Glycerol-induced fluid shifts attenuate the vestibulosympathetic reflex in humans.

摘要

The glycerol dehydration test (GDT) has been used to test for the presence of Meniere's disease and elicits acute alterations in vestibular reflexes in both normal and pathological states. Activation of the vestibulosympathetic reflex (VSR) increases muscle sympathetic nerve activity (MSNA) and peripheral vascular resistance. We hypothesized that the GDT would attenuate the VSR through fluid shifts of the inner ear. Sixteen male subjects (26 +/- 1 yr) were randomly assigned to be administered either glycerol mixed with cranberry juice (97 +/- 3 ml glycerol + equal portion of cranberry juice; n = 9) or a placebo control [water + cranberry juice (100 ml each); n = 7]. Subjects in both groups performed head-down rotation (HDR), which engages the VSR, before and after administration of either the glycerol or placebo. MSNA (microneurography), arterial blood pressure, and leg blood flow (venous occlusion plethysmography) were measured during HDR. Before glycerol administration, HDR significantly increased MSNA burst frequency (Delta8 +/- 1 bursts/min; P < 0.01) and total activity (Delta77 +/- 18%; P < 0.01) and decreased calf vascular conductance (-Delta20 +/- 3%; P < 0.01). However, HDR performed postadministration of glycerol resulted in an attenuated MSNA increase (Delta3 +/- 1 bursts/min, Delta22 +/- 3% total activity) and decrease in calf vascular conductance (-Delta7 +/- 4%). HDR significantly increased MSNA burst frequency (Delta5 +/- 1 and Delta5 +/- 2 bursts/min) and total activity (Delta58 +/- 13% and Delta52 +/- 18%) in the placebo group before and after placebo, respectively (P < 0.01). Likewise, decreases in calf vascular conductance during HDR before and after placebo were not different (-Delta13 +/- 4% and -Delta14 +/- 2%, respectively; P < 0.01). These results suggest that fluid shifts of the inner ear via glycerol dehydration attenuate the VSR. These data provide support that inner ear fluid dynamics can have a significant impact on blood pressure regulation via the VSR in humans.