title: Vestibulo-ocular reflex gain as a measure of vestibular function in guinea pigs while in a recompression chamber: apparatus design and effects of nitrogen narcosis.
abstract: There are several mechanisms whereby alteration of barometric pressure can produce vertigo in divers or aviators. Development of a reliable measure of vestibular function in an animal model is the first requirement for further study of these mechanisms. This report presents the development of a rotatory table device capable of evoking the vestibulo-ocular reflex (VOR) of a guinea pig while in a hyperbaric chamber. To assess the reproducibility of this response, eight animals were monitored by electronystagmography during rotations at three table velocities (62.4, 83.3, and 100 degrees/s). Two test sessions were performed on each animal with a 6-hour interval between sessions. The VOR gain was calculated by dividing the average peak velocity of the slow phase component of the nystagmus by the peak stimulus velocity. At least eight observations per test speed were averaged; calibration of eye movement was performed prior to each session by forced ocular abduction. Multifactorial analysis of variance revealed no significant differences (p > .05) between the differing rotation speeds nor between test sessions for individual animals. However, there was a significant difference in VOR gain between animals (p < .002). The VOR gain was then measured, using the same techniques, in another group of seven animals before, during, and after an air dive to the equivalent of 200 feet of seawater (7.06 atmospheres absolute) to assess the effects of nitrogen narcosis. Pre- and post-dive VOR gains were significantly greater than those measured at depth (p < .05). These results are consistent with the slow processing model of nitrogen narcosis and the controversial theory that central nervous system depressants decrease the VOR gain. The results also demonstrate the ability of this inexpensive apparatus to provide a sensitive measure of pressure-induced changes of vestibular function in guinea pigs.
authors.affiliation: Department of Otolaryngology--Head and Neck Surgery, National Naval Medical Command, Bethesda, MD 20889, USA.
authors.forename: D M
authors.initials: DM
authors.lastname: Stevens
authors.forename: A J
authors.initials: AJ
authors.lastname: Dutka
authors.forename: J E
authors.initials: JE
authors.lastname: Snyder
mesh_terms: D000704:Analysis of Variance; D000818:Animals; D001273:Atmosphere Exposure Chambers; D003664:Decompression / Q000295:instrumentation; D004867:Equipment Design; D006168:Guinea Pigs; D008297:Male; D009569:Nitric Oxide / Q000008:administration & dosage* / Q000494:pharmacology; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D014724:Vestibular Function Tests / Q000295:instrumentation* / Q000379:methods; D014722:Vestibule, Labyrinth / Q000502:physiology*
chemical_list: D009569:Nitric Oxide