A Case for Real Ear Measures
BA is scheduled for a comprehensive audiological examination and hearing aid evaluation (HAE). He obtained bilateral receiver-in-the-canal (RIC) hearing aids 3 to 4 years ago from a large retail chain. He notices benefit with the hearing aids, but believes he is not hearing as well as he should, particularly in noisy listening situations. Real ear insertion gain (REIG) measures revealed minimal insertion gain bilaterally when compared with the prescribed National Acoustic Laboratories’ non-linear fitting formula version 1 (NAL-NL1).
BA is a 68-year-old male who was initially examined by an otologist due to BA reporting decreased hearing in the right ear following an upper respiratory tract infection that began two months ago. BA reported hearing loss since middle school due to an extensive history of ear infections as a child. BA also reported a number of myringotomies that included insertion of pressure-equalization tubes. BA stated that his right ear had better hearing until the upper respiratory tract infection. BA started wearing bilateral RIC hearing aids three to four years ago, and he stated he had a family history of hearing loss that included his grandfather. He had a significant history of noise exposure as a result of working in construction for approximately 40 years.
Otoscopy for the right ear revealed amber fluid behind the tympanic membrane and the tympanic membrane was retracted. Otoscopy for the left ear revealed that the tympanic membrane was also retracted, but fluid was not present behind the tympanic membrane. The otologist’s examination reported right chronic otitis media, and BA’s hearing loss was thought to be due to the combination of presbycusis, excessive exposure to noise, and genetics. The otologist recommended a follow-up appointment in one month with a repeat audiological examination and a head computed tomographic (CT) scan. The otologist also recommended using an Otovent (Abigo Medical AB, Askim, Sweden). The Otovent consists of a nose plug and latex balloon. The patient pinches one nostril shut and puts the Otovent in the other nostril and, by blowing air through the nose, inflates the latex balloon. Once the balloon is inflated, the air from the balloon reenters the nostril, creating positive pressure, the patient swallows and the eustachian tube opens allowing fluid to drain from the middle ear.
When BA returned in one month, he reported an immediate improvement in hearing in the right ear after using the Otovent. Along with an audiological examination, the patient was also scheduled for an HAE. Results of the audiological examination (Fig. 55.1) revealed hearing was within normal limits for the right ear from 250 to 1000 Hz and precipitously fell to a moderate to moderately-severe sensorineural hearing loss from 1500 to 8000 Hz. Results in the left ear revealed hearing to be within normal limits at 250 Hz and sloping to a slight mixed hearing loss from 500 to 1000 Hz, then precipitously falling to a moderate to moderately-severe sensorineural hearing loss from 1500 to 8000 Hz. Speech recognition thresholds (SRTs) were normal in the right ear and revealed a slight loss in the ability to receive speech in the left ear. Word recognition scores (WRSs) using the Northwestern University Test Number 6 (NU-6) word lists with a recorded female talker revealed normal ability to recognize speech bilaterally (92% bilaterally). Immittance audiometry was performed and revealed a normal tympanogram in the right ear and excessive negative pressure (− 105 daPa) in the left ear indicating the possible presence of a malfunctioning eustachian tube. Acoustic reflex thresholds (ARTs) for right ipsilateral stimulation were within normal limits from 500 to 2000 Hz and absent at 4000 Hz and for left ipsilateral stimulation were elevated at 1000 Hz, and absent at 500 and 2000 to 4000 Hz. ARTs for right contra lateral stimulation were elevated at 500 Hz and absent from 1000 to 4000 Hz and for left contralateral stimulation were within normal limits at 1000 Hz, elevated at 2000 Hz, and absent at 500 and 4000 Hz. Reflex decay could only be performed for left contralateral stimulation at 1000 Hz, because the right contralateral ART at 1000 Hz and left contralateral ART at 500 Hz were absent and the right contralateral ART at 500 Hz was elevated; therefore, the intensity of the stimulus could not be made loud enough (+ 10 dB SL) to perform reflex decay. The result of reflex decay for left contralateral at 1000 Hz was negative.
As mentioned earlier, BA wore bilateral RIC hearing aids with directional microphones and open domes. He purchased the hearing aids from a large chain, which was an approximately four hour drive away due to the low cost of the hearing aids compared with other clinics in his area. BA thought he received benefit from the hearing aids, but was disappointed with how he understands speech in noisy listening situations. BA questioned if his ability to understand speech in background noise could be improved.
What recommendations would a clinician provide BA about his hearing aids?
The patient could be counseled about considering more current hearing aid technology or reprogramming his current hearing aids. BA has had his hearing aids for three to four years and he may or may not notice improved benefit from more current hearing aid technology. Another option is to determine the amount of amplification being provided via REMs and to reprogram BA’s hearing aids to improve benefit if the hearing aids are not providing adequate amplification. BA’s hearing may also have changed since he purchased his current hearing aids, which could be a reason why BA is not hearing as well.
Are differences in gain/output to be expected between a manufacturer’s “First-Fit” compared with using real ear measures (REMs) to program hearing aids?
Several studies have reported significant differences between the manufacturer’s First-Fit and a prescriptive fitting formula, such as NAL-NL1. For example, Aazh and Moore (2007) reported a difference of ± 10 dB from the NAL-NL1 prescriptive target at one or more frequencies between 250 and 4000 Hz using the manufacturer’s First-Fit for 64% of ears that were measured. Another study by Abram et al reported higher benefit scores on the Abbreviated Profile of Hearing Aid Benefit (APHAB) and that more experienced hearing aid users preferred hearing aids programmed using REMs to NAL-NL1 than hearing aids fit according to the manufacturer’s prescribed First-Fit. Also, a MarkeTrak report revealed that performing verification and validation during the hearing aid fitting process resulted in 1.2 fewer visits compared with not performing these measures. Verification refers to measures that confirm the hearing aid is working properly and fit appropriately for the patient (i.e., electroacoustic performance, REMs, etc.), and validation refers to measures that confirm the patient is obtaining/perceiving benefit from the hearing aid (i.e., aided speech in noise measures, questionnaires, etc.).
What considerations need to be taken into account when performing REMs on an open-fit hearing aid?
One of the most important considerations is the use of the reference microphone. There are two methods to calibrate the loudspeaker of a REM system to ensure that signals (in dB sound pressure level [SPL]) from the loudspeaker to the reference microphone placed near the ear is at the stated input level when the signals reach the microphones of the hearing aid. One method is the modified pressure method with concurrent equalization. Using this method, the reference microphone is actively analyzing in real time the output (dB SPL) of the loudspeaker to the reference microphone and adjusting the output based on patient movement so that the input level near the microphones of the hearing aid remains constant. The other method is the modified pressure method with stored equalization. Using this method, the reference microphone is only activated when the reference and probe microphones are leveled and when measuring the unaided response of the ear. Then the reference microphone is deactivated during aided measures, and it is critical that the patient hold his or her head still. The patient should be instructed to look straight ahead at the loudspeaker and to keep the head still for all measures; the audiologist must keep an eye on the patient to ensure this occurs.
When an open fitting is being verified in the aided condition, amplified sound could escape from the ear canal and reach the reference microphone. A confounding variable can occur with the modified pressure method with concurrent equalization because the amplified sound escaping the ear canal could reach the reference microphone causing the loudspeaker output to decrease due to the perceived higher output received by the reference microphone. This could result in the audiologist thinking there is less gain/output than is actually being provided by the hearing aid. The gain/output of the hearing aid would then be programmed to be increased to compensate for this in order to match the prescribed target. This could lead to overamplification of approximately 5 dB, particularly from approximately 1000 to 4000 Hz. Studies have reported that the concern of amplified sound interfering with the reference test microphone primarily occurred when the prescriptive target prescribed ≥ 25 dB of gain. Otherwise, ≤ 25 dB of gain had minimal impact on the reference microphone and the accuracy of the measured gain to target. Therefore, for open-fit hearing aid fittings requiring ≥ 25 dB of gain, the modified pressure method with stored equalization is recommended.
BA was counseled on reprogramming the hearing aids he purchased about three to four years ago or the possibility of obtaining new hearing aids. In this case, the hearing aids would have to be reprogrammed where the patient purchased his hearing aids due to the proprietary software required to program the hearing aids. If the software was not proprietary, but the audiologist did not have the software or cables to program the hearing aids, the audiologist could call the manufacturer to order the appropriate software and cables for the hearing aids to program them. Because the patient had the hearing aids for only three to four years, the option of verifying the magnitude of amplification the patient was receiving from his hearing aids using REIG measures in relation to the NAL-NL1 prescriptive fitting formula was discussed. If it was determined that the hearing aids were not providing appropriate amplification, the patient could use this information to return to the clinic where he purchased his hearing aids for reprogramming. A local office of the retail chain where the patient purchased his hearing aids recently opened close to his home, and the patient would not have to drive as far for reprogramming. BA was counseled that he would be charged a standard rate per every 15 minutes of REMs because he had purchased his hearing aids from another clinic. The patient decided he would like to briefly learn about new hearing aid technology and also decided to pay to have REMs performed on his hearing aids. The improvements in hearing aid technology since he purchased his current hearing aids along with hearing assistive technology (HAT) were discussed prior to REMs.
Prior to REMs, the hearing aids were dehumidified, and the wax guard and dome were examined to make sure each was free of wax. Electroacoustic analysis was performed using the Frye FONIX 6500® Hearing Aid Analyzer (Frye Electronics, Inc.©, Tigard, OR) using ANSI S3.22–1996 and a completely-in-the-canal (CIC) coupler. Results revealed reference test gain of 20.5 dB in the right ear and 19.0 dB in the left ear, which showed that the patient’s hearing aids were operating. The patient’s audiological data were placed into the Frye FONIX 8000 Hearing Aid Analyzer®, and the NAL-NL1 target was corrected for binaural and channel summation (six channels). REIG measures were performed using a 65 dB SPL input level of the DigiSpeech (intermittent speech-weighted) signal (Fig. 55.2). Results revealed minimal gain bilaterally compared with NAL-NL1. One possible reason for the differences in coupler versus real ear gain may be due to the coupling of the hearing aid to the ear, because the hearing aid receiver had an open dome and loosely fit at the outside of his ear canal; this may allow the amplified sound to leak out of his ear canal. Another reason may be due to the acoustics of BA’s ear canal (i.e., large ear canal, large real ear unaided gain [REUG], etc.) and the need for more gain to compensate for this. It was noted that BA had a large REUG (20 dB bilaterally around 2500 Hz), which means the hearing aid would need to provide more amplification to overcome the insertion loss of the hearing aid to meet the NAL-NL1 target, although it is expected that there would be minimal insertion loss with an open-fit hearing aid.
Although the reference microphone was not deactivated for testing, it is expected that having the reference microphone activated would not have resulted in poorer than measured REMs because the prescribed gain was less than 25 dB. The patient was counseled on the limited amount of amplification he is receiving with his hearing aids. He was provided with a copy of the results, as well as instructions on the frequency regions (1000 to 6000 Hz in the right ear and 1000 to 6000 Hz in the left ear) that needed more gain in order to provide appropriate amplification according to NAL-NL1.
BA returned to the otologist two weeks later. It was noted that the CT scan was normal, except for slight fluid in the right mastoid. A medical examination revealed that BA no longer had retracted tympanic membranes or fluid behind his right eardrum. BA reported he was working with the dispensing professional at the large retail chain to have his hearing aids reprogrammed to a more appropriate level for his hearing loss.
Audiologists should provide patients with information (i.e., performance of REMs, electroacoustic measures, charges for visits, etc.) on what to seek when selecting a facility to obtain hearing aids so patients will receive evidence-based practice care and maximum benefit from their hearing aid(s).
2 Aazh H, Moore BC, Prasher D. Real ear measurement methods for open fit hearing aids: modified pressure concurrent equalization (MPCE) versus modified pressure stored equalization (MPSE). Int J Audiol. 2012;51(2):103-107.
5 American Speech-Language-Hearing Association. Guidelines for hearing aid fitting for adults. 1998. www.asha.org/policy/GL1998-00012.htm
8 Kochkin S. MarkeTrak VIII: reducing patient visits through verification and validation. Hear J 2011. http://www.hearingreview.com/products/17112-marketrak-viii-reducing-patient-visits-through-verification-amp-validation