Characteristics And Clinic Research Of Vestibular Evoked Myogenic Potential

Objective: Compare the characteristics of vestibular-evoked myogenic potential(VEMP) by defferent stimulator patterns in healty subjects of defferent genders, defferent ages, in defferent positions, to investigate the factor affecting the potentials and the amplitude of VEMP, and build up our parameter certerions. Investigated VEMP in benign paroxysmal positional vertigo (BPPV) , cerebellar and pontine ischemic stroke patients , to determine if this type of testing is valuable for diagnosising and estimating the severity of the diseases.Subjects and methods:Subjects: Sixty-five healthy subjects (34 male and 31 female), aged between 20 and 68 years, average 32.5 years, had not diseases of ears and vestibular system, were divided into three groups according to their age, group 1:20～40 years old,20 subjects(10 male and 10 female); group 2:21～40 years old, 24 volunteers(13 male and 11 female); group 3:41～60 years old,21 volunteers(11 male and 10 female). All subjects ,together with 25 patients with BPPV(19 females and 6 males, mean age 52.9±11.9 years (range 34–77 years), 12 patients with cerebellar ischemic stroke and 6 patients with pontine ischemic stroke were tested.Methods: Acoustic stimuli was given to one test ear and EMG was recorded from ipsilateral side.The electrode was attached on the middle half of the SCM on both sides symmetrically, a reference electrode was attached on the lateral end of the upper sternum and a ground electrode on the forehead.Head Elevation Method Every subject was in a supine position. a pillow was put under head to position the neck at about 30°elevation from horizontal. During recording, the investigator scrutinized the EMG monitor and the subject was instructed to maintain the head elevated in the pitch plane to active SCM contract at a relatively constant level (50 to 200μV).Head Rotation Method Every subject was in sitting position, rotated his/her head side away from one shoulder to activate the SCM. To ensure the SCM muscle activation, the subject was instructed to rotated his/her head until the investigator could see the contour of the SCM. The EMG activities were monitored during recording to maintain muscle activities at a relatively constant level(50 to 200μV).Click: Rarefaction clicks of 0.1 millisecond and 100 dB nHL duration were presented through a headphone.STB(short tone bursts)100 dB nHL; rise/fall time=1msec; plateau time=2 msec. The EMG signal was amplified 1000 times and band pass filtered (30 to 3000Hz) . The stimulation rate was 3 Hz and the analysis time for each stimulus was 100 msec. The responses to 200 stimuli were averaged and repeated twice. Two consecutive runs were performed to verify the reproducibility, and results were averaged for final response.Results:1. the characteristics of VEMP:1.1 No significant difference among latencies of the three groups(P>0.05), No gender-related difference was detected in the VEMP(P>0.05). There was a positive correlation between age and p13n23 amplitude of VEMP, negative correlation between age and p13n23 amplitude(γ=-0.581<0,-0.631<0 ,respectively), whereas no significant difference was observed between VEMPs of defferent side.1.2 In the elevation-rotation sequence, the response rate for the elevation method (100%) was significantly higher than the response rate for therotation method (70%). In contrast, no significant difference existed in the response rate between the two methods in the rotation-elevation sequence (85% versus 88%). Comparison of the response rates for the initial elevation (100%) and initial rotation methods (85%) revealed a significantly lower response rate for the initial rotation method. Mean latencies of the peaks p13 and n23 showed significant differences between the two methods when using the elevation-rotation sequence but no differences on the rotation-elevation sequence. Furthermore, the rotation method displayed significantly smaller amplitude than the elevation method when using the elevation-rotation sequence but no significant difference in amplitude between the two methods when applying rotation-elevation sequence。1.3 Click stimulation of 57 ears (98%) produced VEMPs (C-VEMPs), whereas 51 (88%) revealed positive short tone burst-evoked VEMPs (STB-VEMPs),exhibiting a significant difference (p < 0.05). Furthermore,C-VEMPs displayed shorter latency,longer interval and larger amplitude than STBVEMPs, with a significant difference (p < 0.05),respectively. 2. clinic research of VEMP:2.1 The VEMP from 30 affected ears of 25 BPPV patients revealed prolonged latencies in eight ears and decreased amplitude in one ear (nine abnormal ears; 30% of total). The rate of VEMP abnormalities in the affected BPPV ears was significantly higer than the corresponding rates in the control group. (P=0.012)2.2 VEMP responses were obtained in all patients with cerebellar and pontine ischemic stroke. At the group level, latencies and amplitudes, and the number of subjects with significantly deviant values did not differ between patients and controls. There were no latency or amplitude differences ipsilaterally or contralaterally to the lesion. At the individual level, there was no correlation between laterality of lesion and that of P13 or N23 abnormalities in patients with cerebellar strokes.Conclusion:1 the characteristics of VEMP:1.1 There is no relationship between the potentials in different ages and left-right differences of the VEMP .No gender-related difference was detected in the VEMPs. There was a negative correlation between age and the p13n23 amplitude of the VEMP. It is safe to evaluate the VEMP using the value of the non-affected side when assessing unilateral lesions. However, it may be necessary to take age into account in evaluating the VEMP when bilateral lesions are suspected.1.2 The head rotation method may serve as an alternative for eliciting VEMPs in those who cannot sustain SCM contraction by head elevation. However, the lower response rate with smaller amplitude prevents the use of the head rotation method as an initial screening test for VEMPs.1.3 C-VEMPs had a higher response rate,shorter latency, and larger amplitude than STBVEMPs.These findings suggest that click is superior to short tone burst to trigger VEMPs. Because C-VEMPs have a shorter p13 latency than STBVEMPs,the interpretation of prolonged latency differs in each stimulus condition.2. clinic research of VEMP:2.1 VEMP is a promising method for diagnosing and following patients with BPPV paroxysmal positional vertigo disease.2.2 Cerebellar strokes do not influence VEMPs. Moreover, despite previous reports,we were unable to find at a group level any statistically significant VEMP changes in patients with pontine strokes as compared with controls. Therefore, VEMPs do not appear a suitable tool for assessment of brainstem integrity in patients with posterior fossa strokes.