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.

Vestibular function in military pilots before and after 10 s at +9 Gz on a centrifuge.

BACKGROUND: Effects of high Gz acceleration can threaten flight safety through loss of consciousness or a lesser-known phenomenon, G-induced vestibular dysfunction (GIVD). There are reports of GIVD following high-G flight or centrifuge exposure. The aim of this study was to explore this problem under controlled conditions using a human centrifuge. METHODS: There were 11 pilots who were exposed to +9 Gz for 10 s. Measurements were made before and after G exposure to assess vestibular function, including spontaneous nystagmus, positioning nystagmus, optokinetic nystagmus, vestibular ocular reflex, vestibular-vision interaction, subjective vision vertical perception, and vestibular-evoked myogenic potentials. RESULTS: No significant change was found for vestibular function after the Gz exposure. CONCLUSION: It appears +9 Gz for 10 s does not produce GIVD. However, the possible effects of prolonged high G maneuvers in modern aircraft combined with head movements may warrant further study.

[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.

[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.

Perception of the cabin attitude changes in hypergravity.

BACKGROUND: The G-excess illusion is becoming increasingly recognized as a cause of aviation fatalities. Studies of this illusion have looked at perception of subjects' orientation by moving the head during hypergravity, but independent of the pilot's head movement with respect to aircraft. This illusion can also occur by aircraft motion, but this has not been studied extensively. OBJECTIVE: The aim of this study was to investigate the subject's perception of orientation to the simulator cab attitude changes at 1.6 G without making any head movement with respect to the cab, and assess the feasibility of simulating the G-excess illusion on the ground with a centrifuge-like spatial disorientation simulator. METHODS: The 1.6-G force field was provided by the gravitoinertial force (GIF) of the simulator when it made an off-center (planetary) rotation at a constant velocity of 130 degrees x s(-1). Eleven subjects' perceptions of orientation of the cab attitudes were collected respectively by their report before and after certain cab tilt, in a roll plane of 1.6 G. RESULTS: When the cab was tilted 20 degrees at 1.6 G, the subjects perceived the angle to be 48.6 +/- 39.4 degrees. CONCLUSION: Most subjects experienced an exaggerated sensation to the cab attitude changes in roll plane. G-excess illusion can be generated in a centrifuge-like device on the ground.