Interaction of the vestibular system and baroreflexes on sympathetic nerve activity in humans

Departments of Medicine and Cellular & Molecular Physiology, General Clinic Research Center, Pennsylvania State University College of Medicine, Hershey, Pennsylvania 17033 Muscle sympathetic nerve activity (MSNA) is altered by vestibular otolith stimulation. This study examined interactive effects of the vestibular system and baroreflexes on MSNA in humans. In study 1 , MSNA was measured during 4 min of lower body negative pressure (LBNP) at either 10 or 30 mmHg with subjects in prone posture. During the 3rd min of LBNP, subjects lowered their head over the end of a table (head-down rotation, HDR) to engage the otolith organs. The head was returned to baseline upright position during the 4th min. LBNP increased MSNA above baseline during both trials with greater increases during the 30-mmHg trial. HDR increased MSNA further during the 3rd min of LBNP at 10 and 30 mmHg ( 32% and 34%, respectively; P