Study On Long Latency Auditory Evoked Potentials And Their Application Value In The Forensic Medicine

IntroductionIn forensic medicine expertise practice,the standard for the degree of the auditory loss is generally measured by pure tone average air conduction audibility threshold of a few decibels of the speech frequency,including the average value of 0.5 kHz,1 kHz and 2 kHz.At present,Auditory Brainstem Potentials(ABR) evoked by click is the most widely used technically mature and objective detection method among all kinds of Auditory Evoked Potentials(AEP) detection methods.However,since ABR evoked by click mostly presents high frequency audibility threshold situations above 2kHz,which turns out worse in presentation of middle and low frequency audibility threshold situation,and ABR are frequency-specific in detecting functional state of auditory pathway in and below brain stem.Therefore,it is not exact method for detecting the actual situation of auditory loss of the subject's different frequency that evaluate audibility threshold of speech frequency only by ABR.According to the relations between AEP evoked by a frequency-specific tone pip and subjective audibility threshold of different frequency,the researchers find ALR which is evoked by a frequency-specific tone pip can reflect the functional state of the whole auditory pathway.But,at present,it is rarely reported about how to use ALR to evaluate auditory loss at home and aboard,especially in the application of forensic medicine expertise practice.This research tested 45(78ears) subjects.All subjects are tested including items of pure tone audibility threshold,tone pip audibility threshold and ALR respond threshold evoked by tone pip,and then research on the interrelation and influential factor among the three,aiming at analyzing and evaluating the forensic medicine application values of ALR.Subjects and methodsSubjects among all the 45(78ears) subjects,auditory normal group includes 20(40 ears) are college students,One of the men and women 10,the average age is 25.9-year-old and their auditory normality was proven by pure tone air conduction auditory threshold less than 25dB.Deaf group includes 17(22 deaf ears) subjects,among them,there are ten males,five two-deaf people(10 deaf ears),twelve single deaf people,six Conductive deafness People,eleven people of neurosensory deafness.Deaf affirmed by private affirmation,ABR test results abnormality,and the auditory conditions of different frequencies were examined through several times of pure tone air conduction auditory threshold test.The extent of hearing loss rangs from 35dB～90dB expected by ABR.Contusion and laceration of brain group 8(16ears) subjects;among them,there are six males,two females,the age range from 19～55-year-old,diagnosis of contusion and laceration were confirmed by cephalic CT or MRI films,pure tone air conduction auditory threshold of each frequency was less than 25dB.Methodssubjects were tested in a acoustic chamber,followed by pure tone audibility threshold of four frequencies,that is 0.5 kHz,1 kHz,2 kHz,and 4 kHz,tone pip audibility threshold and ALR respond threshold evoked by tone pip.When testing pure tone audibility threshold,we record the results by FONMXFA—12 type pure tone audiometer,parameters seted as following:frequency range:125Hz～8000Hz, minimum output:—10 dB,maximum output:110 dB.When testing tone pip audibility threshold and ALR respond threshold evoked by tone pip,we use Nicolet Compact Four(US product) multifunctional electro physiolograph as recording system,sound output by TDH—39P type earphone.Silver disk electrode recorded the tone pip ALR, active electrode placed in the central middle point(Cz),reference electrode placed in the medial of ear lobe at the same side(A1,A2),ground electrode placed in the midpoint of frontal pole(Fpz).Electrode electric resistance is less than 5kΩ; interelectrode electric resistance difference is less than 3kΩ.When recording ALR,the beginning scale was 80dB in auditory normal group and 110 dB in deaf group, decreasing by 10dB each,then 5dB when close to Response threshold until the disappearance of respond wave,then test again and record.Permit the subjects to rest for 5～10 minutes after testing ALR for Specific frequency.,finally recorded by X—Y recorder.Results1.The typical ALR includes P1,N1,P2,N2 and P3 wave,and among them the amplitude of N1,P2 wave is the most obvious and the occurrence rate is 100%.The minimum sound intensity will be determined as ALR respond threshold evoked by tone pip which can evoke ALR N1,P2 wave.2.The ALR respond threshold evoked by tone pip and pure tone audibility threshold of the auditory normal group,the mean values and standard deviations for 0.5 kHz,1 kHz,2 kHz and 4 kHz are 7.33±3.12dB,8.11±2.62dB,7.22±2.50dB,9.19±2.85dB respectively.The mean values and standard deviations of tone pip audibility threshold and the pure tone audibility threshold are 3.48±2.17dB,4.33±2.36dB,4.07±1.78dB,3.96±2.21dB respectively;The mean values and standard deviations of ALR respond threshold evoked by tone pip and the pure tone audibility threshold are 3.85±2.27dB,3.78±1.83dB,3.15±2.14dB,5.22±2.04dB respectively.3.In the four frequencies of 0.5 kHz,1 kHz,2 kHz and 4 kHz,regression equations of ALR respond threshold evoked by tone pip and subjective hearing thresholds are Y=0.87x-4.18,Y=0.91x-6.49,Y=0.6x-1.21,Y=0.99x-9.03 respectively.T-test shows:P＜0.01.4.In the four frequencies of 0.5 kHz,1 kHz,2 kHz and 4 kHz,the ALR respond threshold evoked by tone pip and pure tone audibility threshold of the deaf group,the mean values and standard deviations were 7.00±3.08dB,8.14±2.57dB,7.37±2.79dB,9.45±3.02dB respectively.The mean values and standard deviations of tone pip audibility threshold and the pure tone audibility threshold are 3.56±2.58dB,4.24±2.46dB,4.18±2.01dB,4.03±2.33dB respectively;The mean values and standard deviations of ALR respond threshold evoked by tone pip and the pure tone audibility threshold are 4.01±2.34dB,3.88±1.97dB,3.05±2.17dB,5.27±2.39dB respectively. T-test shows no significant difference(P＞0.05) between the difference of the ALR respond threshold evoked by tone pip and the pure tone audibility threshold both in deaf group and auditory normal group.5.In the four frequencies of 0.5 kHz,1 kHz,2 kHz and 4 kHz,the mean values and standard deviations of the differences between ALR respond threshold evoked by tone pip and pure tone audibility threshold of the contusion and laceration of brain group are 7.21±3.21dB,8.21±2.31dB,7.02±2.91dB,9.53±3.27dB respectively.The mean values and standard deviations of the differences between tone pip audibility threshold and pure tone audibility threshold are 3.38±2.76dB,4.11±2.27dB,4.02±2.14dB,4.01±2.43dB respectively.The mean values and standard deviations of the differences between ALR respond threshold evoked by tone pip and tone pip audibility threshold are 3.92±2.12dB,3.96±2.07dB,3.11±2.18dB,5.47±2.22dB respectively.T-test of the differences between ALR respond threshold evoked by tone pip and pure tone audibility threshold both in contusion and laceration of brain group and the auditory normal group proves no significant difference between them(P＞0.05).when T-test of the latencies of ALR N1,P2 wave between contusion and laceration of brain group and the auditory normal group were finishde.There were no significant difference found in N1,P2 wave.(P＞0.05)6.With the increased intensity of the sound stimulus,the latencys of ALR N1,P2 wave gradually reduce,the amplitudes gradually increase.7.In the four frequencies of 0.5 kHz,1 kHz,2 kHz and 4 kHz,86.25%of the differences between ALR respond threshold and pure tone audibility threshold are less than 10dB.So when predicting pure tone audibility threshold by applying ALR respond threshold,conservative estimation should be deducted(0～10dB) from ALR respond threshold,that is the prior estimate circumscription of pure tone audibility threshold.Conclusion1.The typical ALR includes P1,N1,P2,N2 and P3 wave,and among them the amplitude of N1,P2 wave is the most obvious and the occurrence rate is 100%.N1,P2 wave response threshold,latency and wave amplitude is the main observed ALR.2.With the increased intensity of the sound stimulus,the latencys of ALR N1,P2 wave gradually decurtate,the amplitudes gradually increase.3.Test results showed that under strong say in the same,1000Hz and 2000Hz smaller latency,larger amplitude.4.ALR has a specific frequency,close to the subjective auditory threshold,the response of the auditory pathway to the functional status.Different types of deafness and brain contusion(no hearing impairment) subjects can be assessed.5.ALR belongs to the cortexas a result of response,therefore,in order to get a better ALR waveforms,subjects in the tests must be kept awake.