Vestibular system plays a significant role in arterial pressure control during head-up tilt in young subjects

We recently demonstrated that galvanic vestibular stimulation (GVS) obscured the vestibulo-cardiovascular reflex in rats during gravitational change. Here, we used GVS to examine the role of the vestibular-mediated arterial pressure (AP) control during a 60 degrees head-up tilt (HUT) in young and aged subjects (19-24 years old, 12 males and 3 females for young subjects, 63-91 years old, 5 males and 5 females for aged subjects). In young subjects, the AP did not change during posture transition from the supine position to HUT when GVS was not applied. When GVS was applied, AP immediately and significantly decreased by 17+/-2 mmHg upon HUT. When they were exposed to lower-body negative pressure (LBNP) in the supine position, the degree of footward fluid shift induced was the same as that induced by HUT. LBNP elicited only a footward fluid shift without alteration of vestibular input, while HUT elicited both. LBNP decreased the AP significantly, and the decrease was similar to that observed in the HUT with GVS. Thus, GVS modified the AP responses in young subjects during HUT but not during LBNP. In contrast, in aged subjects, the AP decreased during HUT regardless of whether GVS was applied. The vestibular system plays an important role in initial AP control during posture transition in young subjects. However, this function might be impaired in aged subjects.