Subsensory galvanic vestibular stimulation augments arterial pressure control upon head-up tilt in human subjects.

The vestibular system plays an important role in control of arterial pressure (AP) upon head-up tilt (HUT). To examine this role in human subjects, we previously compared changes in AP with and without high-amplitude galvanic vestibular stimulation (GVS), which is considered to obscure vestibular input. In contrast, regarding sensory function in skin and muscle, it has been documented that low-amplitude electrical stimulation improves both sensitivity and response. In the present study, we examined whether GVS of smaller amplitude improves AP control upon HUT. GVS was applied at the amplitude of the somatosensory threshold (0.3-0.8 mA), 0.1 mA over the threshold, and 0.1 and 0.2 mA below the threshold during HUT. AP decreased at the onset of HUT compared with that in the supine position in 15 of 25 subjects without GVS (-12±2 mmHg), but applying GVS at 0.1 mA below the somatosensory threshold diminished the decrease (0.3±0.7 mmHg). The APs of another 10 subjects were maintained or decreased by less than 5 mmHg without GVS at the onset of HUT (4±2 mmHg), but applying GVS at the amplitude of 0.1 mA below the somatosensory threshold further increased the AP (12±2 mmHg). GVS at the other amplitudes did not result in AP changes in either group. Thus, subsensory weak GVS enhances AP control at the onset of HUT.