Consequences of removal of vestibular inputs on patterning of blood flow to the limbs during postural alterations in conscious felines

Abstract

Previous studies showed that removal of vestibular inputs results in lability in blood pressure during postural alterations. In addition, stimulation of vestibular afferents produces reciprocal changes in sympathetic outflow to and perfusion of the forelimb and hindlimb. These findings led to the hypothesis that activation of the vestibular system during postural alterations elicits patterned changes in limb blood flow that serve to maintain orthostatic tolerance. The present study tested this hypothesis by recording flow through the brachial and femoral arteries of conscious felines that were tilted head-up by up to 60°, before and after transection of the VIIIth cranial nerves. Blood pressure was also recorded so that vascular resistance of the forelimb (FVR) and hindlimb (HVR) could be calculated. In vestibular-intact cats, 60° head-up tilts were accompanied by increases in HVR of ~15%, and a ~12% increase in FVR. After VIIIth nerve transections, the posturally-related increases in HVR were significantly diminished, although there was only a small attenuation of the FVR response. These data support the hypothesis that vestibular signals elicit patterned changes in the activity of muscle vasoconstrictor efferents that act to stabilize blood pressure during postural alterations.