The caloric vestibular nystagmus during short lasting microgravity.
In human subjects the caloric vestibular test was conducted during parabolic flight.  The ear irrigation was performed from 35 secs. till 5 secs. before the onset of microgravity.  Nystagmography covered a 10-minutes period, including three parabolic manoeuvres of the aircraft.  a.  The slow phase velocity (SPV) of the caloric nystagmus increased proportionally with the value of the g-force.  Introduction of microgravity induced an exponential decrease of the SPV decay.  b.  The nystagmus disappeared completely in microgravity, but SPV decay showed a specific time constant.  c.  The averaged time constant values of the caloric nystagmus SPV decay after sudden onset of microgravity and the averaged time constant of the SPV decay following a sudden stop after sustained rotation during 0-g appeared to be on the same level (10.2 s. and 10.6 s.).  d.  These two averaged time constant values obtained during short lasting microgravity proved to be on a lower level than those time constants (15.5 secs.; 15.9 secs.) found in ground-based conditions.  e.  Because of the similarities in the characteristics of both SPV decay's and their accompanying time constants, a common working mechanism of cupular stimulation is likely.  Most probably a fluid movement (or pressure) provokes a cupula deflexion followed by a cupula reflexion, either caused by a sudden stop after a sustained rotation or by a sudden onset of microgravity after g-load calorization.  The present results support the Barany convection theory with regard the endolymph stimulatory properties following the caloric test.
Oosterveld
W J
WJ
University of Amsterdam, Academisch Medisch Centrum, Meibergdreef, Amsterdam, The Netherlands.
de Jong
H A
HA
Kortschot
H W
HW
D000328:Adult; D002150:Caloric Tests; D004424:Ear Canal; D006801:Humans; D018471:Hypergravity; D008875:Middle Aged; D009760:Nystagmus, Physiologic / Q000502:physiology*; D016684:Prone Position; D012399:Rotation; D013026:Space Flight; D016683:Supine Position; D014893:Weightlessness