Morphology Of EABR In Cochlear Implant Users In Different Stimulation Mode

OBJECTIVE:In very young children with cochlear implant,objective measures play a vital role both before and after implantation.The most promising method is the registration of electrically evoked auditory hrainstem response(EABR).For effective use of EABRs it is important to determine the characteristic EABR changes due to the stimulation parameters.Our general objective was to investigate the impact of stimulation mode on morphology of EABR,and to compare the thresholds of EABR and electrically evoked compound action potential(ECAP) with the same pulse width of probe stimulation.METHOD:3 electrodes of 9 Nucleus 24M cochlear implant users,along the electrode array from base towards apex,were stimulated for ECAP and EABR registration.EABRs were recorded in MP1+2,MP1,MP2,BP+1,CG stimulation mode respectively.EABR waveⅢ,V appearace frequency,peak latency and amplitude were compared between 3 electrodes as well as between different stimulation modes.The relationship between EABR and ECAP thresholds were analysised with SPSS13.0.RESULTS:①ECAP threshold and EABR threshold of E3,E10,E20 was 197.88±12.21vs.200.9±16.4,195.23±9.97vs.197.8±11.8,182.03±12.08vs.185.1±20.8 respectively.The thresholds of E20 were lower than those of E30 and E10 with significant difference.②EABR wave V appearance frequency was 96.3%,94.4%,96.3%,14.8%,33.3% in MP1+2,MP1,MP2,BP+1,CG mode respectively.The appearance frequency in MP mode was higher than those in BP+1 and CG(P=0.010＜0.05,P=0.018＜0.05)③WaveⅢappearance frequency was 62.96%,59.26%,66.67%,14.81%,18.52% in MP1+2,MP1,MP2,BP+1,CG respectively.It was 22.22%,42.22%,68.89%in E3,E10,E20 respectively. ④The average waveⅢlatency was 2.06ms,and 2.11±0.46ms,2.07±0.86ms, 2.03±0.12ms in E3,E10,E20 respectively with no difference between 3 electrodes (F=0.719,P=0.503＞0.05).⑤In MP1+2 mode,waveⅤlatency of E3,E10,E20 was 4.09±0.16ms, 4.02±0.19ms,3.70±1.21ms,with shorter latency in apex(P=0.026,P=0.004).WaveⅤamplitude(μv)of E3,E10,E20 was 0.46±0.31,0.44±0.25,0.74±0.35.⑥EABR threshold(CL)was 193.6±12.5,190.3±13.0,189.3±12.2,207.5±44.4, 234.0±8.2 in MP1+2,MP1,MP2,BP+1,CG mode respectively,CG was significantly different with MP1,MP2,MP1+2(P=0.000＜0.01,P=0.000＜0.01,P=0.000＜0.01), with no difference between MP1,MP2,MP1+2(P=0.0987＞0.05,P=0.0915＞0.05, P=1.000＞0.05).⑦ECAP threshold was significantly correlated with EABR threshold(r=0.974,P＜0.01). A linear regression model was constructed as an equation:EABR=8.696+0.94×ECAP.A paired t-test indicated that there was no difference between them(t=5.377,df=25,P＞0.05).⑧Ipsilateral and contralateral recording were conducted simultaneously. Sometimes ipsilateral recorded waveforms had a better discrimination than contralateral counterparts.CONCLUSION:Monopolar stimulation mode exhibited advantage than bipolar and common ground mode in some respects.We recommend it as the first choice in EABR registration.What's more,ipsilateral and contralateral simultaneous recording is also recommended for a better identification of EABR waveforms.