effect of tympanic membrane perforation on real-ear to coupler difference acoustic transform function

Real-Ear-to Coupler Difference [RECD] is the difference in decibels, as a function of frequency, between the SPL at a specified measurement point in the ear canal and the SPL in a 2cc coupler, for a specified input signal. We investigated the effects of tympanic membrane perforation on the RECD. RECD was obtained using an insertion gain analyzer for 24 adult patients with dry tympanic membrane perforation [group 1] [31 ears] and 20 healthy adult control subjects [group 2] [40 ears]. Cases showed moderate conductive hearing loss in their mean hearing threshold level. There was no statistically significant difference between both anterior and posterior locations as regards the degree of hearing loss or as regards the RECD. There was a statistically significant difference of RECD at frequencies 250Hz, 500Hz and 750Hz, between both groups. The RECD was 3 to 6dB lower in group 1 than in group 2. There was a statistically significant difference on comparing RECD at frequencies 250Hz, 500Hz, 750Hz and l000Hz in right ears, and at frequencies: 250Hz and 500Hz and 750Hz in the left ears of both groups. In group 1, there was no statistically significant difference of RECD values at different frequencies between right and left sided perforations and there was no statistically significant difference of RECD values at different frequencies between both genders except at 1500Hz. There was no statistically significant correlation between the RECD and the age of the patients or their air-bone gap. RECD in patients with tympanic membrane perforation is lower than normal at frequencies [250Hz-750Hz]. We recommend that this discrepancy should be compensated for if average normal RECD are used in the preselection of target and gain to avoid under-amplification at lower frequencies. However, the large inter-subject variation strongly suggests the need for individual RECD measurements whenever possible in fitting aids for patients having tympanic membrane perforations

Comparison of auditory steady state response among normal hearers and patients with different degrees of sensorineural hearing loss

50 adult subjects [100 ears], with a mean age of 33.47 years +/- 10.53 ranging from 18 to 70 years, were enrolled in this study. Ears were divided into 7 groups according to the degree of hearing obtained by pure tone audiometry [PTA]. Auditory steady state response [ASSR] was done for all groups by means of the MASTER biologic. To study the ASSR among normal individuals and patients with different degrees of sensorineural hearing loss [SNHL] and find out the ASSR and behavioural threshold difference in these groups. There was no statistically significant difference among the groups as regards age or gender [p>0.05]. There was a statistically significant difference [p<0.05] among the groups as regards the mean PTA-ASSR hearing threshold difference at all frequencies. The difference decreased as the degree of hearing loss increased [the mean hearing threshold level obtained by ASSR approaches that obtained by PTA] at severer degrees of SNHL [at groups 5, 6 and 7]. The behavioural thresholds obtained by PTA and physiologic thresholds obtained by ASSR were highly correlated. The relationships were described by the following equations: Average PTA = -25.76 + [1.11 x Average ASSR] and according to the frequencies, at 500 Hz: PTA= -22.77 + [1.02xASSR]; at 1000 Hz: PTA= -21.30 + [1.03xASSR]; at 2000 Hz: PTA= -14.58 + [0.99xASSR] and at 4000 Hz: PTA= -14.50 + [0.98xASSR]. ASSR threshold does not reflect the PTA threshold reliably in normal hearers and in milder degrees of SNHL. And ASSR threshold reflects PTA threshold more reliably at severer degrees of SNHL especially at mid frequencies [1000 and 2000 Hz]. So we recommend using ASSR as an additional objective method in estimating the behavioural threshold at moderately severe, severe and profound SNHL with attention in estimating the hearing threshold by ASSR in normal hearing and in slight, mild and moderate degrees of SNHL