Ocular vestibular evoked myogenic potentials and motion sickness susceptibility.

BACKGROUND: A functional vestibular system is a prerequisite for motion sickness (MS) to occur. The otolithic organs (saccule and utricle) are currently considered to be important in the pathogenesis of MS. Recent investigations have demonstrated that the ocular vestibular evoked myogenic potentials (oVEMP) test is an objective evaluation of utricular function. To date, there is no functional guide that can serve as a diagnostic tool for individual susceptibility to MS. Therefore, we investigated the link between oVEMP and MS susceptibility. METHOD: The oVEMP test was performed on 31 MS susceptible and 23 nonsusceptible individuals. MS susceptibility was determined by self-declaration and by using the MS susceptibility questionnaire (MSSQ) and the Hamilton Anxiety Scale (HAS). RESULTS: Bilateral oVEMP responses were obtained in all subjects. HAS and MSSQ scores between the susceptible and nonsusceptible group were 18.27 +/- 5.23 vs. 2.34 +/- 1.21 and 28.12 +/- 6.53 vs. 2.34 +/- 1.45, respectively. Statistically significant differences in MSSQ and HAS scores were found between the MS susceptible and nonsusceptible groups. No differences were found between MS susceptible and nonsusceptible subjects in N10 and P15 wave latencies, N10-P15 interval, or peak-to-peak N10-P15 amplitude. However, there was a trend toward greater asymmetry ratio in the MS susceptible group than in the MS nonsusceptible group (18.55 +/- 10.24% vs. 13.25 +/- 9.47%), although statistical significance was not reached. DISCUSSION: It appears that no relation exists between oVEMP results and MS susceptibility. Nevertheless, the differences in the asymmetry ratios of oVEMP interpeak amplitude between the two groups revealed a trend toward marginal statistical significance.

Ocular vestibular-evoked myogenic potentials in healthy pilots and student pilots.

INTRODUCTION: Excellent vestibular function (including utricular function) is important for pilots to maintain correct spatial orientation during flight. Vestibular-evoked myogenic potential (VEMP) recorded from extraocular muscles, the so-called ocular VEMP (oVEMP), can be used to evaluate utricular function. However, oVEMP has not been applied to pilots because of lack of reliable normative data. Hence, this study is designed to establish preliminary normative data for oVEMP induced by air-conducted sound in pilots and student pilots. METHODS: There were 62 healthy student pilots (30 male and 32 age-matched female) and 31 healthy male fighter pilots who were recruited as study participants. During binaural air-conducted sound stimulation oVEMP was recorded bilaterally. The latencies of nI and pI, nI-pI interval, peak-to-peak nI-pI amplitude, and asymmetry ratio (AR) of oVEMP in all participants were collected. Meanwhile, the effects of gender and age on oVEMP were also investigated. RESULTS: The latencies of nI and pI, nI-pI interval, nI-pI interpeak amplitude, and AR of oVEMP in all participants were 10.35 +/- 0.66 ms, 15.18 +/- 1.07 ms, 4.75 +/- 0.99 ms, 6.75 +/- 4.13 microV, and 13.22 +/- 9.13%, respectively. No significant difference existed between male student pilots and male pilots in terms of oVEMP parameters. The only significant difference was the nI-pI amplitude between age-matched male and female student pilots: 6.96 +/- 3.85 microV for male student pilots and 5.47 +/- 3.10 microV for female student pilots. CONCLUSIONS: oVEMP should be interpreted with the AR rather than raw amplitude itself. Each institution should determine its own normal values.

[High Gy induced vestibular disorders in guinea pigs and its countermeasure by preconditioning].

OBJECTIVE: To explore if high G exposure can cause vestibular disorder in guinea pig and the possibility of preventing it by preconditioning with exposure to a low hypergravity environment before high G stimulus. METHOD: A total of 86 guinea pigs were divided into 4 groups: 1) 28 were treated with a stimulus of +10 Gy for 5 min (+10 Gy group); 2) 28 were preconditioned by exposure to 2 G environment for 8 d before the +10 Gy stimulus (preconditioning group); 3) 20 were exposed to 2 G environment for 8 d, but without +10 Gy stimulus (2 G group); the rest 10 served as control. Their vestibular related behaviour, including vestibulo-spinal reflex (VSR) and vestibulo-ocular reflex (VOR) such as head tremble, head deviation, spontaneous nystagmus, eye deviation, body tilt or looping, were observed directly, the choline acetyltransferase (ChAT) activity in VNC (vestibular nucleon complex) in brain stem were investigated by immunohistochemistry technique, and the relative gamma in each group were analysed. RESULT: The incidence of behavioral abnormalities (BA) in 10 Gy group (79%) is significantly higher than that in preconditioning group (50%). The relative gamma of staining showed that the content of ChAT in VNC of the +10 Gy group and preconditioning group were significantly higher than that in control group, but no difference was found between them in +10 Gy and preconditioning groups. CONCLUSION: High G exposure of +10 Gy for 5 min could cause vestibular disorders in guinea pigs, and preconditioning with pre-exposure to 2 G environment could alleviate it. ChAT activity changes in VNC may contribute to its mechanisms.

Inferior vestibular neuritis in a fighter pilot: a case report.

Spatial disorientation in airplane pilots is a leading factor in many fatal flying accidents. Spatial orientation is the product of integrative inputs from the proprioceptive, vestibular, and visual systems. One condition that can lead to sudden pilot incapacitation in flight is vestibular neuritis. Vestibular neuritis is commonly diagnosed by a finding of unilateral vestibular failure, such as a loss of caloric response. However, because caloric response testing reflects the function of only the superior part of the vestibular nerve, it cannot detect cases of neuritis in only the inferior part of the nerve. We describe the case of a Chinese naval command fighter pilot who exhibited symptoms suggestive of vestibular neuritis but whose caloric response test results were normal. Further testing showed a unilateral loss of vestibular evoked myogenic potentials (VEMPs). We believe that this pilot had pure inferior nerve vestibular neuritis. VEMP testing plays a major role in the diagnosis of inferior nerve vestibular neuritis in pilots. We also discuss this issue in terms of aeromedical concerns.

Horizontal canal benign paroxysmal positional vertigo in a fighter pilot.

Benign paroxysmal positional vertigo (BPPV) is the most common disorder of the peripheral vestibular system, characterized by intense, positional provoked vertigo. BPPV is thought to occur due to canalithiasis of the posterior semicircular canal. Recently, a new entity of BPPV, known as horizontal canal (HC)-BPPV, has been recognized. Although only 3 to 8% of BPPV is due to horizontal canal involvement, HC-BPPV is not rare. We present a case of a naval fighter pilot who had an incident of HC-BPPV on the ground. The pilot aeromedical evaluation and considerations are discussed.

[Audiological and vestibular evaluation of new coagulation factor C homology mutation carriers in a Chinese family].

OBJECTIVE: To analyze the clinical features of audiological and vestibular function in a Chinese family with late onset autosomal dominant nonsyndromic sensorineural hearing loss. METHODS: Comprehensive audiological and vestibular evaluation including pure tone audiometry, auditory brainstem response (ABR), electrocochleogram (EcochG), oculomotor testing, caloric tests, rotational testing, computerized dynamic posturography and vestibular evoked myogenic potentials (VEMP) were conducted to identify the hearing and vestibular impairment. RESULTS: All affected family members shared sensorineural hearing loss with full penetrance starting between the second and fifth decade of life as a high frequency loss which progresses to a severe to profound loss at the sixth to seventh decade. The extensive vestibular evaluation indicated that all affected members performed normally in computerized dynamic posturography and caloric testing. Impairment of the saccular otolith in all of six affected members was suggested by results of the VEMP test. The velocity step test generated abnormal time constants and sinusoidal oscillation test generated abnormal gains and phase in affected members indicated that horizontal canal vestibular hyporeflexia in history. All affected subjects examined in this family showed completely normal ocular motor responses in oculomotor testing, including smooth pursuit, optokinetic nystagmus, gaze and saccade. CONCLUSIONS: The predominant feature of the Chinese DFNA9 family was that all the affected subjects harboring COCH mutation in the vWFA2 domain didn't suffer the vestibular symptoms during their life time and comprehensive vestibular assessment revealed only subtle vestibular hypofunction in affected members of this family. There is a genotype-phenotype correlation in DFNA9.

[Characteristics of vestibular-ocular reflex in guinea pigs during eccentric sinusoidal rotation].

AIM: To observe the characteristics of vestibular-ocular reflex (VOR) of guinea pigs during eccentric sinusoidal rotation in different frequencies and radius, and compare them with that during axis rotation, obtain the parameters which reflect otolith functions, and provide experimental evidence for the establishment of otolith function test. METHODS: Guinea pigs were placed in axis of rotation and in an heading out eccentric position apart from rotation axis of 330 mm, 660 mm and 990 mm respectively, their VOR were recorded and compared under stimulus of sinusoidal rotations in the frequencies of 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6 Hz with the peak velocity of 60 degrees/s in each position. RESULTS: Both frequency and eccentric radius had significant effects on the VOR gain, it increased with the increase of frequencies and radius. The largest increase of the gain occurred at the frequencies of 0.3 and 0.4Hz, and no significant changes were observed above these frequencies. CONCLUSION: Enhancement ratio (ER) of VOR gain can reflect the extent of its increase with radius, and can be used as an index of otolith function, the stimulus profile of eccentric rotation at frequency of 0.4Hz and radius of 990mm is recommended as the stimulus profile for the otolith function test.

[Clinical significance of vibration-induced nystagmus in patients with unilateral peripheral vestibular disorders].

OBJECTIVE: To clarify the clinical significance of vibration-induced nystagmus (VIN) and to calculate the sensitivity and the specificity of the vibration test. METHODS: One hundred and twelve patients with unilateral peripheral vestibular disorders and 30 normal subjects were enrolled into this study. However, patients with spontaneous nystagmus were excluded. Vibratory stimuli (approximately 92Hz) were presented to the mastoids and the forehead. Patients and normal subjects also underwent head shaking testing and caloric testing. RESULTS: Of the 112 patients, 91 (81%) showed VIN which were mainly horizontal. VIN was more frequently evoked on the mastoids than on the forehead. In the majority of patients (76 cases), the direction of VIN was toward the healthy side, whereas patients with Meniere's disease (15 cases), showed nystagmus toward the affected side. None of 30 normal subjects showed VIN. Whereas, HSN was found in 70 (63%) patients and 9 (30%) in normal subjects. Of 112 patients, 10 showed a canal paresis (CP) value of caloric test less than 25% ,while 32 with a CP value between 25% and 40%, 48 with a CP value between 40% and 70%, and 22 with a CP value more than 70%. It is notable that with increasing canal paresis value on caloric testing, VIN was more likely to be evoked. CONCLUSIONS: VIN testing is a simple, non-invasive and well-tolerated clinical test that indicates unilateral peripheral vestibular dysfunction. VIN testing had greater sensitivity and the specificity than HSN testing in the diagnosis of unilateral peripheral vestibular disorders.