OtolaryngologyHead and Neck Surgery DECEMBER 1991
VOLUME 105
NUMBER 6
ORIGINAL ARTICLES
Unilateral sensorineural hearing loss rehabilitation D. BRADLEY WELLING, MD, MICHAEL E. GLASSCOCK 111, MD, FACS, CHARLES 1. WOODS, MD, and RONALD C. SHEFFEY, MA, CCC-A, Columbus, Ohio, Nashville, Tennessee, and Syracuse, N e w York
The Audiant Bone Conductor has been heralded as an aid for use in conductive hearing loss; however, its possible use in unilateral sensorineural hearing loss (SNHL) has also been proposed. Between July 1987 and July 1989, profound unilateral sensorineural hearing loss has been rehabilitated in 43 patients using the Xomed Audiant Bone Conductor. Patients who were willing to participate in this clinical trial and who were felt to be good contralateral routing of signals (CROS) aid candidates were selected preoperatively.Audiometric followup, selection criteria, patient satisfaction, and complications are discussed. [OTOLARYNGOL HEAD NECK SURG 1991;105:771.)
Rehabilitation of a profound unilateral sensorineural hearing loss in patients with excellent hearing in the contralateral ear has been somewhat controversial over the last few decades.'-3 Some have argued that rehabilitation is unnecessary. Others contend that certain patients, depending upon their life circumstances, do benefit from contralateral routing of signals (CROS) type hearing aids. Patients with profound unilateral sensorineural hearing loss report several problems, including (1) the inability to hear speech presented to their deaf ear, (2) poor sound localization, and (3) auditory acuity in background noise.
From the Department of Otolaryngology (Dr. Welling), Ohio State University; The Otology Group, P.C. (Dr. Glasscock); the Department of Otolaryngology (Dr. Woods), Syracuse University; and the U.S. Hearing Center (Dr. Sheffey), Nashville. Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, New Orleans, La., Sept. 24-28, 1989. Received for publication Aug. 8, 1990; accepted Feb. 7, 1991. Reprint requests: D. Bradley Welling, MD, Department of Otolaryngology, The Ohio State University, 456 West 10th Ave., Columbus, OH 43210. 23 / 1/28568
The Audiant Bone Conductor (ABC) by XomedTreace (Jacksonville, Fla.) has been used and approved for specific levels of conductive hearing loss, but has also been suggested as a possible CROS aid for the patient with profound unilateral sensorineural hearing 1 0 ~ sVibratory .~ stimulation of the skull is known to transmit sound energy directly to both cochleae, with minimal attenuation between ears. Hough et al.' reported overclosure of an air-bone gap in a patient with a mixed hearing loss by means of this mechanism using the Audiant. The aided postoperative thresholds in the ear with the mixed loss became better than the previous bone level by transmission of sound to the contralateral cochlea. The senior author (M.E.G.) has similar clinical experience with the bone vibrators transferring sound to the better hearing contralateral cochlea in patients with profound unilateral loss. In spite of recent advances in the diagnosis and treatment of acoustic neuromas, many patients still experience complete hearing loss in the affected ear. In an effort to assist patients with this outcome and to independently evaluate the efficacy of the Audiant Bone Conductor as a CROS aid, this clinical trial was initiated. 771
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
772
OtolaryngologyHead and Neck Surgery
WELLING et 01.
Good Ear
Poor Ear
r3 9oo
GOOD EAR NO MUFF
/
POOR EAR NO AID
Fig. 1. Evaluation of the normal hearing ear with head shadow.
METHODS
Between July 1987 and July 1989, 43 patients from the Otology Group, P.C., Nashville, Tennessee, with profound unilateral sensorineural hearing loss were implanted with the ABC. Institutional review board approval was first obtained for this new application of the ABC. Thirty-nine patients were implanted at the time of excision of a cerebellopontine angle tumor. Two patients had undergone labyrinthectomy for Meniere's disease and two patients had profound unilateral loss from other causes. When implanted at the time of acoustic tumor excision, the skin surface was first marked in order to allow coverage of the implant without placing it under a suture line of the scalp flap. The internal device consisted of a titanium-aluminum-vanadium cup and bone screw assembly into which a rare earth magnet is mounted. At the conclusion of the tumor removal, the temporal bone squamosa was drilled and doubly tapped to receive the screw assembly, as recommended by the manufacturer. The scalp directly overlying the magnet was thinned to 6 mm thickness by caliper measurement. Three of our later patients were implanted with the Modified Xomed Audiant, which incorporates a stronger magnet. Patients were offered implantation of the ABC on the basis of their willingness to participate in the investigation and the following audiologic criteria: 1. Unilateral sensorineural hearing loss in the affected ear greater than 90 dB for pure-tone fre-
quencies between 500 and 2,000 Hz; speech reception threshold greater than 90 dB; and speech discrimination score of 20% or less in the ear to be implanted. 2. Pure-tone average of 25 dB HL or better for frequencies 500, 1000, 2000 Hz, and a speech discrimination score of 80% or better in the contralateral ear. Counseling was given relative to the normal expectations for CROS aid applications. Postoperative audiograms were performed at the time of initial fitting and repeated when possible within the first year. Audiometry was performed in a soundtreated booth using the Nicolet Aurora audiometer (Nicolet Manufacturing, Madison, Wis.) calibrated according to the American National Standards Institute (ANSI) criteria. Patients were tested with ear phones to ensure they met the above criteria. The patient was then positioned in a sound field between two speakers located at 90% azimuth at a distance of one meter. Puretone thresholds, speech reception thresholds (SRT), and speech discrimination were then obtained under the following conditons: Test Condition 1. First, the normal hearing ear was evaluated by measuring the pure-tone response to frequencies 250, 500, 1000, 2000, 4000, and 8000 Hz. Speech reception threshold and speech discrimination were likewise recorded'(Fig. 1). Test Condition 2. The speaker directed toward the impaired ear was then used to present the signal. The
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
Volume 105 Number 6 December 1991
Unilateral sensorineural hearing loss rehabilitation 773
Good Ear (Muff)
Poor Ear (No aid)
9oo
GOOD EAR MUFF
/
POOR EAR NO ADD
Fig. 2. Speaker directed toward the impaired ear with the good ear occluded. The Audiont is not in use.
good ear was occluded with a wax plug and again puretone thresholds, speech reception thresholds, and discrimination (with words presented at 50 dB HL) were determined, without the use of the ABC (Fig. 2). Test Coriditioii 3. The ABC was turned on and the signal was presented as in test condition 2 (Fig. 3). Speech discrimination scores were obtained using the Northwestern University Auditory Test 6 , which was stored on cassette tape. Speech discrimination materials were presented at 50 dB HL to simulate normal conversation levels. Mean thresholds were determined and compared between the three test strategies using the paired T test. A patient satisfaction questionnaire was filled out by each patient or obtained in telephone followup. RESULTS Demographics
acoustic tumor removal and the mean SRT in the affected ear preoperatively was 53 dB. The four patients without tumors all had a profound hearing loss (greater than 90 dB PTA and 0% discrimination). A summary of the postoperative audiometric data is presented in Table 1 . The most recent audiogram was used for tabulation. Each pure-tone average, SRT, and % discrimination in condition 1 (no device, no muff) was significantly better than condition 3 (average with ABC and muff) with p < 0.01 by the paired T test. Likewise each mean pure-tone, SRT, and % discrimination condition 3 (ABC with muff) was significantly better ( p < 0.01) than condition 2 (no device with muff) by the paired T test. The average gain was greatest at 2000 Hz (24 dB). Questionnaire Results
Of 43 patients, the mean age in this study was 46.2 years, with a range of 26 to 29 years. The male-tofemale ratio was 3-to-2. Audiometric evaluation was available on 33 patients. Forty-three patients responded to the questionnaire. Audiometric data
Preoperative audiometric data for patients with tumors revealed a pure-tone average of greater than 70 dB in only four of 41 patients. Eighty-one percent of patients were not severely deaf (SRT >70 dB) before
The following responses were obtained to a questionnaire sent to all of the patients. All patients responded; however, not all patients responded to all questions and some questions allowed more than one answer. The questions were divided into two subsetsthe first pertaining to unaided hearing and the second pertaining to hearing with the Xomed Audiant Bone Conductor. Sixty percent of the patients described their ability to hear without use of a hearing device as very good (5%) or good (55%) and 40% felt it wasfair (24%) or
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
OtolaryngologyHead and Neck Surgery
774 WELLING et al
Good Eat (Muff)
Poor Ear (With Audiant)
goo
GOOD EAR MUFF
/
POOR EAR AUDIANT
Fig. 3. Sound-field presentation with the Audiant in use and the good ear occluded. poor (16%). Fifty-seven percent reported poor ability
to determine direction of sound, whereas only 25% felt directionality was good or excellent. Background noise was a problem in 84% of the patients without use of the Audiant. Without the use of a CROS-type aid, 60% of the patients responded that they still felt very comfortable or somewhat comfortable in most social interactions. Forty percent reported feeling less comfortable or very uncomfortable; however, 85% of the patients said they continue to do about the same number of activities socially as they did before becoming unilaterally deaf. In the work place, 90% felt their hearing loss had little or no effect. Twenty-two percent felt their ability to communicate with their co-workers was fair and only 3% poor. All patients were using the at-the-ear (ATE) processor. The mean time since the initial process of fitting was 8.7 months, with a range of 1 week to 24 months. The mean hours of daily use was 2.7 hours. Sixteen patients reported no current use. The most common reasons given for disuse are presented in Table 2. Sixtyfive percent of the respondents felt that the Audiant helped them hear from their bad side, whereas 38% felt that they could sometimes tell when the sound was from the Audiant and 50% said they could never tell when the sound was emanating from the aid. Only 12% felt they could usually or always tell when the sound came from the Audiant. Patients said that the most helpful situation was the increased ability to hear from the bad
side, such as in conversations in the car or while on the telephone. One patient noted that the Audiant helped her start new conversations. The Audiant was considered least helpful in background noise and everyday life. The ability to identify sources of sound was improved in 37% and about the same in 33%. Only 10% felt they could less accurately identify sound sources. When questioned about the cosmesis of the device, 24% indicated it was fine and there were no cosmetic problems. Fifty-two percent felt the device was considerably noticeable and 14% reported that they would not wear it because of its appearance. Finally, when asked to rate the benefit of the Audiant on a one-to-ten scale, with one being very beneficial and ten being no benefit, the mean score was 7.2. It was interesting that 29% of the respondents stated they would definitely recommend a similar aid to patients in the same situation as theirs, 29% would probably recommend a similar aid, 11% were undecided, 11% advised against it, and 20% strongly advised against it. Questions relating to social and work activities revealed 84% were doing about the same number of social activities since their implant and 91% felt they were accomplishing about the same amount of work. Thirtythree percent were more comfortable in social interactions and 13% were less comfortable. Approximately 20% felt they could take on a more responsible or desirable job because of the implant and also indicated that communication with co-workers was improved.
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
Volume 105 Number 6 December 1991
Unilateral sensorineural hearing loss rehabilitation 775
Table 1. Average thresholds db HL, soundfield, signal presented on side o f i m p a i r e d e a r (n = 33) %
Average of no device 270” (no muff) Average of no device 270” (muffed) Average ABC 270” muffed Average gain
4000
8000
SRT
Dlscrlm.
8
16
22
10
99
48
51
57
65
51
37
36
31
27
36
46
32
82
13
17
24
22
19
19
45
250
500
1000
15
12
10
42
49
36
6
Four patients (9%)have experienced mechanical difficulties with the processor. Five (1 1%) have had their magnets removed and two additional patients have requested removal. The reasons given for magnet removal include: poor magnetic attraction, little or no benefit derived from the device, and discomfort from the implant. One patient is a medical student who is interested in radiology and is concerned about interference with MRI . Minor skin irritation, which resolved with removal of the device, was reported by 44% of the respondents. One patient required flap revision for breakdown of the scalp. Magnetic attraction was reported as adequate by 50% and inadequate by 50% of the patients. The three patients with the new Modified Audiant (with the stronger magnet design in the implanted screw assembly) were satisfied with the attraction and our examination confirmed a significant increase in the strength of attraction. DISCUSSION
A number of unilaterally deaf patients in the senior author’s (M.E.G.) practice have been treated over the past 20 years. Until now rehabilitation has been limited to CROS aids to overcome the “head shadow” effect. Studies have shown that low-frequency sounds with longer wave lengths travel around the head more effectively and are less damped than shorter, high-frequency This “head shadow” may cause up to a 10 dB loss from 2000 to 8000 Hz. Like CROS hearing aids, bone conductor hearing aids are known to transfer sound to both cochleae by transmission through the skull. Bone conductors have not been routinely used for CROS aid applications because of the pressure required on the scalp and the cumbersome nature of the equipment involved. Until the Audiant was introduced, a suitable bone conductor aid for the rehabilitation of unilateral profound deafness was not available. On the basis of early favorable rep o r t ~ , ’ this . ~ clinical trial was undertaken to attempt to
2000
Table 2. Reasons for non-use Explanation
Falls offlwon’t stay on Better ear hears “too well”/no help Discomfort Cosmetically unfavorable Wears only in special circumstances
No. of responses
12 9 4 3 4
alleviate some of the problems associated with unilateral deafness. It was not anticipated that directionality would be improved by use of the Audiant because only one functioning cochlea was present. It was hoped that the ability to tell from which direction a sound came would not be adversely affected. Interestingly, from a subjective standpoint, 37% of patients who responded felt that their ability to identify the sources of sound improved with the implant. Some of this would be due to an increased awareness of sound presented to the bad ear. Only 10% felt that their ability to determine the direction of sound was worse with the implant. Although the audiometric data do show considerable gain with the ABC, this unfortunately does not represent the real life condition, but rather an idealized environment for maximizing the potential benefit of the device. On the basis of these data, it might be assumed that some sound energy is transmitted across the skull to the functioning cochlea to help alleviate the “head shadow” effect. Indeed, 65% of the patients in this study responded that it does help them hear sounds from the impaired side. Discrimination scores were also significantly improved with the use of the Audiant when the speech was presented at normal conversation levels (50 dB) with the good ear occluded. Discrimination improved an average of 45% when compared to not using the device with the good ear plugged. It should be noted, however, that with the better ear open in
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
OtolaryngologyHead and Neck Surgery
776 WELLING et al.
a quiet sound booth the discrimination was 99%, even with the sound presented toward the poorer ear. This helps explain why the practical usefulness of the Audiant is somewhat limited by the excellent hearing in the good ear. A significant problem encountered by many of our patients was the weak magnetic attraction of the processor to the implant. Fifty percent of the patients did not feel it was strong enough. This occurred in spite of thinning the scalp flap, as advised by the manufacturer, and using the strongest available magnet in the processor. Three of our later patients were implanted with the Modified Xomed Audiant, which incorporates a new, stronger magnetic material and a larger-diameter magnet. All three were pleased with the attraction and felt it was strong enough without increased skin irritation. In an attempt to stabilize the processor, the postauricular strut was used in all of our patients. McKinnon and Sheaffer* have recently suggested a clear lucite silhouette ear mold be attached to the strut to further stabilize the processor in children. This might also be applied in the active adult or those with weak attraction to prevent loss or damage to the processor. Many patients who wear glasses noted difficulty with removing their glasses and knocking off the implant. A physician noted the same problem with stethoscope use. Several patients indicated that the attraction seemed to improve with time. A thinning of the scalp may occur with daily pressure between the magnet and the processor. Cosmesis also proved to be a detriment to wearing the device in some patients who believed they obtained a significant benefit from the device. Patients who chose shorter hairstyles, including women, were more likely to have a problem. Several patients who have now tried a CROS aid related that the volume was superior but the tonal quality more mechanical than the Audiant. If the output of the processor could be boosted and improved auditory quality maintained, the Audiant may be a reasonable alternative to conventional CROS aids. It is likely that the most significant finding in this study is the subjective overall benefit rating of 7.2 (on a I to 10 scale, with 10 being equal to no benefit) and low total use time (mean daily use was 2.7 hours, with 57% using the device 1 hour or less per day). Surprisingly, 58% of those using the device would still “definitely” or “possibly” recommend the Audiant to others in similar circumstances.
SUMMARY
The proposed use of a bone conductor hearing aid for the unilaterally profoundly deaf has not, in this study, been shown to be effective. Although effective in some cases, the implantation of the Audiant Bone Conductor cannot be recommended routinely for patients at the time of acoustic tumor surgery. The greater proportion of our patients found it of little benefit to them. A better selection process might improve expectations and results. For example, the patient should first have the opportunity to identify situations in his or her own lifestyle that might require CROS-type amplification after being back in his or her normal environment as a unilateral listener. Then, for patients who feel they need amplification from the impaired side, a conventional CROS aid or conventional bone aid trial could first be carried out. Although the ABC proved to transfer sound from the poorer ear to the good ear by way of bone conduction as anticipated, a more powerful driver and improved magnetic attraction may be necessary to make the Audiant useful in the CROS aid application. Comparison with CROS aids and different audiologic testing strategies should provide useful information, as should long-term followup of the current cohort. These studies are necessary to clarify the place of bone conduction hearing aids in the rehabilitation of profound unilateral hearing loss.
REFERENCES
I . Harford E, Bany J . A rehabilitative approach to the problem of unilateral hearing impairment: the contralateral routing of signals (CROS). J Speech Hear Dis 1965;30:121-38. 2. Harford E, Dodds E. Clinical application of CROS. Arch Otolaryngol 1966;83:73-82. 3 Harford E. Is a hearing aid ever justified in unilateral hearing loss? Otolaryngol Clin North Am 1969:153-73. 4 Hough J. Vernon J, Johnson B, et al. Experiences with implantation hearing devices and a presentation of a new device. Ann Otol Rhinol Laryngol 1986;95:60-5. 5. Hough J, Himelich T, Johnson B. Implantable bone conduction hearing device: Audiant Bone Conductor. Update on our experiences. Ann Otol Rhinol Laryngol 1986;95:498-504. 6. Sivian L, White S . On minimum audible sound fields. J Acoust SOCAmer 1933;4:288-321. 7. Wiener F. On the diffraction of a progressive sound wave by the human head. J Amer Speech Assoc 1947;19:143-6. 8. McKennan K, Sheaffer D. Anchoring device for the Xomed Audiant at-the-ear bone conductor. Laryngoscope 1989;99:766-7.
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
VOLUME 105
NUMBER 6
ORIGINAL ARTICLES
Unilateral sensorineural hearing loss rehabilitation D. BRADLEY WELLING, MD, MICHAEL E. GLASSCOCK 111, MD, FACS, CHARLES 1. WOODS, MD, and RONALD C. SHEFFEY, MA, CCC-A, Columbus, Ohio, Nashville, Tennessee, and Syracuse, N e w York
The Audiant Bone Conductor has been heralded as an aid for use in conductive hearing loss; however, its possible use in unilateral sensorineural hearing loss (SNHL) has also been proposed. Between July 1987 and July 1989, profound unilateral sensorineural hearing loss has been rehabilitated in 43 patients using the Xomed Audiant Bone Conductor. Patients who were willing to participate in this clinical trial and who were felt to be good contralateral routing of signals (CROS) aid candidates were selected preoperatively.Audiometric followup, selection criteria, patient satisfaction, and complications are discussed. [OTOLARYNGOL HEAD NECK SURG 1991;105:771.)
Rehabilitation of a profound unilateral sensorineural hearing loss in patients with excellent hearing in the contralateral ear has been somewhat controversial over the last few decades.'-3 Some have argued that rehabilitation is unnecessary. Others contend that certain patients, depending upon their life circumstances, do benefit from contralateral routing of signals (CROS) type hearing aids. Patients with profound unilateral sensorineural hearing loss report several problems, including (1) the inability to hear speech presented to their deaf ear, (2) poor sound localization, and (3) auditory acuity in background noise.
From the Department of Otolaryngology (Dr. Welling), Ohio State University; The Otology Group, P.C. (Dr. Glasscock); the Department of Otolaryngology (Dr. Woods), Syracuse University; and the U.S. Hearing Center (Dr. Sheffey), Nashville. Presented at the Annual Meeting of the American Academy of Otolaryngology-Head and Neck Surgery, New Orleans, La., Sept. 24-28, 1989. Received for publication Aug. 8, 1990; accepted Feb. 7, 1991. Reprint requests: D. Bradley Welling, MD, Department of Otolaryngology, The Ohio State University, 456 West 10th Ave., Columbus, OH 43210. 23 / 1/28568
The Audiant Bone Conductor (ABC) by XomedTreace (Jacksonville, Fla.) has been used and approved for specific levels of conductive hearing loss, but has also been suggested as a possible CROS aid for the patient with profound unilateral sensorineural hearing 1 0 ~ sVibratory .~ stimulation of the skull is known to transmit sound energy directly to both cochleae, with minimal attenuation between ears. Hough et al.' reported overclosure of an air-bone gap in a patient with a mixed hearing loss by means of this mechanism using the Audiant. The aided postoperative thresholds in the ear with the mixed loss became better than the previous bone level by transmission of sound to the contralateral cochlea. The senior author (M.E.G.) has similar clinical experience with the bone vibrators transferring sound to the better hearing contralateral cochlea in patients with profound unilateral loss. In spite of recent advances in the diagnosis and treatment of acoustic neuromas, many patients still experience complete hearing loss in the affected ear. In an effort to assist patients with this outcome and to independently evaluate the efficacy of the Audiant Bone Conductor as a CROS aid, this clinical trial was initiated. 771
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
772
OtolaryngologyHead and Neck Surgery
WELLING et 01.
Good Ear
Poor Ear
r3 9oo
GOOD EAR NO MUFF
/
POOR EAR NO AID
Fig. 1. Evaluation of the normal hearing ear with head shadow.
METHODS
Between July 1987 and July 1989, 43 patients from the Otology Group, P.C., Nashville, Tennessee, with profound unilateral sensorineural hearing loss were implanted with the ABC. Institutional review board approval was first obtained for this new application of the ABC. Thirty-nine patients were implanted at the time of excision of a cerebellopontine angle tumor. Two patients had undergone labyrinthectomy for Meniere's disease and two patients had profound unilateral loss from other causes. When implanted at the time of acoustic tumor excision, the skin surface was first marked in order to allow coverage of the implant without placing it under a suture line of the scalp flap. The internal device consisted of a titanium-aluminum-vanadium cup and bone screw assembly into which a rare earth magnet is mounted. At the conclusion of the tumor removal, the temporal bone squamosa was drilled and doubly tapped to receive the screw assembly, as recommended by the manufacturer. The scalp directly overlying the magnet was thinned to 6 mm thickness by caliper measurement. Three of our later patients were implanted with the Modified Xomed Audiant, which incorporates a stronger magnet. Patients were offered implantation of the ABC on the basis of their willingness to participate in the investigation and the following audiologic criteria: 1. Unilateral sensorineural hearing loss in the affected ear greater than 90 dB for pure-tone fre-
quencies between 500 and 2,000 Hz; speech reception threshold greater than 90 dB; and speech discrimination score of 20% or less in the ear to be implanted. 2. Pure-tone average of 25 dB HL or better for frequencies 500, 1000, 2000 Hz, and a speech discrimination score of 80% or better in the contralateral ear. Counseling was given relative to the normal expectations for CROS aid applications. Postoperative audiograms were performed at the time of initial fitting and repeated when possible within the first year. Audiometry was performed in a soundtreated booth using the Nicolet Aurora audiometer (Nicolet Manufacturing, Madison, Wis.) calibrated according to the American National Standards Institute (ANSI) criteria. Patients were tested with ear phones to ensure they met the above criteria. The patient was then positioned in a sound field between two speakers located at 90% azimuth at a distance of one meter. Puretone thresholds, speech reception thresholds (SRT), and speech discrimination were then obtained under the following conditons: Test Condition 1. First, the normal hearing ear was evaluated by measuring the pure-tone response to frequencies 250, 500, 1000, 2000, 4000, and 8000 Hz. Speech reception threshold and speech discrimination were likewise recorded'(Fig. 1). Test Condition 2. The speaker directed toward the impaired ear was then used to present the signal. The
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
Volume 105 Number 6 December 1991
Unilateral sensorineural hearing loss rehabilitation 773
Good Ear (Muff)
Poor Ear (No aid)
9oo
GOOD EAR MUFF
/
POOR EAR NO ADD
Fig. 2. Speaker directed toward the impaired ear with the good ear occluded. The Audiont is not in use.
good ear was occluded with a wax plug and again puretone thresholds, speech reception thresholds, and discrimination (with words presented at 50 dB HL) were determined, without the use of the ABC (Fig. 2). Test Coriditioii 3. The ABC was turned on and the signal was presented as in test condition 2 (Fig. 3). Speech discrimination scores were obtained using the Northwestern University Auditory Test 6 , which was stored on cassette tape. Speech discrimination materials were presented at 50 dB HL to simulate normal conversation levels. Mean thresholds were determined and compared between the three test strategies using the paired T test. A patient satisfaction questionnaire was filled out by each patient or obtained in telephone followup. RESULTS Demographics
acoustic tumor removal and the mean SRT in the affected ear preoperatively was 53 dB. The four patients without tumors all had a profound hearing loss (greater than 90 dB PTA and 0% discrimination). A summary of the postoperative audiometric data is presented in Table 1 . The most recent audiogram was used for tabulation. Each pure-tone average, SRT, and % discrimination in condition 1 (no device, no muff) was significantly better than condition 3 (average with ABC and muff) with p < 0.01 by the paired T test. Likewise each mean pure-tone, SRT, and % discrimination condition 3 (ABC with muff) was significantly better ( p < 0.01) than condition 2 (no device with muff) by the paired T test. The average gain was greatest at 2000 Hz (24 dB). Questionnaire Results
Of 43 patients, the mean age in this study was 46.2 years, with a range of 26 to 29 years. The male-tofemale ratio was 3-to-2. Audiometric evaluation was available on 33 patients. Forty-three patients responded to the questionnaire. Audiometric data
Preoperative audiometric data for patients with tumors revealed a pure-tone average of greater than 70 dB in only four of 41 patients. Eighty-one percent of patients were not severely deaf (SRT >70 dB) before
The following responses were obtained to a questionnaire sent to all of the patients. All patients responded; however, not all patients responded to all questions and some questions allowed more than one answer. The questions were divided into two subsetsthe first pertaining to unaided hearing and the second pertaining to hearing with the Xomed Audiant Bone Conductor. Sixty percent of the patients described their ability to hear without use of a hearing device as very good (5%) or good (55%) and 40% felt it wasfair (24%) or
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
OtolaryngologyHead and Neck Surgery
774 WELLING et al
Good Eat (Muff)
Poor Ear (With Audiant)
goo
GOOD EAR MUFF
/
POOR EAR AUDIANT
Fig. 3. Sound-field presentation with the Audiant in use and the good ear occluded. poor (16%). Fifty-seven percent reported poor ability
to determine direction of sound, whereas only 25% felt directionality was good or excellent. Background noise was a problem in 84% of the patients without use of the Audiant. Without the use of a CROS-type aid, 60% of the patients responded that they still felt very comfortable or somewhat comfortable in most social interactions. Forty percent reported feeling less comfortable or very uncomfortable; however, 85% of the patients said they continue to do about the same number of activities socially as they did before becoming unilaterally deaf. In the work place, 90% felt their hearing loss had little or no effect. Twenty-two percent felt their ability to communicate with their co-workers was fair and only 3% poor. All patients were using the at-the-ear (ATE) processor. The mean time since the initial process of fitting was 8.7 months, with a range of 1 week to 24 months. The mean hours of daily use was 2.7 hours. Sixteen patients reported no current use. The most common reasons given for disuse are presented in Table 2. Sixtyfive percent of the respondents felt that the Audiant helped them hear from their bad side, whereas 38% felt that they could sometimes tell when the sound was from the Audiant and 50% said they could never tell when the sound was emanating from the aid. Only 12% felt they could usually or always tell when the sound came from the Audiant. Patients said that the most helpful situation was the increased ability to hear from the bad
side, such as in conversations in the car or while on the telephone. One patient noted that the Audiant helped her start new conversations. The Audiant was considered least helpful in background noise and everyday life. The ability to identify sources of sound was improved in 37% and about the same in 33%. Only 10% felt they could less accurately identify sound sources. When questioned about the cosmesis of the device, 24% indicated it was fine and there were no cosmetic problems. Fifty-two percent felt the device was considerably noticeable and 14% reported that they would not wear it because of its appearance. Finally, when asked to rate the benefit of the Audiant on a one-to-ten scale, with one being very beneficial and ten being no benefit, the mean score was 7.2. It was interesting that 29% of the respondents stated they would definitely recommend a similar aid to patients in the same situation as theirs, 29% would probably recommend a similar aid, 11% were undecided, 11% advised against it, and 20% strongly advised against it. Questions relating to social and work activities revealed 84% were doing about the same number of social activities since their implant and 91% felt they were accomplishing about the same amount of work. Thirtythree percent were more comfortable in social interactions and 13% were less comfortable. Approximately 20% felt they could take on a more responsible or desirable job because of the implant and also indicated that communication with co-workers was improved.
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
Volume 105 Number 6 December 1991
Unilateral sensorineural hearing loss rehabilitation 775
Table 1. Average thresholds db HL, soundfield, signal presented on side o f i m p a i r e d e a r (n = 33) %
Average of no device 270” (no muff) Average of no device 270” (muffed) Average ABC 270” muffed Average gain
4000
8000
SRT
Dlscrlm.
8
16
22
10
99
48
51
57
65
51
37
36
31
27
36
46
32
82
13
17
24
22
19
19
45
250
500
1000
15
12
10
42
49
36
6
Four patients (9%)have experienced mechanical difficulties with the processor. Five (1 1%) have had their magnets removed and two additional patients have requested removal. The reasons given for magnet removal include: poor magnetic attraction, little or no benefit derived from the device, and discomfort from the implant. One patient is a medical student who is interested in radiology and is concerned about interference with MRI . Minor skin irritation, which resolved with removal of the device, was reported by 44% of the respondents. One patient required flap revision for breakdown of the scalp. Magnetic attraction was reported as adequate by 50% and inadequate by 50% of the patients. The three patients with the new Modified Audiant (with the stronger magnet design in the implanted screw assembly) were satisfied with the attraction and our examination confirmed a significant increase in the strength of attraction. DISCUSSION
A number of unilaterally deaf patients in the senior author’s (M.E.G.) practice have been treated over the past 20 years. Until now rehabilitation has been limited to CROS aids to overcome the “head shadow” effect. Studies have shown that low-frequency sounds with longer wave lengths travel around the head more effectively and are less damped than shorter, high-frequency This “head shadow” may cause up to a 10 dB loss from 2000 to 8000 Hz. Like CROS hearing aids, bone conductor hearing aids are known to transfer sound to both cochleae by transmission through the skull. Bone conductors have not been routinely used for CROS aid applications because of the pressure required on the scalp and the cumbersome nature of the equipment involved. Until the Audiant was introduced, a suitable bone conductor aid for the rehabilitation of unilateral profound deafness was not available. On the basis of early favorable rep o r t ~ , ’ this . ~ clinical trial was undertaken to attempt to
2000
Table 2. Reasons for non-use Explanation
Falls offlwon’t stay on Better ear hears “too well”/no help Discomfort Cosmetically unfavorable Wears only in special circumstances
No. of responses
12 9 4 3 4
alleviate some of the problems associated with unilateral deafness. It was not anticipated that directionality would be improved by use of the Audiant because only one functioning cochlea was present. It was hoped that the ability to tell from which direction a sound came would not be adversely affected. Interestingly, from a subjective standpoint, 37% of patients who responded felt that their ability to identify the sources of sound improved with the implant. Some of this would be due to an increased awareness of sound presented to the bad ear. Only 10% felt that their ability to determine the direction of sound was worse with the implant. Although the audiometric data do show considerable gain with the ABC, this unfortunately does not represent the real life condition, but rather an idealized environment for maximizing the potential benefit of the device. On the basis of these data, it might be assumed that some sound energy is transmitted across the skull to the functioning cochlea to help alleviate the “head shadow” effect. Indeed, 65% of the patients in this study responded that it does help them hear sounds from the impaired side. Discrimination scores were also significantly improved with the use of the Audiant when the speech was presented at normal conversation levels (50 dB) with the good ear occluded. Discrimination improved an average of 45% when compared to not using the device with the good ear plugged. It should be noted, however, that with the better ear open in
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
OtolaryngologyHead and Neck Surgery
776 WELLING et al.
a quiet sound booth the discrimination was 99%, even with the sound presented toward the poorer ear. This helps explain why the practical usefulness of the Audiant is somewhat limited by the excellent hearing in the good ear. A significant problem encountered by many of our patients was the weak magnetic attraction of the processor to the implant. Fifty percent of the patients did not feel it was strong enough. This occurred in spite of thinning the scalp flap, as advised by the manufacturer, and using the strongest available magnet in the processor. Three of our later patients were implanted with the Modified Xomed Audiant, which incorporates a new, stronger magnetic material and a larger-diameter magnet. All three were pleased with the attraction and felt it was strong enough without increased skin irritation. In an attempt to stabilize the processor, the postauricular strut was used in all of our patients. McKinnon and Sheaffer* have recently suggested a clear lucite silhouette ear mold be attached to the strut to further stabilize the processor in children. This might also be applied in the active adult or those with weak attraction to prevent loss or damage to the processor. Many patients who wear glasses noted difficulty with removing their glasses and knocking off the implant. A physician noted the same problem with stethoscope use. Several patients indicated that the attraction seemed to improve with time. A thinning of the scalp may occur with daily pressure between the magnet and the processor. Cosmesis also proved to be a detriment to wearing the device in some patients who believed they obtained a significant benefit from the device. Patients who chose shorter hairstyles, including women, were more likely to have a problem. Several patients who have now tried a CROS aid related that the volume was superior but the tonal quality more mechanical than the Audiant. If the output of the processor could be boosted and improved auditory quality maintained, the Audiant may be a reasonable alternative to conventional CROS aids. It is likely that the most significant finding in this study is the subjective overall benefit rating of 7.2 (on a I to 10 scale, with 10 being equal to no benefit) and low total use time (mean daily use was 2.7 hours, with 57% using the device 1 hour or less per day). Surprisingly, 58% of those using the device would still “definitely” or “possibly” recommend the Audiant to others in similar circumstances.
SUMMARY
The proposed use of a bone conductor hearing aid for the unilaterally profoundly deaf has not, in this study, been shown to be effective. Although effective in some cases, the implantation of the Audiant Bone Conductor cannot be recommended routinely for patients at the time of acoustic tumor surgery. The greater proportion of our patients found it of little benefit to them. A better selection process might improve expectations and results. For example, the patient should first have the opportunity to identify situations in his or her own lifestyle that might require CROS-type amplification after being back in his or her normal environment as a unilateral listener. Then, for patients who feel they need amplification from the impaired side, a conventional CROS aid or conventional bone aid trial could first be carried out. Although the ABC proved to transfer sound from the poorer ear to the good ear by way of bone conduction as anticipated, a more powerful driver and improved magnetic attraction may be necessary to make the Audiant useful in the CROS aid application. Comparison with CROS aids and different audiologic testing strategies should provide useful information, as should long-term followup of the current cohort. These studies are necessary to clarify the place of bone conduction hearing aids in the rehabilitation of profound unilateral hearing loss.
REFERENCES
I . Harford E, Bany J . A rehabilitative approach to the problem of unilateral hearing impairment: the contralateral routing of signals (CROS). J Speech Hear Dis 1965;30:121-38. 2. Harford E, Dodds E. Clinical application of CROS. Arch Otolaryngol 1966;83:73-82. 3 Harford E. Is a hearing aid ever justified in unilateral hearing loss? Otolaryngol Clin North Am 1969:153-73. 4 Hough J. Vernon J, Johnson B, et al. Experiences with implantation hearing devices and a presentation of a new device. Ann Otol Rhinol Laryngol 1986;95:60-5. 5. Hough J, Himelich T, Johnson B. Implantable bone conduction hearing device: Audiant Bone Conductor. Update on our experiences. Ann Otol Rhinol Laryngol 1986;95:498-504. 6. Sivian L, White S . On minimum audible sound fields. J Acoust SOCAmer 1933;4:288-321. 7. Wiener F. On the diffraction of a progressive sound wave by the human head. J Amer Speech Assoc 1947;19:143-6. 8. McKennan K, Sheaffer D. Anchoring device for the Xomed Audiant at-the-ear bone conductor. Laryngoscope 1989;99:766-7.
Downloaded from oto.sagepub.com at University of Sussex Library on September 11, 2015
