya, et al, 2010; Maclennan-Smith et al, 2013). In the current study, a recently validated computer-operated audiometer employing passive attenuation using insert earphones covered by circumaural earcups coupled with real-time monitoring of environmental noise was evaluated for air- and bone-conduction threshold measurement in
a natural environment. Double transducer attenuation using insert foam plugs and circumaural earcups produce a significant increase in ambient noise attenuation that may actually exceed typical attenuation for transportable sound booths (Franks, 2001; Berger et al, 2003). Results of the current study confirmed statistically and clinically equivalent hearing thresholds for children tested in a school environment compared to a sound-treated booth. Air-conduction thresholds measured in the natural environment and subsequently in a standard audiometric booth corresponded within typical 5 dB or less testretest limits for thresholds measured in a sound booth (Stuart et al, 1991; Smith-Olinde et al, 2006; Margolis et al, 2010; Swanepoel, Mngemane, et al, 2010; Swanepoel and Biagio, 2011). Average absolute air-conduction threshold differences for the current study (2.1 6 2.9 dB) were within previously reported test-retest absolute average difference values (3.6 6 3.9 dB and 3.5 6 3.8 dB) for the same audiometer (Swanepoel, Mngemane, et al, 2010; Swanepoel and Biagio, 2011). These are also similar to recently reported threshold differences for elderly persons (2.7 6 3.1 dB), using the same audiometer, in Table 3. Absolute Differences in Air- and BoneConduction Thresholds Recorded in the Natural and Audiometric Booth Environments (left and right ears combined) Freq (Hz)
250 500 1000 2000 3000 4000 6000 8000
AC Threshold Correspondence Avg (Abs) 2.7 2.8 2.5 2.2 SD 3.2 3.1 2.9 2.8 n 297 297 297 296 65 dB % 93 94 96 97 BC Threshold Correspondence Avg (Abs) 1.2 1.2 2.1 2.3 SD 2.4 2.5 3.0 2.8 n 291 294 294 294 65 dB % 98 97 94 97
(Natural and 1.8 1.3 2.6 2.4 297 297 98 98 (Natural and 1.6 1.1 2.6 2.4 292 290 98 97
Booth) 1.3 2.3 2.5 3.3 297 296 97 93 Booth)
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Figure 3. Average absolute difference between air-conduction thresholds recorded in the natural and audiometric booth environments (error bars 5 1 SD)
retirement home facilities compared to an audiometric sound booth (Maclennan-Smith et al, 2013). In the current study 96% of threshold comparisons were within 5 dB or better, which is similar to the correspondence (95%) of thresholds recorded using the same audiometer for elderly persons in retirement homes compared to an audiometric sound booth (Maclennan-Smith et al, 2013). This compares favorably to the 88% test-retest correspondence within 5 dB or less reported previously for this audiometer (Swanepoel, Mngemane, et al, 2010). The slightly better correspondence between air-conduction thresholds recorded in the natural and sound booth environments compared with the test-retest differences reported by Swanepoel, Mngemane, et al (2010) may partly be attributed to the omission of 125 Hz as a test frequency in the current study. This low frequency showed a larger test-retest discrepancy than the other frequencies in the Swanepoel, Mngemane, et al (2010) study. The average absolute difference in bone-conduction thresholds recorded in the natural environment and audiometric booth (1.6 62.7 SD) was less than previously reported bone-conduction test-retest differences (Laukli and Fjermedal, 1990; Margolis et al, 2010;
Figure 4. Average absolute difference between bone-conduction thresholds recorded in the natural and audiometric booth environments (error bars 5 1 SD)
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Swanepoel and Biagio, 2011). Reported absolute differences for bone-conduction thresholds in elderly persons (3.4 6 4.3 dB), determined using the same audiometer in retirement facilities compared to an audiometric sound booth, were within typical test-retest differences but slightly larger than the current study differences (Maclennan-Smith et al, 2013). In the current study 97% of bone-conduction thresholds corresponded within 5 dB or less compared to 86% of threshold comparisons between the natural and booth environments recorded for the elderly population (Maclennan-Smith et al, 2013). Improved bone-conduction threshold correspondence in the current study is most likely due, in part, to a floor-effect related to the majority (82%; 316/1755) of thresholds for these children recorded down to 0 dB HL. To assess air- and bone-conduction threshold correspondence without the influence of a possible flooreffect, a comparison was made between thresholds excluding all thresholds recorded at 0 dB in either the natural or booth environments (Table 4). The overall average absolute air-conduction threshold difference (2.1 6 2.9 dB) was similar to the difference when excluding the floor-effect (2.7 6 3.0 dB). The overall absolute bone-conduction threshold difference between environments (1.6 6 2.7 dB) increased when the floor-effect was excluded (3.0 6 2.8 dB). In the bone-conduction results the influence of a floor-effect was confirmed. Correspondence of thresholds between conditions, excluding the floor-effect, was, however, still well within typical test-retest differences previously reported for boneconduction (Laukli and Fjermedal, 1990; Margolis et al, 2010; Swanepoel and Biagio, 2011). Findings from the current study provide evidence that valid diagnostic air- and bone-conduction puretone hearing thresholds can be recorded using a mobile audiometer without a sound booth in school environments. Using insert earphone and circumaural earcup attenuation provides passive control of environmental noise while continuous monitoring of ambient noise provides real-time feedback on extraneous interference. Active noise measurements provide a measure of quality control to monitor noise levels according to the average attenuation provided by the test setup in a typical group of subjects. By employing these attenuation levels, the software can be programmed to monitor ambient noise levels across octave or interoctave levels, according to standards for audiometric test environments (e.g., ANSI, 2008). This type of technology opens up the possibility of mobile diagnostic testing for children immediately after they refer a preschool or school-based hearing screening. This may have a significant impact on the time lost due to referral visits (recommended to be within 3 mo) and could address the typical caveat of preschool and school-based screen follow-up defaults (Flanary et al, 1999; Bamford et al, 2007; Academy, 2011). Directed
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Table 4. Differences in Air- and Bone-Conduction Threshold Comparisons between the Natural and Audiometric Booth Environments for Thresholds >0 dB in Either Condition Freq (Hz)
250
n Avg SD 65 dB %
219 20.2 3.4 99
n Avg SD 65 dB %
7 20.7 1.9 100
500
1000
2000
3000
4000
6000
8000
35 0.1 3.5 97
80 0.6 3.9 98
AC Threshold Differences (Natural and Booth) for Thresholds .0 dB 200 161 130 103 45 0.4 0.2 0.1 20.1 0.6 3.3 2.9 2.8 3.0 2.9 99 99 100 98 98 BC Threshold Differences (Natural and Booth) for Thresholds .0 dB 25 61 109 84 30 20.2 0.1 0.3 20.2 0.2 3.7 3.0 3.0 3.0 2.5 92 100 100 98 97
Note: Thresholds recorded in the booth subtracted from those recorded in the natural environment.
referrals based on diagnostic audiometry could be made for audiological and/or medical intervention without delay. In developing countries where school-based screening may be the first hearing screening children receive, the ability to conduct diagnostic assessments onsite would be invaluable especially when considering the general dearth of audiological equipment and sound booths in these underserved regions (Swanepoel, Clark, et al, 2010; Swanepoel, Olusanya, et al, 2010). In some cases, should valid diagnostic audiometry be completed for children at school and medical conditions ruled out, it may be possible for audiological intervention to be initiated on-site. A cautionary consideration when using this technology is the possible influence of the occlusion effect of the nontest ear when bone-conduction testing outside an audiometric booth is conducted. Deeply inserted insert earphones can minimize the occlusion effect (250–1000 Hz) to a level that is considered to be clinically insignificant (Stenfelt and Goode, 2005), but achieving deep insertion of the insert earphone in young school children may be challenging in certain cases where ear canals are particularly small or in the presence of excessive cerumen or foreign bodies. In these cases, correction values may be necessary to compensate for the occlusion effect (Dean and Martin, 2000). Alternatively, circumaural earphones may be used to avoid the occlusion effect. CONCLUSION
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he ability to follow-up referrals for hearing screening with valid on-site diagnostic testing may improve the efficacy of current preschool and schoolbased screening programs. Current study findings demonstrate the possibility of determining accurate air- and bone-conduction thresholds using passive attenuation with insert earphones covered by circumaural earcups alongside real-time monitoring of environmental noise through external microphones. The immediate availability of diagnostic pure-tone audiometry following a
school screening referral would ensure that prompt directed referrals for audiological and/or medical intervention could be made. REFERENCES American Academy of Audiology (Academy). (2011) Childhood Hearing Screening. American Academy of Audiology Clinical Practice Guidelines. www.audiology.org/resources/documentlibrary/ Documents/ChildhoodScreeningGuidelines.pdf. American Academy of Pediatrics, Joint Committee on Infant Hearing (JCIH). (2007) Year 2007 position statement: principles and guidelines for early hearing detection and intervention programs. Pediatrics 120(4):898–921. American National Standards Institute (ANSI). (2008) Maximum Permissible Ambient Noise Levels for Audiometric Test Rooms. ANSI S3.1-1999 (R2008). New York: American National Standards Institute. American Speech-Language-Hearing Association (ASHA). (1997) Guidelines for Audiological Screening. Rockville, MD: American Speech-Language-Hearing Association. American Speech-Language-Hearing Association (ASHA). (2005) Guidelines for Manual Pure-Tone Threshold Audiometry www. asha.org/policy. Bamford J, Fortnum H, Bristow K, et al. (2007) Current practice, accuracy, effectiveness and cost-effectiveness of the school entry hearing screen. Health Technol Assess 11(32):1–168, iii–iv. Berger EH. (1983) Laboratory attenuation of earmuffs and earplugs both singly and in combination. Am Ind Hyg Assoc J 44: 321–329. Berger EH, Kieper RW, Gauger D. (2003) Hearing protection: surpassing the limits to attenuation imposed by the bone-conduction pathways. J Acoust Soc Am 114(4, Pt. 1):1955–1967. Berger EH, Killion MC. (1989) Comparison of the noise attenuation of three audiometric earphones, with additional data on masking near threshold. J Acoust Soc Am 86:1392–1403. Dean MS, Martin FN. (2000) Insert earphone depth and the occlusion effect. Am J Audiol 9(2):131–134. Flanary VA, Flanary CJ, Colombo J, Kloss D. (1999) Mass hearing screening in kindergarten students. Int J Pediatr Otorhinolaryngol 50(2):93–98.
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Fortnum H, Summerfield A, Marshall D, Davis A, Bamford J, Yoshinaga-Itano C, Hind S. (2001) Prevalence of permanent childhood hearing impairment in the United Kingdom and implications for universal neonatal hearing screening: questionnaire based ascertainment study. Br Med J 323(7312):536–542. Franks JR. (2001) Hearing measurement. In: Goelzer B, Hansen C, Sehrndt G, eds. Occupational Exposure to Noise: Evaluation, Prevention and Control. Geneva: World Health Organization, 183–232. International Electrotechnical Commission (IEC). (2012) Electroacoustics—Audiometric Equipment—Part 1: Equipment for Pure-Tone Audiometry. Part 2: Equipment for Speech Audiometry. IEC 60645-1/2:2012. International Organization for Standardization (ISO). (1994) Acoustics—Reference Zero for the Calibration of Audiometric Equipment—Part 2: Reference Equivalent Threshold Sound Pressure Levels for Pure Tones and Insert Earphones. ISO 389-2:1994. Laukli E, Fjermedal O. (1990) Reproducibility of hearing threshold measurements. Supplementary data on bone-conduction and speech audiometry. Scand Audiol 19(3):187–190.
Olusanya B, Swanepoel W, Chapchap M, et al. (2007) Progress towards early detection services for infants with hearing loss in developing countries. BMC Health Serv Res 7:14. Smith-Olinde L, Nicholson N, Chivers C, Highley P, Williams DK. (2006) Test-retest reliability of in situ unaided thresholds in adults. Am J Audiol 15(1):75–80. Stenfelt S, Goode RL. (2005) Bone-conducted sound: physiological and clinical aspects. Otol Neurotol 26(6):1245–1261. Stuart A, Stenstrom R, Tompkins C, Vandenhoff S. (1991) Test-retest variability in audiometric threshold with supraaural and insert earphones among children and adults. Audiology 30(2):82–90. Swanepoel W, Clark JL, Koekemoer D, et al. (2010) Telehealth in audiology: the need and potential to reach underserved communities. Int J Audiol 49(3):195–202. Swanepoel W, Olusanya BO, Mars M. (2010) Hearing health-care delivery in sub-Saharan Africa—a role for tele-audiology. J Telemed Telecare 16(2):53–56.
Maclennan-Smith F, Swanepoel W, Hall JW, 3rd. (2013) Validity of diagnostic pure-tone audiometry without a sound-treated environment in older adults. Int J Audiol 52(2):66–73.
Swanepoel W, Mngemane S, Molemong S, Mkwanazi H, Tutshini S. (2010) Hearing assessment-reliability, accuracy, and efficiency of automated audiometry. Telemed J E Health 16(5):557–563.
Margolis RH, Glasberg BR, Creeke S, Moore BCJ. (2010) AMTAS: automated method for testing auditory sensitivity: validation studies. Int J Audiol 49(3):185–194.
Swanepoel W, Biagio L. (2011) Validity of diagnostic computerbased air and forehead bone conduction audiometry. J Occup Environ Hyg 8(4):210–214.
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Diagnostic Pure-Tone Audiometry in Schools: Mobile Testing without a Sound-Treated Environment DOI: 10.3766/jaaa.24.10.10 De Wet Swanepoel*†‡ Felicity Maclennan-Smith* James W. Hall*
Abstract Purpose: To validate diagnostic pure-tone audiometry in schools without a sound-treated environment using an audiometer that incorporates insert earphones covered by circumaural earcups and real-time environmental noise monitoring. Research Design: A within-subject repeated measures design was employed to compare air (250 to 8000 Hz) and bone (250 to 4000 Hz) conduction pure-tone thresholds measured in natural school environments with thresholds measured in a sound-treated booth. Study Sample: 149 children (54% female) with an average age of 6.9 yr (SD 5 0.6; range 5 5–8). Results: Average difference between the booth and natural environment thresholds was 0.0 dB (SD 5 3.6) for air conduction and 0.1 dB (SD 5 3.1) for bone conduction. Average absolute difference between the booth and natural environment was 2.1 dB (SD 5 2.9) for air conduction and 1.6 dB (SD 5 2.7) for bone conduction. Almost all air- (96%) and bone-conduction (97%) threshold comparisons between the natural and booth test environments were within 0 to 5 dB. No statistically significant differences between thresholds recorded in the natural and booth environments for air- and bone-conduction audiometry were found ( p . 0.01). Conclusions: Diagnostic air- and bone-conduction audiometry in schools, without a sound-treated room, is possible with sufficient earphone attenuation and real-time monitoring of environmental noise. Audiological diagnosis on-site for school screening may address concerns of false-positive referrals and poor follow-up compliance and allow for direct referral to audiological and/or medical intervention. Key Words: Air conduction, bone conduction, diagnostic audiometry, hearing screening, school-entry screening Abbreviation: NHS 5 newborn hearing screening
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evelopmental and socioeconomic benefits of early detection of hearing loss, primarily through newborn hearing screening (NHS) programs, are now widely established and accepted (American Academy of Pediatrics, Joint Committee on Infant Hearing [JCIH], 2007). Despite the success of NHS programs, a significant number of permanent moderate or greater bilateral and unilateral impairments are only identified around the time of school entry (Bamford et al, 2007; American Academy of Audiology [Academy], 2011). This is attributed to several reasons including (1) NHS screen technologies targeting hearing loss of 30 to 40 dB omitting screening
for low-frequency hearing loss; (2) not all infants referred from NHS receive diagnostic services; and (3) the occurrence of late-onset, acquired, or progressive losses (Bamford et al, 2007; Academy, 2011). In developing countries where NHS programs are scarce, school-based screening may also be the first opportunity to identify hearing loss (Olusanya et al, 2007). According to Fortnum and colleagues (2001), for every 10 children identified with permanent bilateral hearing loss greater than 40 dB through NHS, an additional five to nine children will present with similar hearing loss by the age of 9 yr.
*Department of Communication Pathology, University of Pretoria, South Africa; †Ear Sciences Centre, School of Surgery, University of Western Australia, Nedlands, Australia; ‡Ear Science Institute Australia, Subiaco, Australia De Wet Swanepoel, Ph.D., Department of Communication Pathology, University of Pretoria, C/o Lynnwood and University Roads, Hatfield, 0002, South Africa; E-mail: [email protected]
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Based on current evidence, the American Academy of Audiology (2011) has recommended preschool and schoolbased hearing screening for permanent hearing loss and longstanding and frequently recurring conductive hearing loss, which may impact linguistic development and school performance. This is proposed as a critical strategy toward optimal academic outcomes for children with possible long-term economic savings. The recommended approach for school-based screening has remained pure-tone audiometry as first-stage screen (American Speech-Language-Hearing Association [ASHA], 1997; Bamford et al, 2007; Academy, 2011). While tympanometry screening may target screening for middle ear disorders, like otitis media with effusion, it is usually recommended as a second-stage screen after a puretone audiometry refer result (ASHA, 1997; Academy, 2011; Bamford et al, 2007). One of the most significant and persistent problems faced by school-based screening programs are high referral rates. A summary of UK-based school-entry screening indicated a median referral rate of 8% that was highly variable (Bamford et al, 2007). Ambient noise during testing is an important contributor to higher false positive referral rates since screening is commonly conducted in less than ideal surroundings (Bamford et al, 2007). School environments are often noisy, and the equipment and expertise to take ambient noise measurements is unavailable (Academy, 2011). Even in cases where noise measurements are available, these may change from day to day and even from test to test due to the variability of noise sources. In an attempt to compensate for the effects of varying ambient noise levels, lower frequencies (,1000 Hz) are not included in recommended screening protocols (ASHA, 1997; Academy, 2011). A further factor influencing the success of preschool and school-entry hearing screening is poor follow-up compliance following a refer result. The recommendation for a child who is referred due to a failed hearing screening is diagnostic testing within 1 mo and no later than 3 mo after the initial screen (ASHA, 1997; Academy, 2011). Current evidence, however, indicates poor follow-up compliance from school-based hearing screening (Academy, 2011). In an evaluation of a large-scale metropolitan preschool hearing screening program, followup after referral was shown to be less than 20% (Flanary et al, 1999). Variable and high referral rates, alongside poor follow-up, poses a significant threat to the feasibility of preschool and school-based hearing screening programs. High referral rates causes families to incur unnecessary costs for follow-up and may undermine the integrity of the screening process. One way of addressing these concerns would be to include a diagnostic test immediately after the refer screen result. This may also ensure directed, more timely referrals
for audiological and/or medical treatment. The lack of compliant, sound-treated environments in typical school settings has traditionally, however, precluded the administration of diagnostic air- and bone-conduction audiometry in this setting. Referrals for diagnostic testing are consequently made at a later date to specific clinics. These appointments, however, have been shown to suffer from a high rate of follow-up default (Flanary et al, 1999; Bamford et al, 2007). The use of a new computer-operated, mobile audiometer has recently been validated and was found to accurately determine thresholds for elderly subjects within their natural environments, that is, retirement homes (Maclennan-Smith et al, 2013). This is achieved by incorporating insert earphones covered by circumaural earcups to allow for additional attenuation while employing external microphones that continuously monitor environmental noise (Swanepoel and Biagio, 2011; Maclennan-Smith et al, 2013). This portable and lightweight technology may likewise offer the flexibility to bring diagnostic audiometry into school environments without requiring a soundtreated facility. The current study investigated the validity of diagnostic air- and bone-conduction audiometry for children in a natural school environment using this technology. METHODS
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he institutional ethics committee of the University of Pretoria, South Africa, and that of the Western Cape Department of Education approved this repeatedmeasure, within-subject study before data collection commenced. In all cases children provided informed assent and parents provided informed consent prior to participation. Subjects A sample of 149 children (54% female) with an average age of 6.9 yr (SD 5 0.6; range 5 5–8) without significant hearing loss were recruited from two primary schools in the Western Cape, South Africa, for diagnostic pure-tone audiometry evaluations. The initial test was conducted at the school in a room provided by the school followed by the same evaluation at an audiology clinic in an audiometric booth. Subjects were included in the study when, at both evaluations, an intact tympanic membrane was otoscopically visible in combination with a normal, type A tympanogram. These criteria excluded from the study seven subjects with possible transitory middle ear pathology on the second visit. In cases of excessive cerumen, the audiologist removed this before testing if possible.
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Equipment Tympanometry was conducted as part of the screening procedure using an Interacoustics MT 10 handheld middle ear analyzer employing a 226 Hz probe tone. The audiometer used was a KUDUwave 5000 (GeoAxon, Pretoria, South Africa), a type 2 clinical audiometer (International Electrotechnical Commission [IEC], 2012) that was software controlled and operated via a notebook computer (Acer Travelmate 2492 running Windows XP). The audiometer hardware is encased in each circumaural earcup and powered by a USB cable plugged into the notebook. The transducers included embedded, custom insert earphones, which were covered by the circumaural cups after insertion. The insert earphone frequency response approximated that of the ER3A within 1 dB across test frequencies allowing for the use of the international insert earphone standard (International Organization for Standardization [ISO], 1994) for calibration. A B-71 bone oscillator (Kimmetrics, Smithsburg, MD) was placed on the forehead with a standard adjustable spring headband held in place on the center of the circumaural headband with a screw fitting (Fig. 1). The audiometer had two microphones on the circumaural earcup that monitored the environmental noise in octave bands during testing and was visually represented in real-time within the software (Fig. 2). The noise-monitoring function of the KUDUwave used low-pass (,125 Hz), seven single octave band-pass (125, 250, 500, 1000, 2000, 4000, and 8000 Hz), and high-pass (.8000 Hz) filters to separate the incoming
sound. The output of these filters was monitored in real-time and the peak value passed to the user interface software (eMOYO) every 100 msec. The filters had a stop-band attenuation of 90 dB and pass-band ripple of 0.003 dB. The environment-monitoring microphones incorporated in the headset were verified using an input signal of 1 kHz at 94 dB SPL to show a maximum variation of 3.6 dB across microphones. Calibration of the microphones was based on an effective attenuation level that was determined using expert subjects with normal hearing sensitivity. Pure tones were presented at irregular intervals to the test subjects at an intensity level 10 dB higher than the threshold of the test ear for frequencies in each octave band as well as the interoctave frequencies (125 to 8000 Hz). The insert earphones were placed in the ear canals with the 12 mm foam tip completely fitted into the canal and covered by the circumaural cups of the KUDUwave audiometer. Continuous narrowband noise was presented through freefield speakers situated at 45° 1 m in front of the subject. The intensity of the noise was slowly increased until the pure tones could not be detected. The average of these levels at each frequency and per ear was used as the effective attenuation level for each frequency. A response button was connected to the KUDUwave device to record patient responses to stimuli and to document response times. The audiometer was calibrated prior to commencement of the study using a type 1 sound level meter (Larson Davis System 824, Larson Davis, Provo, UT) with a G.R.A.S. (Holte, Denmark) IEC 711 coupler for insert earphones and an AMC493 Artificial Mastoid on an AEC101 coupler (Larson Davis) with 2559 1/2 inch microphone for the Radioear B-71 bone oscillator. Insert earphones were calibrated in accordance with ISO 389-2 and the bone oscillator according to ISO 389-3 (ISO, 1994). Testing in the audiometric booth was conducted using the same audiometer in a single-walled audiometric booth adhering to ambient noise levels specified by ANSI (2008) for evaluating hearing down to 0 dB HL from 250 to 8000 Hz. Procedures
Figure 1. Audiometer with insert earphones and circumaural earcups, which house the audiometer, and forehead bone conductor mounted centrally on headband.
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Subjects were tested twice (once in each test environment) with diagnostic air (250, 500, 1000, 2000, 3000, 4000, 6000, 8000 Hz) and bone-conduction (250, 500, 1000, 2000, 3000, 4000 Hz) pure-tone audiometry by the same experienced audiologist using the same audiometer. The test sequence was held constant, intentionally confining procedure variability for optimal comparison between the two test environments. In all cases, the initial test was conducted in a natural environment provided by the school, which constituted either a classroom, administrative room, or media room. Conducting the initial test in the natural environment limited traveling costs and inconvenience in the event
Diagnostic Pure-Tone Audiometry in Schools/Swanepoel et al
Figure 2. Screenshot of audiometer software demonstrating real-time monitoring of ambient noise levels while establishing thresholds.
that a subject proved not to meet the selection criteria. The second evaluation was conducted with the subject in a booth certified for unoccluded bone-conduction testing at an audiology clinic. Initial test results were not visible to the audiologist during the second evaluation, and they were not accessed prior to the test in the booth. The time interval between tests was an average of 9.3 (SD 5 68.4) days with the longest period being 46 days. An otoscopic examination and tympanometry were conducted prior to each evaluation to confirm the absence of any transient middle ear influences before inclusion in the study. Air-conduction pure tones were delivered via deeply inserted insert foam tips covered by the circumaural earcups of the audiometer for additional attenuation (insert earphone and circumaural earcup attenuation). In some cases, the 12 mm foam tips could not be fully inserted owing to the small size of the ear canal. In these cases the insert was placed as deeply as possible without causing undue discomfort. Berger et al (2003) reported average attenuation for deeply inserted insert foam plugs covered by circumaural earphones. This is similar to the current study’s double attenuation of 57, 62, 49, 40, 50, and 50 dB for 250, 500, 1000, 2000, 4000, and 8000 Hz, respectively. These attenuation values exceed those of typical transportable sound-treated booths
(Franks, 2001). Forehead placement bone-conduction audiometry was conducted with both ears occluded by the deep insertion of the earphones. Insert earphones were deeply inserted, in the majority of cases, with the foam tip completely into the canal to improve the attenuation of ambient noise (Berger, 1983; Berger and Killion, 1989; Berger et al, 2003) and to minimize the occlusion effect. Placing insert earphones down to the bony part of the ear canal reduces the occlusion effect allowing for bone-conduction evaluation with occluded ears (Dean and Martin, 2000; Stenfelt and Goode, 2005; Swanepoel and Biagio, 2011). Deep insertion required removal or partial removal of cerumen in at least one ear of 33.6% of subjects prior to their inclusion in the study. Verbal instructions were provided in English or Afrikaans to ensure that children understood the test procedures. Children were seen in groups of three or four. Each child was given an assent form depicting a preschool child being tested. The assent form was read to or with the group, and questions were answered. They were given the opportunity to draw a picture of themselves being tested and asked to sign the assent form if choosing to participate in the project. Subjects were conditioned in their groups using verbal instructions in English and/or Afrikaans together with demonstration of the desired response. The audiologist
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ensured that each child understood the test procedure and could respond consistently before commencing with the test. Subject responses with a patient response button allowed for recording reaction times for true positive responses within 1.5 sec after stimulus presentation. Thresholds were measured using a routine modified 10 dB descending and 5 dB ascending method (modified Hughson-Westlake method) commencing at 1000 Hz at 40 dB HL in the left ear and proceeding to the lower frequencies before recording thresholds at high frequencies. In the absence of a response at 40 dB HL, the intensity was increased in steps of 10 dB until a response was noted from where the bracketing method recommenced. A continuous contralateral effective masking level of 20 dB above the air-conduction threshold of the nontest ear was used for the forehead bone-conduction audiometry (ASHA, 2005). Average noise levels recorded (over a 30 min period) with a type 1 sound level meter in one of the schools showed average noise levels of 54.6 dBA (max 78.5 dBA; peak 95.4 dBA) in the test environment as opposed to 21.2 dBA in the sound-booth environment. The KUDUwave software actively monitored ambient noise levels across octave bands throughout the test procedures in both test environments. Whenever the noise exceeded the maximum ambient noise level allowed for establishing a threshold as indicated by the effective attenuation level in the KUDUwave software, the audiologist waited for the transient noise to abate or continued testing at other frequencies. Thresholds were evaluated down to a minimum of 0 dB HL Analysis The threshold data for air- and bone-conduction testing in the two environments were analyzed descriptively with average differences and absolute average differences presented with respective distributions. Correspondence of thresholds between the natural and clinical environments was described in
percentages and with 95% confidence intervals. A paired samples t-test with the significance level at 1% was used to determine whether hearing thresholds differed significantly between natural and clinical environments. RESULTS
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hreshold comparisons were made across air- and bone-conduction thresholds for left and right ears of 149 children between 5 and 8 yr of age. The overall average difference between the natural and booth environment thresholds was 0.0 dB (SD 5 3.6) for air conduction and 0.1 dB (SD 5 3.1) for bone conduction. Overall average absolute difference between the natural and booth environments was 2.1 dB (SD 5 2.9) for air-conduction and 1.6 dB (SD 5 2.7) for bone-conduction thresholds. Almost all of the air-conduction (96%) and bone-conduction (97%) threshold comparisons between the natural and booth environments were within 0 to 5 dB of each other. In both the natural and booth environment air-conduction thresholds were recorded down to 0 dB for almost half of the thresholds (47% and 48% respectively). Average air-conduction threshold differences between the natural environment and audiometric booth testing (Table 1) were between 20.2 and 0.5 dB with standard deviations between 2.5 and 4.7 dB across frequencies and ears. Average bone-conduction threshold differences between the natural environment and audiometric booth testing (Table 2) were between 20.2 and 0.6 dB with standard deviations of between 2.6 and 4.0 dB across frequencies and ears. The absolute differences between the thresholds are combined for left and right ears in Table 3 and illustrated across ears in Figures 3 and 4. Differences in the natural and audiometric booth environments across ears and frequencies were within 65 dB for 96% of air-conduction thresholds (n 5 2374) and 97% of bone-conduction thresholds (n 5 1755).
Table 1. Differences in Air-Conduction Thresholds Recorded in the Natural and Audiometric Booth Environments Freq (Hz)
250
500
n Avg SD 95% CI 65 dB %
149 0.0 3.7 20.6;0.6 97
149 0.5 4.1 20.1;1.2 95
n Avg SD 95% CI 65 dB %
148 20.1 4.7 20.9;0.6 89
148 0.2 4.2 20.5;0.8 93
1000
2000
3000
Left AC Difference (Natural and Booth) 149 149 149 0.3 20.2 20.2 3.7 3.6 2.9 20.3;0.9 20.7;0.4 20.7;0.2 96 97 99 Right AC Difference (Natural and Booth) 148 147 148 20.5 20.1 0.2 4.0 3.5 3.4 21.1;0.2 20.6;0.5 20.3;0.8 95 97 98
4000
6000
8000
149 0.1 2.7 20.4;0.5 98
149 0.2 3.0 20.3;0.7 96
149 0.3 4.2 0.3;1.0 93
148 0.0 2.8 20.4;0.5 98
148 0.1 2.5 20.3;0.5 98
147 20.2 3.9 20.9;0.4 93
Note: Thresholds recorded in the booth subtracted from those recorded in the natural environment.
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Table 2. Differences in Bone-Conduction Thresholds Recorded in the Natural and Audiometric Booth Environments Freq (Hz)
250
n Avg SD 95% CI 65 dB %
145 20.1 2.6 20.5;0.3 99
N Avg SD 95% CI 65 dB %
146 0.5 2.8 0.1;1.0 97
500
1000
2000
Left BC Difference (Natural and Booth) 146 146 146 0.6 0.5 0.0 2.8 4.0 3.5 0.1;1.0 201;1.2 20.5;0.6 96 92 97 Right BC Difference (Natural and Booth) 148 148 148 0.0 0.0 0.0 2.6 3.2 3.7 20.4;0.4 20.5;0.5 20.6;0.6 99 97 97
3000
4000
145 20.1 2.8 20.6;0.3 99
143 0.1 2.7 20.3;0.6 97
147 0.1 3.4 20.5;0.6 97
147 20.2 2.6 20.6;0.3 97
Note: Thresholds recorded in the booth subtracted from those recorded in the natural environment.
Since subjects were young school children without any significant hearing impairment and testing was conducted down to 0 dB HL, a floor-effect could have influenced results. To evaluate results without this possible influence, a comparison between thresholds (natural vs. booth) was done excluding any comparisons for thresholds of 0 dB HL in either environment (Table 4). Excluding the possibility of the floor-effect, average air-conduction threshold differences between the natural and audiometric booth environment (Table 4) were between 20.2 and 0.6 (SDs 5 2.9–3.9 dB), and average bone-conduction threshold differences were between 20.7 and 0.3 dB (SDs 5 1.9–3.7 dB). The overall average absolute difference was 2.7 (SD 5 3.0) and 3.0 (SD 5 2.8) for air- and bone-conduction comparisons respectively. There were no statistically significant differences between thresholds recorded in the natural and booth environments for air- and bone-conduction audiometry (paired-samples t-test; p . 0.01). Number of responses to pure-tone presentations and average reaction time and the standard deviation of these were also compared between the natural and audiometric booth environments within subjects and showed no significant difference (paired samples t-test; p . 0.01). DISCUSSION
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iagnostic audiometry in a school environment without a sound-treated booth will require sufficient attenuation and monitoring of ambient noise to ensure the accurate recording of hearing thresholds (Swanepoel, Clark, et al, 2010; Swanepoel, Olusanya, et al, 2010; Maclennan-Smith et al, 2013). In the current study, a recently validated computer-operated audiometer employing passive attenuation using insert earphones covered by circumaural earcups coupled with real-time monitoring of environmental noise was evaluated for air- and bone-conduction threshold measurement in
a natural environment. Double transducer attenuation using insert foam plugs and circumaural earcups produce a significant increase in ambient noise attenuation that may actually exceed typical attenuation for transportable sound booths (Franks, 2001; Berger et al, 2003). Results of the current study confirmed statistically and clinically equivalent hearing thresholds for children tested in a school environment compared to a sound-treated booth. Air-conduction thresholds measured in the natural environment and subsequently in a standard audiometric booth corresponded within typical 5 dB or less testretest limits for thresholds measured in a sound booth (Stuart et al, 1991; Smith-Olinde et al, 2006; Margolis et al, 2010; Swanepoel, Mngemane, et al, 2010; Swanepoel and Biagio, 2011). Average absolute air-conduction threshold differences for the current study (2.1 6 2.9 dB) were within previously reported test-retest absolute average difference values (3.6 6 3.9 dB and 3.5 6 3.8 dB) for the same audiometer (Swanepoel, Mngemane, et al, 2010; Swanepoel and Biagio, 2011). These are also similar to recently reported threshold differences for elderly persons (2.7 6 3.1 dB), using the same audiometer, in Table 3. Absolute Differences in Air- and BoneConduction Thresholds Recorded in the Natural and Audiometric Booth Environments (left and right ears combined) Freq (Hz)
250 500 1000 2000 3000 4000 6000 8000
AC Threshold Correspondence Avg (Abs) 2.7 2.8 2.5 2.2 SD 3.2 3.1 2.9 2.8 n 297 297 297 296 65 dB % 93 94 96 97 BC Threshold Correspondence Avg (Abs) 1.2 1.2 2.1 2.3 SD 2.4 2.5 3.0 2.8 n 291 294 294 294 65 dB % 98 97 94 97
(Natural and 1.8 1.3 2.6 2.4 297 297 98 98 (Natural and 1.6 1.1 2.6 2.4 292 290 98 97
Booth) 1.3 2.3 2.5 3.3 297 296 97 93 Booth)
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Figure 3. Average absolute difference between air-conduction thresholds recorded in the natural and audiometric booth environments (error bars 5 1 SD)
retirement home facilities compared to an audiometric sound booth (Maclennan-Smith et al, 2013). In the current study 96% of threshold comparisons were within 5 dB or better, which is similar to the correspondence (95%) of thresholds recorded using the same audiometer for elderly persons in retirement homes compared to an audiometric sound booth (Maclennan-Smith et al, 2013). This compares favorably to the 88% test-retest correspondence within 5 dB or less reported previously for this audiometer (Swanepoel, Mngemane, et al, 2010). The slightly better correspondence between air-conduction thresholds recorded in the natural and sound booth environments compared with the test-retest differences reported by Swanepoel, Mngemane, et al (2010) may partly be attributed to the omission of 125 Hz as a test frequency in the current study. This low frequency showed a larger test-retest discrepancy than the other frequencies in the Swanepoel, Mngemane, et al (2010) study. The average absolute difference in bone-conduction thresholds recorded in the natural environment and audiometric booth (1.6 62.7 SD) was less than previously reported bone-conduction test-retest differences (Laukli and Fjermedal, 1990; Margolis et al, 2010;
Figure 4. Average absolute difference between bone-conduction thresholds recorded in the natural and audiometric booth environments (error bars 5 1 SD)
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Swanepoel and Biagio, 2011). Reported absolute differences for bone-conduction thresholds in elderly persons (3.4 6 4.3 dB), determined using the same audiometer in retirement facilities compared to an audiometric sound booth, were within typical test-retest differences but slightly larger than the current study differences (Maclennan-Smith et al, 2013). In the current study 97% of bone-conduction thresholds corresponded within 5 dB or less compared to 86% of threshold comparisons between the natural and booth environments recorded for the elderly population (Maclennan-Smith et al, 2013). Improved bone-conduction threshold correspondence in the current study is most likely due, in part, to a floor-effect related to the majority (82%; 316/1755) of thresholds for these children recorded down to 0 dB HL. To assess air- and bone-conduction threshold correspondence without the influence of a possible flooreffect, a comparison was made between thresholds excluding all thresholds recorded at 0 dB in either the natural or booth environments (Table 4). The overall average absolute air-conduction threshold difference (2.1 6 2.9 dB) was similar to the difference when excluding the floor-effect (2.7 6 3.0 dB). The overall absolute bone-conduction threshold difference between environments (1.6 6 2.7 dB) increased when the floor-effect was excluded (3.0 6 2.8 dB). In the bone-conduction results the influence of a floor-effect was confirmed. Correspondence of thresholds between conditions, excluding the floor-effect, was, however, still well within typical test-retest differences previously reported for boneconduction (Laukli and Fjermedal, 1990; Margolis et al, 2010; Swanepoel and Biagio, 2011). Findings from the current study provide evidence that valid diagnostic air- and bone-conduction puretone hearing thresholds can be recorded using a mobile audiometer without a sound booth in school environments. Using insert earphone and circumaural earcup attenuation provides passive control of environmental noise while continuous monitoring of ambient noise provides real-time feedback on extraneous interference. Active noise measurements provide a measure of quality control to monitor noise levels according to the average attenuation provided by the test setup in a typical group of subjects. By employing these attenuation levels, the software can be programmed to monitor ambient noise levels across octave or interoctave levels, according to standards for audiometric test environments (e.g., ANSI, 2008). This type of technology opens up the possibility of mobile diagnostic testing for children immediately after they refer a preschool or school-based hearing screening. This may have a significant impact on the time lost due to referral visits (recommended to be within 3 mo) and could address the typical caveat of preschool and school-based screen follow-up defaults (Flanary et al, 1999; Bamford et al, 2007; Academy, 2011). Directed
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Table 4. Differences in Air- and Bone-Conduction Threshold Comparisons between the Natural and Audiometric Booth Environments for Thresholds >0 dB in Either Condition Freq (Hz)
250
n Avg SD 65 dB %
219 20.2 3.4 99
n Avg SD 65 dB %
7 20.7 1.9 100
500
1000
2000
3000
4000
6000
8000
35 0.1 3.5 97
80 0.6 3.9 98
AC Threshold Differences (Natural and Booth) for Thresholds .0 dB 200 161 130 103 45 0.4 0.2 0.1 20.1 0.6 3.3 2.9 2.8 3.0 2.9 99 99 100 98 98 BC Threshold Differences (Natural and Booth) for Thresholds .0 dB 25 61 109 84 30 20.2 0.1 0.3 20.2 0.2 3.7 3.0 3.0 3.0 2.5 92 100 100 98 97
Note: Thresholds recorded in the booth subtracted from those recorded in the natural environment.
referrals based on diagnostic audiometry could be made for audiological and/or medical intervention without delay. In developing countries where school-based screening may be the first hearing screening children receive, the ability to conduct diagnostic assessments onsite would be invaluable especially when considering the general dearth of audiological equipment and sound booths in these underserved regions (Swanepoel, Clark, et al, 2010; Swanepoel, Olusanya, et al, 2010). In some cases, should valid diagnostic audiometry be completed for children at school and medical conditions ruled out, it may be possible for audiological intervention to be initiated on-site. A cautionary consideration when using this technology is the possible influence of the occlusion effect of the nontest ear when bone-conduction testing outside an audiometric booth is conducted. Deeply inserted insert earphones can minimize the occlusion effect (250–1000 Hz) to a level that is considered to be clinically insignificant (Stenfelt and Goode, 2005), but achieving deep insertion of the insert earphone in young school children may be challenging in certain cases where ear canals are particularly small or in the presence of excessive cerumen or foreign bodies. In these cases, correction values may be necessary to compensate for the occlusion effect (Dean and Martin, 2000). Alternatively, circumaural earphones may be used to avoid the occlusion effect. CONCLUSION
T
he ability to follow-up referrals for hearing screening with valid on-site diagnostic testing may improve the efficacy of current preschool and schoolbased screening programs. Current study findings demonstrate the possibility of determining accurate air- and bone-conduction thresholds using passive attenuation with insert earphones covered by circumaural earcups alongside real-time monitoring of environmental noise through external microphones. The immediate availability of diagnostic pure-tone audiometry following a
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