On the regulation of arterial blood pressure by an intracranial baroreceptor mechanism.

Abstract

Maintaining sufficient cerebral blood flow is critical for brain function. There is evidence that one of the mechanisms that ensure adequate blood flow to the brain involves the regulation of systemic arterial blood pressure (ABP) by an intracranial baroreceptor mechanism sensitive to changes in brain perfusion. This experimental animal study aimed to provide a detailed characterization of this mechanism. In studies conducted in anaesthetized and conscious rats, cerebral perfusion was experimentally manipulated by applying precise, incremental physiological changes in intracranial pressure (ICP). The data show that (i) the intracranial baroreceptor triggers robust, non-habituating, proportional sympathetic and cardiovascular responses to acute and repeated ICP increases within the physiological range; (ii) there is a linear relationship between systemic ABP and ICP, as well as between sympathetic nerve activity and ICP; (iii) decreases in brain partial pressure of oxygen induced by physiological changes in ICP are negligible, making the brain tissue hypoxia an unlikely cause of the evoked sympathetic and cardiovascular responses; (iv) ABP responses induced by decreased cerebral perfusion are restrained by inputs from arterial baroreceptors, but are unaffected by renal afferent activity; (v) intracranial baroreceptor mechanism contributes to sympathoexcitatory responses induced by acute arterial hypotension; and (vi) activation of the intracranial baroreceptor mechanism resets the arterial baroreflex centrally, allowing regulation of systemic blood pressure at a higher level required to counteract reduced brain perfusion. These data support the hypothesis that cerebral perfusion is a major determinant of sympathetic activity and systemic arterial blood pressure, regulated by the intracranial baroreceptor mechanism. KEY POINTS: An intracranial baroreceptor mechanism contributes to the regulation of systemic arterial blood pressure to maintain cerebral blood flow. The intracranial baroreceptor mechanism triggers robust, non-habituating, proportional sympathetic and cardiovascular responses to physiological changes in brain perfusion. Arterial blood pressure increases induced by activation of the intracranial baroreceptor mechanism in response to reduced cerebral perfusion are restrained by inputs from arterial baroreceptors. The intracranial baroreceptor mechanism resets the arterial baroreflex centrally to regulate systemic blood pressure at a higher level required to counteract reduced brain perfusion.