Central Hemodynamic Response to Activation of the Vestibular Sympathetic Reflex with Head Down Rotation in Healthy Young Adults.

Abstract

The purpose of this study was to assess the effect of vestibular-sympathetic activation on estimated measures of central (aortic) hemodynamic load in young adults. Methods: 31 participants (n=14 female, 17 male) underwent radial tonometry and popliteal Doppler-ultrasound in the prone position with the head in a neutral position and during 10 minutes of head-down rotation (HDR) as a means of activating the vestibular sympathetic reflex. Subjective orthostatic intolerance was assessed utilizing a 10-item orthostatic hypotension questionnaire. Results: There was a reduction in brachial systolic BP during HDR (111±10 vs. 109±9 mmHg, p<0.05), but there was no change in aortic systolic BP (100±9 vs. 99±8 mmHg, p>0.05). Aortic augmentation index (-5±11 vs. -12±12%, p<0.05) and reservoir pressure (28±8 vs. 26±8mmHg, p<0.05) were reduced with a concomitant reduction in popliteal conductance (5.6±0.7 vs. 4.5±0.7 ml/min∙mmHg, p<0.05). Change in aortic systolic BP was associated with subjective orthostatic intolerance score (r = -0.39, p<0.05). Conclusions: Activation of the vestibular sympathetic reflex via HDR resulted in slight reductions in brachial BP concomitant with preservation of aortic BP. Despite peripheral vascular constriction during HDR, there was a reduction in pressure from wave reflections and reservoir pressure. Finally, there was an association between change in aortic systolic BP during HDR and orthostatic intolerance score suggesting that individuals that cannot defend against drops in aortic BP during vestibular sympathetic reflex activation may be more likely to experience higher subjective symptomatology of orthostatic intolerance.