[Vestibular control of the cardiovascular system].

Due to modern living conditions the human cardiovascular system is frequently exposed to rapid or/and prolonged changes in gravitational forces. These transients are very short compared to the timescale of the evolution causing substantial difficulties in adaptation. As it has been many times proven experimentally since the first observation in 1922, the vestibular system affects directly the regulation of the cardiovascular system. For example, bilateral transsection of the vestibular nerve of cats significantly disturbs the compensation of acute hypotension induced by lowering the animal's head. The results of human studies also indicate the existence of vestibulo-sympathetic reflexes. Vestibular excitation caused by caloric to other stimuli results in increased sympathetic efferent activity. Several groups or nuclei in the brain-stem (medial vestibular ncl., subretrofacial ncl., the lateral area of tegmentum) were confirmed to have important mediatory function in the central organization of the vestibulo-sympathetic reflex. However, the role of vestibular system in long-term adaptive responses of the vascular system of chronic changes in body position is not classified yet. Such a possible role is suggested by our experimental findings during the last decade. Electronmicroscopic examinations indicated that two-week long orthostatic load due to head-up tilting changes significantly and differently the innervation density of blood vessels in the extremities of rats. There also have been a significant amplification of acute myogenic response to intraluminar pressure-elevation in the saphenous vein. We suppose that adrenergic mechanisms under vestibular control are at least in part responsible for the regionally different adaptive changes including structural remodelling. Spectral analysis of the arterial blood pressure suggested that a two week-long orthostatic load can already alter the overall control of the cardiovascular system in rats.