抄録
Although the vestibular system plays a significant role in the arterial pressure (AP) response to gravitational changes, the physiological significance of this response remains unclear. Hypergravity causes orthostatic fluid shift from the intrathoracic compartment to the legs; this could result in reduced venous return and cardiac output, followed by decreased AP. Thus, the vestibular system-mediated pressor response may counteract the hypergravity-induced hypotension. In this regard, the vestibular system acts as a regulator of AP in order to prevent hypotension. On the other hand, microgravity causes a headward fluid shift that could result in increased venous return and cardiac output, followed by increased AP. Thus, if the vestibular system has a physiological significance in the control of AP during gravitational changes, it should induce a depressor response under microgravity conditions. Conversely, however, it induces a pressor response; i.e., the vestibular system induces a pressor response irrespective of the direction of the changes in gravity and the AP. These results suggest that the vestibular system-mediated pressor response is a type of stress response but not a purposeful response. This pressor response is, however, effective in preventing hypotension under hypergravity conditions and on postural change from recumbency to upright standing. In this presentation, I will review our resent data that supports a physiological significance of the vestibulo-cardiovascular reflex for preventing orthostatic hypotension. [J Physiol Sci. 2008;58 Suppl:S19]
