Bj. Yates et Ia. Kerman, POST-SPACEFLIGHT ORTHOSTATIC INTOLERANCE, POSSIBLE RELATIONSHIP TO MICROGRAVITY-INDUCED PLASTICITY IN THE VESTIBULAR SYSTEM, Brain research reviews, 28(1-2), 1998, pp. 73-82
Even after short spaceflights, most astronauts experience at least som
e postflight reduction of orthostatic tolerance; this problem is sever
e in some subjects. The mechanisms leading to postflight orthostatic i
ntolerance are not well-established, but have traditionally been thoug
ht to include the following: changes in leg hemodynamics, alterations
in baroreceptor reflex gain, decreases in exercise tolerance and aerob
ic fitness, hypovolemia, and altered sensitivity of P-adrenergic recep
tors in the periphery. Recent studies have demonstrated that signals f
rom vestibular otolith organs play an important role in regulating blo
od pressure during changes in posture in a I-g environment. Because sp
aceflight results in plastic changes in the vestibular otolith organs
and in the processing of inputs from otolith receptors, it is possible
that another contributing factor to postflight orthostatic hypotensio
n is alterations in the gain of vestibular influences on cardiovascula
r control. Preliminary data support this hypothesis, although controll
ed studies will be required to determine the relationship between chan
ges in the vestibular system and orthostatic hypotension following exp
osure to microgravity. (C) 1998 Elsevier Science B.V. All rights reser
ved.