[V-C Reflex]
Plastic alteration of vestibulo-cardiovascular reflex and its countermeasure

RESEARCH OVERVIEW

• Orthostatic hypotension is one of the most common physical complications of spaceflight. One of the proposed mechanisms of this condition is the plastic alteration of the vestibulo-cardiovascular reflex, i.e., microgravity induces a plastic alteration of this reflex that may result in inadequate adjustment of the arterial pressure upon posture change. This possibility has to be examined in order to consider a prophylaxis and countermeasure of postflight orthostatic hypotension.
• The purpose of the research is to test the hypothesis that microgravity induces plastic alteration of the vestibulo-cardiovascular reflex, and vestibular-mediated pressor response is impaired after spaceflight, then orthostatic hypotension occurs. To examine this, contribution of the vestibulo-cardiovascular reflex in controlling AP upon head-up tilt (HUT) is examined before and after spaceflight.
• The vestibular system is known to be highly plastic; there are direct evidences of the altered vestibulo-ocular and vestibulo-spinal reflexes after spaceflight. However, a direct evidence of the altered vestibulo-cardiovascular reflex after spaceflight does not exist.

DESCRIPTION

The objectives of the research are to test the hypothesis that vestibular-mediated pressure response is impaired after spaceflight, then orthostatic hypotension occurs. To examine this, contribution of the vestibulo-cardiovascular reflex in controlling arterial pressure upon HUT is examined before and after spaceflight. For transient interruption of the vestibular-mediated pressure response, galvanic vestibular stimulation (GVS) is applied. The HUT is performed with and without GVS. The contribution of vestibulo-cardiovascular reflex to arterial pressure maintenance during HUT is estimated by comparing the arterial pressure responses between GVS-on and GVS-off conditions.

SPACE APPLICATIONS

This experiment has potential benefits to the promotion of space medicine as well as human space flight.

EARTH APPLICATIONS

This experiment has potential benefits to considering a prophylaxis and countermeasure of orthostatic hypotension in elderly subjects. Both spaceflight and elderly subjects whose daily activity is reduced, fluctuation of the vestibular input is low and both conditions are known to induce orthostatic hypotension. Thus, it is possible that the plastic alteration of the vestibulo-cardiovascular reflex is a relevant mechanism of orthostatic hypotension in these conditions.

OPERATIONAL REQUIREMENTS AND PROTOCOLS

Ten subjects are required. To accomplish this experiment, subjects are required to complete all 3 conditions (GVS-off, Strong GVS-on, Weak GVS-on), and at least 3 times of HUTs each condition for the data accuracy.