| In clinical forensic medicine expertise, the standard for the degree of the auditory loss by the language frequency for the average value of 0.5kHz, lkHz and 2kHz. The auditory brainstem response (ABR) has been developed as the most widely application for the objective assessment. However, the ABR evoked by clicks has some limitations, as it evaluates hearing sensitivity only at higher frequencies above 2000Hz but can not be sensitive for the thresholds for lower and middle frequencies.These studies for objective method of hearing thresholds were important questions in clinical forensic medicine. At present,in our country, there is little study for transience MLR on hearing thresholds. In the forensic medicine, there were no related study report about transience middle latency response (MLR) evoked by tone brust on hearing thresholds.In this study, the subjects for 59 volunteers,40(80 ears) and 19(28 deaf ears) were included. We tested for the pure tone threshold audiometry(PTA), transience MLR,40Hz auditory evoked response potential evoked by tone trust, then thested auditory brain-stem potentials evoked by click. Comparing and analysising their frequency-specific stimuli, sensitive, and influence factors in the test, the aim is toevaluate their their application value in the forensic medicine.Subjects and methodsThe subjects for 59 volunteers , forty normal hearing undergraduate (80 ears) volunteers at China Medical University and 19 deaf volunteers (28 ears) participated in our experiment. Forty normal hearing undergraduate (80 ears) volunteers had normal hearing sensitivity at all frequencies from 500 to 8000 Hz (＜25dBHL). For the deaf group, the following is the diagnosis standard of the deaf, deaf is from private prosecution, the test of ABR is abnormal, hearing thresholds in all frequencies from 500 to 8000 Hz testd by pure tone threshold audiometry, to affirm them by the the Same Frequency Tone Masking Test.The subjects reclined comfortably on an examination couch in an audiometric room. After pure tone auditory thresholds had been obtained at 1000, 500, 2000 and 4000Hz, 40Hz AERP and transience MLR thresholds to tone burst, ABR by click. Tone pips were determined. The response to tone burst was recorded with a Nicolet Compact Four Electrodiagnostic System. The earphone (TDH-39P) produced tone pips. The electrodes were placed at the vertex (positive input), ipsilateral mastoid (negative input) and forehead (ground). Individual impedances were less than 5kΩand inter-electrode impedance was below 3kΩ. The subjects reclined comfortably on an examination couch in an audiometric room. AEP to tone pips testing was started at 80dB nHL for normal group, 110dBnHL for deaf group. The stimulus level was decreased with 10dBnHL until no AEP waveforms could be detected. The responses were written out on a X-Y plotter at last.Results1. For the normal group, when the transience MLR evoked by tone trust, Three positive waves and three nagative waves were obtained from all the subjects for each frequency, So we called them NO,P0,Na,Pa,Nb,Pb.2. As the frequency of tone pips increases, the latency of each transience MLR waves decreases. The transience MLR and 40 Hz AERP threshold can be influenced by sleep.3. Mean differences and standard deviations for PTA at 500, 1000, 2000 and 4000Hz were 14.13±4.48 dB,9.314±4.39 dB,6.444±5.11 dB,7.56±7.20 dB, respectively. Mean differences and standard deviations for the transience MLR thresholds to trust tone were 20.31±4.99 dB,15.81±4.61 dB,18.06±6.33 dB,19.63±7.24 dB, respectively. Mean differences and standard deviations for 40Hz AERP thresholds to trust tone were 19.50±5.00dB,15.68±5.08 dB,15.56±6.00 dB,19.68±8.28 dB, respectively. Mean differences and standard deviations for ABR is 22.31±5.03 dB. 4. Mean differences and standard deviations between the transience MLR thresholds to trust tone and PTA were 6.19±2.14dB,6.50±2.57 dB,11.63±9.80 dB,12.06±3.25 dB, respectively. Mean differences and standard deviations between 40Hz AERP thresholds to trust tone and PTA were 5.38±2.61 dB,6.384±3.08 dB,9.13±3.35 dB,12.13±3.35 dB,respectively. At 500, 1000, 2000 and 4000Hz, the regression equation between transience MLR thresholds and PTA is Y=0.81x-2.36, Y=0.79x-3.17, Y=0.63x-4.99, Y=0.90x-10.11, respectively, the regression equation between 40Hz AERP thresholds and PTA is Y=0.77x-0.80, Y=0.68x-1.37, Y=0.71x-4.54, Y=0.80x-8.21, respectively.5. Mean differences and standard deviations between MLR thresholds to trust tone were 6.79±2.43dB, 6.60±2.74 dB, 11.07±3.15 dB, 11.78±2.43 dB, respectively. Mean differences and standard deviations between 40Hz AERP thresholds to trust tone were 5.00±2.36 dB, 5.89±4.52 dB, 8.75±3.23 dB, 12.68±3.96 dB, respectively. For the normal and deaf groups,There were no significant deviation for the mean differences of the differences between MLR,40Hz AERP thresholds to tone trust and pure tone thresholds(P＞0.05). For the pure auditory curve chart, there were exceedingly significant deviation at the high frequency losing group and the low frequency losing group.Conclusion1. For the normal group, when the transience MLR evoked by tone trust, three positive waves and three nagative waves were obtained from all the subjects for each frequency. The latency of the component was between 7 and 65 ms, so we called them NO,P0,Na,Pa,Nb,Pb. The transience MLR threshold can be influenced by sleep. 40Hz AERP is composed by some fusion waves.2. ABR can not be sensitive for middle and low frequency, but be very sensitive for high frequency, it can be used to evaluate hearing threshold in high frequency. MLR threshold is near the subject tone threshold, especially 40Hz AERP, so they can be used to evaluate hearing threshold in middle or low frequency. MLR threshold can be influenced by sleep, especially the transience MLR.3. As the frequency of tone pips increases, the latency of each transience MLR waves decreases. By the same intensity of sound, the latency diversify characteristic of different frequency transience MLR, We can inference the deaf low frequency hearing lose or high frequency hearing lose.4. In the forensic medicine expertise, only when suitable bandpass filtering, superposition number of times and eligible tone were selected, can we obtain stabile MLR waves, it can be used for hearing threshold evaluation in forensic medicine expertise. |
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