title: The video head impulse test during post-rotatory nystagmus: physiology and clinical implications.
abstract: The aim of this study was to test the effects of a sustained nystagmus on the head impulse response of the vestibulo-ocular reflex (VOR) in healthy subjects. VOR gain (slow-phase eye velocity/head velocity) was measured using video head impulse test goggles. Acting as a surrogate for a spontaneous nystagmus (SN), a post-rotatory nystagmus (PRN) was elicited after a sustained, constant-velocity rotation, and then head impulses were applied. 'Raw' VOR gain, uncorrected for PRN, in healthy subjects in response to head impulses with peak velocities in the range of 150°/s-250°/s was significantly increased (as reflected in an increase in the slope of the gain versus head velocity relationship) after inducing PRN with slow phases of nystagmus of high intensity (>30°/s) in the same but not in the opposite direction as the slow-phase response induced by the head impulses. The values of VOR gain themselves, however, remained in the normal range with slow-phase velocities of PRN < 30°/s. Finally, quick phases of PRN were suppressed during the first 20-160 ms of a head impulse; the time frame of suppression depended on the direction of PRN but not on the duration of the head impulse. Our results in normal subjects suggest that VOR gains measured using head impulses may have to be corrected for any superimposed SN when the slow-phase velocity of nystagmus is relatively high and the peak velocity of the head movements is relatively low. The suppression of quick phases during head impulses may help to improve steady fixation during rapid head movements.
authors.affiliation: Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA. georgios.mantokoudis@insel.ch.|Department of Otorhinolaryngology, Head and Neck Surgery, Inselspital Bern, Freiburgstrasse, 3010, Bern, Switzerland. georgios.mantokoudis@insel.ch.
authors.forename: Georgios
authors.initials: G
authors.lastname: Mantokoudis
authors.affiliation: Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Ali S Saber
authors.initials: AS
authors.lastname: Tehrani
authors.affiliation: Nemours Biomedical Research, Alfred I. du Pont Hospital for Children, Wilmington, USA.
authors.forename: Li
authors.initials: L
authors.lastname: Xie
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, USA.|Department of Medical Engineering, University of Applied Sciences Upper Austria, Linz, Austria.
authors.forename: Karin
authors.initials: K
authors.lastname: Eibenberger
authors.affiliation: Department of Otolaryngology - Head and Neck Surgery, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Bernhard
authors.initials: B
authors.lastname: Eibenberger
authors.affiliation: Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: Dale
authors.initials: D
authors.lastname: Roberts
authors.affiliation: Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: David E
authors.initials: DE
authors.lastname: Newman-Toker
authors.affiliation: Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA.
authors.forename: David S
authors.initials: DS
authors.lastname: Zee
mesh_terms: D000328:Adult; D005260:Female; D064087:Head Impulse Test / Q000295:instrumentation / Q000379:methods*; D006801:Humans; D008297:Male; D009760:Nystagmus, Physiologic / Q000502:physiology*; D012027:Reflex, Vestibulo-Ocular / Q000502:physiology*; D012399:Rotation; D055815:Young Adult
keywords: Nystagmus; Vestibulo-ocular reflex (VOR); Video head impulse test; vHIT