Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
J Am Acad Audiol 3 : 60-65 (1992) Real Ear Unaided Responses in Ears with Tympanic Membrane Perforations Colleen L. Moryl* Jeffrey L. Danhauer* Joseph R. DiBartolomeot Abstract This study evaluated 13 adult patients with tympanic membrane (TM) perforations in one or both ears . Probe microphone real ear unaided responses (REURs) for mean peakfrequency and peak dB gain showed no substantial differences among patients, across ears with intact TMs, ears with TM perforations (regardless of size), or between measures taken before and after closure of the perforations . Inspection of individual differences in the patients' REURs, however, produced an interesting finding. The REURs of ears having small TM perforations did not differ from those with intact TMs, but the REURs for ears having larger perforations consistently revealed bimodal responses (two prominent peaks separated by a valley of at least 10 dB lower gain) . Thus, size of the perforation affected the REURs. Key Words: Hearing aids, real ear probe microphone measures, real ear unaided response (REUR), tympanic membrane perforations ir-conduction hearing aids are frequently considered for patients with persistA ent tympanic membrane (TM) perforations when surgery is not an option . The use of probe microphone measures for hearing aid assessment has become routine in clinic and research settings . Measurement of the real ear unaided response (REUR) "refers to the measured frequency response in dB SPL with a probe microphone at a specified point within the unaided, unoccluded external auditory canal for a specified sound field" (Schweitzer et al, 1990) . The REUR is often the first measure taken when fitting hearing aids by evaluating the real ear insertion response (REIR) with probe microphone systems. The REUR may also be helpful in determining if physical and acoustic characteristics of the ear canal are altered by TM perforations and whether corresponding compensations must 'Department of Speech and Hearing Sciences, University of California, Santa Barbara, California t The Ear Foundation, Santa Barbara ; and Department of Otolaryngology, University of California, Los Angeles, California Reprint requests : Jeffrey L . Danhauer, Department of Speech and Hearing Sciences, Snidecor Hall, University of California Santa Barbara, Santa Barbara, CA 93106 60 be made in fitting hearing aids to patients having perforations . Generally, an unoccluded ear without a TM perforation has a natural resonance near 2700 Hz (i .e ., in the range of 2500 to 3000 Hz) on the order of 10 to 20 dB (Hawkins and Mueller, 1986 ; Libby,1986,1987 ; Dirks and Kincaid, 1987 ; Hawkins, 1987 ; Gallagher, 1989). These characteristics, however, have not been documented for ears of patients having TM perforations . TM perforations may alter acoustic and physical characteristics of the ear and produce an REUR that may differ from that of an ear with an intact TM . Typically, inserting a hearing aid into an ear reduces the natural gain observed in the REUR . Hearing aids are often selected to provide additional gain in the 2500 to 3000 Hz region to compensate for this insertion loss . If a TM perforation causes the insertion loss to occur at different frequencies than typically observed for the intact TM, and if the dispenser is unaware of this, then the compensation provided by the hearing aid may be at the wrong frequencies for a given patient. Therefore, a knowledge of alterations in the REUR produced by TM perforation is important because proportional compensations may be necessary or desirable in the frequency response of hearing aids fitted to these patients . Tympanic Membrane Perforations/Moryl et al The purpose of this study was to perform probe microphone measurements on a sample of patients having TM perforations to document the effects ofperforation size on the REUR (peak frequency and peak amplitude) . METHOD Patients Thirteen patients (six males and seven females) ranging from 17 to 88 (mean = 54) years of age were obtained from an otolaryngology practice over a 3-month period . All were diagnosed with TM perforations (10 unilateral and 3 bilateral) by an otolaryngologist (JRD) . The perforations varied in size . Two patients had tympanoplasties and were tested before and after surgical closure. One patient's perforation healed naturally and was also analyzed before and after closure. Stimulus and Instrumentation The speech-weighted composite signal (80 sinusoids from 100 to 8000 Hz spaced at 100 Hz intervals) provided by the Frye 6500 real ear probe microphone system was used as the stimulus for this study. This system consists of a reference microphone, a probe microphone coupled to a 0.95-mm outer diameter probe tube of soft, flexible silicone, and a 77-mm diameter soundfield loudspeaker located on an adjustable stand. Procedure Probe microphone measures were conducted in a room within an otolaryngology office . The patient was seated 18 inches from the soundfield loudspeaker. The loudspeaker was adjusted in a horizontal plane to the patient's ear at 45 degrees azimuth (re: the patient's nose). The reference microphone was attached to a Velcro headband placed just above the patient's pinna and facing forward. The probe tube was marked at 22 mm from the end of the probe tip. The probe tube was inserted 22 mm into the ear canal with the marked portion referenced to the opening ofthe meatus . Thus, assuming an average ear canal length of 24 mm (Zemplenyi et al ., 1985), the measures were made at a distance of about 2 mm from the TM . The insertion depth was verified by otoscopic inspection of the ear canal. This probe-tube position was used for all measures . Patients were instructed to remain still while the real ear measurements were obtained . When the reference and probe microphones were both in place, the probe tube was inserted into the patient's ear canal and the system was leveled (calibrated) using the composite signal . The REUR was then obtained for the ear having the TM perforation using the composite signal at 70 dB SPL. Each REUR was immediately stored and printed out in both graphic and numeric data forms. The probe tube was then removed from the patient's ear and reinserted to the same insertion depth in the same ear canal for a second measurement. All test-retest measures for each patient were repeatable within 2 dB of each other (except at 200 and 300 Hz) and were, therefore, considered reliable . For the 10 patients with one intact eardrum, an REUR was also obtained for that ear as a control using the same procedures as above. Thus, four REURs were collected for each patient. Both ears were tested for the three patients with bilateral TM perforations (i .e ., they did not have a control ear) . This resulted in a total of 16 perforations for analyses . Three of the patients (two after surgical closure, and one after his perforation healed naturally) were reevaluated using the same procedures as used for the first evaluation . RESULTS P eak frequency (in Hz) and peak amplitude (in dB gain) values for the ears having TM perforations and for the control (intact TM) ears are shown in Table 1. The table shows essentially no differences between the mean peak frequencies and mean peak dB gain of the perforated and control ears when the perforations are treated without regard to size . However, the table shows some individual variability among ears . The range for peak frequency was 1700 to 3700 Hz and that for dB gain was 8.7 to 25 .3 dB for the perforated ears . For the control ears, the range was somewhat smaller (2300 to 2900 Hz) for peak frequency, but greater for peak dB gain (9 .5 to 31 .9 dB). Not shown in the table, is the fact that several of the REURs for the perforated ears had two prominent peaks separated by a valley of at least 10 dB reduced gain (referred to here as a bimodal response). Figure 1 is an example of one such case . Note that, for this patient, the valley actually resulted in negative gain . This bimodal response was noted for 7 of the 16 ears having perforated TMs. Responses were only 61 Journal of the American Academy of Audiology/Volume 3, Number 1, January 1992 Table 1 Peak Frequency and dB Gain Points in the REURs for Each Ear Peak Frequency (Hz) Patient Perforation R L R L R L Mean = SD = Control 2700 3400 1900 2300 2400 2200 1700 2500 3000 3700 2600 2600 2300 2100 2100 3000 2600 2531 .25 535.06 2570 170 .29 2500 2300 2800 2900 2500 2500 2600 2500 2500 Peak Gain (dB) Perforation Control 22 .3 23 .1 24 .7 17 .6 24 .1 12 .4 25 .3 22 .4 22 .2 16 .0 9 .1 9 .8 8 .7 18 .5 25 .0 21 .9 18 .94 5 .98 23 .5 12 .9 23 .5 19 .6 18 .7 31 .9 9 .5 16 .7 16 .1 22 .3 Small Patient 1 2 3 4 5 6 7 8 9 10 11 12 13 Mean = 19 .47 6 .30 Note : 10 of the patients had one intact eardrum that served as a control ear ; three had bilateral perforations and responses were obtained for both right (R) and left (L) ears . analyzed up to 4000 Hz since data points above that cut-off are considered artifactual . The data were separated according to small (3 mm or less), medium (3 to 5 mm), and large (greater than 5 mm) TM perforations to determine whether size of the perforation produced differences in the REURs . The peak frequency and dB gain points for the REURs for the three perforation sizes are shown in Table 2. Aside from the lower values obtained for the medium sized perforations (note: only an n of 3), no apparent differences were observed among the mean values for size . However, seven of the ears with perforations exhibited bimodal REURs such as that noted earlier in Figure 1 : the REURs for all six ears having large perforations and one of the three ears having medium perforations . Figures 2, 3, and 4 show the REURs for three patients before and after closure of the perforations . Patient 6 (shown in Figure 2) had a small pinhole perforation, which healed naturally, and there was no large difference between the REURs for his ear with perforated and intact (control) TMs. After closure, the REUR for the ear with the healed TM and his control ear were exactly the same . The variation observed between this patient's pinhole perforation and his control TM was no greater than might be expected for two intact TMs of any individual . 62 Table 2 Peak Frequency and dB Gain Points in the REURs for Small, Medium, and Large Perforations Hz dB Gain 2700 3400 22 .3 23 .1 2400 24 .1 2500 3000 22 .4 22 .2 2100 2100 18 .5 21 .9 2600 22 .1 Large Medium Hz dB Gain 1900 2300 24 .7 17 .6 1700 25 .3 Hz dB Gain 2200 12 .4 3700 2600 2600 2300 16 .0 9 .1 9 .8 8 .7 3000 25 .0 2733 .3 13 .5 1966 .7 22 .5 Perforation sizes : small = 3 mm or less ; medium = 3 to 5 mm ; and large = greater than 5 mm . The other two patients (10 and 13), shown in Figures 3 and 4, respectively, had large perforations and received tympanoplasties. Before surgery, both patients' REURs demonstrated the bimodal configuration; after surgery they both exhibited only one prominent peak . After surgery, Patient 10's ear with the healed TM revealed a similar response to that with his intact TM . Recall that Patient 13 had bilateral TM perforations (one small and one large) . As noted earlier, his ear with the large perforation exhibited a bimodal REUR before surgery. After surgery, his REUR revealed only one peak characteristic of ears with intact TMs. dB --- 30 1 -- 20~---------------------------------10 .25 .5 1 2 4 KHz Figure 1 Example of a bimodal REUR for a patient having a large TM perforation. Note the two large peaks in the response separated by a valley of low gain. dtfji: li Iih 1 hi -ai11Ml Tympanic Membrane Perforations/Moryl et al dB 10 00 -10 -20 .25 (a) .5 1 2 4 KHz dB .25 (b) .5 1 2 4 KHz Figure 2 REURs for Patient 6 before (a) and after (b) closure of the TM perforation . DISCUSSION Ithough small perforations produced sinAgle-peaked REURs similar to those for ears with intact TMs, ears for one medium and all large perforations in this study exhibited bimodal REURs (see Fig. 1) . For the two large perforations in this study that were monitored through closure, the REURs for the ears with healed TMs were also similar to those with intact TMs. However, the responses observed for ears with one of the medium and all of the large perforations suggest that, if hearing aids were fitted to these ears, these perforations could create noticeable changes in the REIR. Specifically, the two peaks observed in the bimodal REURs for these patients would create insertion gain and loss at different frequencies from those typically noted for ears with intact TMs. Normally, a smooth insertion response is desirable in hearing aid fittings . Although a smooth response can also be obtained for ears .25 (b) .5 1 2 4 KHz Figure 3 REURs for Patient 10 before (a) and after (b) closure of the TM perforation having TMs with larger perforations, the additional peaks and valley in the bimodal response can present a challenge in hearing aid fittings . In our experience, we have not had difficulty fitting hearing aids to ears with small perforations . However, Figure 5a provides an example of a REUR from a patient with a large TM perforation showing a bimodal response having two prominent peaks (at about 800 and 2500 Hz) and a large valley (at about 1200 Hz) . Interestingly, the REIR in Figure 5b shows three corresponding large peaks at about 400, 1200, and 2500 Hz and two valleys (at about 800 and 2000 Hz). This patient complained of having loudness intolerance and speech discrimination problems with several behind-the-ear (BTE) hearing aids that were fitted to his loss . These complaints probably arose because the REIR was not smooth . We suspect that the patient tried to turn up the volume on the hearing aid to fill in the information that was missing from the valleys in the spectrum . In 63 Journal of the American Academy of Audiology/Volume 3, Number 1, January 1992 .25 (a) .25 (b) .5 .5 1 2 1 2 4 KHz .25 .5 1 2 4 KHz 4 KHz Figure 4 REURs for Patient 13 before (a) and after (b) closure of the TM perforation. doing so, excess gain was present in the spectrum where the peaks occurred, thus, causing discomfort and potential distortion of speech. The use of filters in the ear hook and in the earmold tubing helped somewhat . Here, it is important to have a hearing aid with a flexible response . Some digitally programmable hearing aids may allow the dispenser to program a response that closely approximates a chosen prescription fitting. This type of case demonstrates the importance of using probe microphone measures in hearing aid fittings, specifically when TM perforations are present. Electroacoustic test box or functional gain measures might fail to identify the peaks and the valley in the unaided response due to the perforation causing the patient's complaints . In summary, our results show that the ears havinglarge perforations had abnormal REURs. In fitting hearing aids, the increased cavity size produced by large TM perforations would likely require greater amounts of gain at some fre64 (a) (b) Figure 5 REUR of a patient with a large TM perforation (a). REIR for a hearing aid fit (b) to the ear in (a). The dark line is the target curve. These measures were taken with a Madsen IGO system rather than the Frye 6500 used in the other figures. quencies and less at others than would typically be needed for ears having intact TMs. This suggests that special compensations may be needed in fitting hearing aids to patients having large TM perforations . Although this conclusion is based on a small number of patients, all those having large TM perforations in this study exhibited similar bimodal REURs, which differed from REURs seen in ears with intact TMs and in those with small perforations . Acknowledgment. This research was supported by a University ofCalifornia Santa Barbara General Research Grant (8-587529-19900-7), a Graduate Student Humanities/Social Sciences Research Grant, and the Ear Foundation of Santa Barbara. The authors acknowledge David F. Henry and Maxine DiBartolomeo for their assistance in acquiring patients for this study. Special appreciation is expressed to H. Gustav Mueller, Lucille Beck, Dennis J. Arnst, Larry Revit, and Kimberly J. Danhauer for their valuable comments on this manuscript. Tympanic Membrane Perforations/Moryl et al REFERENCES Libby ER . (1986) . The shift toward real ear measurements. Hear Instr 37 : 6, 50 . Dirks DD, Kincaid GE . (1987) . Basic acoustic considerations of ear canal probe measurements . Ear Hear 8:6067S. Libby ER. (1987) . Real ear considerations in hearing aid selection. Hear Instr 38 : 14-16. Gallagher G. (1989) . Real-ear measurement . Hear J 42 : 11-17. Hawkins DB . (1987) . Clinical ear canal probe tube measurements . Ear Hear 8: 74-818 . Hawkins DB, Mueller HG . (1986) . Some variables affecting the accuracy of probe tube measurements . Hear Instr 37 : 8, 48 . Schweitzer HC, Sullivan RF, Beck LB, Cole WA . (1990) . Developing a consensus for "real ear" hearing instruments terms. Hear Instr 41 : 28, 46 . Zemplenyi J, Gilman S, Dirks D. (1985) . Optical method for measurement of ear canal length. JAcoust Soc Am 78 : 2146-2148.