Cerebral blood flow regulation and cognitive function: a role of arterial baroreflex function

Fig. 1. Cognitive impairment and baroreflex. Mild cognitive impairment (MCI) attenuates baroreflex sensitivity (BR), and BR is further reduced in Alzheimer’s disease (AD), indicating that cognitive function may be associated with arterial baroreflex function [5]. The solid lines represent the derivation sample and the dashed lines represent the validation sample. BR obtained by the ARXAR model

Fig. 2. Paradox of CBF regulation and baroreflex. An acute increase in arterial blood pressure (ABP) causes cerebral vasodilation in the context of arterial baroreflex control of autonomic activity. By contrast, an acute increase in ABP causes cerebral vasoconstriction to protect the blood–brain barrier via cerebral autoregulation. On the other hand, an acute decrease in ABP causes cerebral vasoconstriction in the context of arterial baroreflex control of autonomic activity, and it causes cerebral vasodilation to washout carbon dioxide (CO2) in the brain via cerebrovascular CO2 reactivity

Fig. 3. The schematic of direct and indirect effects of barorefex on cerebral vasculature. Cerebral vasculature is affected by autonomic nervous system via baroreflex and other physiological mechanisms (direct effect, white). On the other hand, baroreflex control of autonomic function regulates systemic circulation which affects cerebral vasculature (indirect effect, black). Moreover, cerebral autoregulation (CA) and cerebrovascular CO2 reactivity regulates cerebral blood flow (CBF) (gray), and both CBF regulatory system are affected by autonomic function and systemic circulation

Fig. 4. The relationship between CBF and cardiac output (Q). Middle cerebral artery mean blood velocity (MCA Vmean) as an index of cerebral blood flow as well as forearm blood flow (FBF) was linearly related to the change in cardiac output (Q) at rest and during exercise [49]

Fig. 5. The role of cardiac baroreflex function for dynamic cerebral autoregulation. Thigh cuff release elicited a transient drop in arterial blood pressure and resultant tachycardia via the arterial baroreflex (a) and increase in cerebral vascular conductance (CVCi) via cerebral autoregulation (b). Vagal blockade (glycopyrrolate, GLY) attenuated this tachycardic response, and the rate of regulation (RoR) as an index of dynamic cerebral autoregulation was also inhibited in the vagal blockade condition compared to both control (CON) and β1-adrenergic blockade (metoprolol, MET) conditions, indicating that the baroreflex-induced tachycardia response plays an important role in dynamic cerebral blood flow regulation [51]

Fig. 6. The transition from aortic pressure (AoP) to CBF. Lower body negative pressure (LBNP) during orthostatic stress decreased cerebral blood flow velocity (CBFV) as well as AoP, and the gain of dynamic transition from pulsatile AoP to CBFV increased gradually during a graded LBNP. Moreover, this gain is associated with an arterial baroreflex-induced change in systemic vascular resistance (SVR). The closed circles or bars represent the steady-state component of hemodynamics, and the open circles or bars indicate a pulsatile component of hemodynamics [55]

Fig. 7. Effect of cute hypervolemia on CBF and peripheral vasculature via baroreflex. During parabolic flight, acute loading of baroreceptors drastically evokes a decrease in sympathetic nerve activity and consequently reduces peripheral vascular resistance, and the middle cerebral artery mean blood velocity (MCA Vmean) remains unchanged. This change in total vascular conductance (TVC) via the arterial baroreflex is associated with a change in the contribution of the cardiac output (CO) to MCA Vmean. Hyper hypergravity, micro microgravity [56]

Fig. 8. The relationship between baroreflex sensitivity and brain white matter neural fiber integrity. a Reduced baroreflex sensitivity is associated with lower fractional anisotropy (FA) and higher radial diffusivity (RD) in older adults, regardless of their cognitive status. FA provides a summary measure of axonal fiber tract integrity whereas RD reflects axonal demyelination. b BRS calculated during hypotension (top) showed a stronger relation with FA and RD than that during hypertension (bottom). Color bar shows the directionality of correlation and the magnitude of P value. The color in brain maps represent the statistically significant areas that are associated with BRS [6]. MCI mild cognitive impairment (color figure online)