Inter-individual Relationships between Sympathetic Arterial Baroreflex Function and Cerebral Perfusion Control in Healthy Males.

Trevor Witter,Terry O'Donnell,Bridget Walker,Mary Berry,Chloe E Taylor,Yu-Chieh Tzeng,Jessica Kusel

doi:10.3389/fnins.2017.00457

Trevor Witter, Terry O'Donnell + Show 5 more

Open Access

https://doi.org/10.3389/fnins.2017.00457

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Abstract

Maintenance of adequate cerebral perfusion during normal physiological challenges requires integration between cerebral blood flow (CBF) and systemic blood pressure control mechanisms. Previous studies have shown that cardiac baroreflex sensitivity (BRS) is inversely related to some measures of cerebral autoregulation. However, interactions between the sympathetic arterial baroreflex and cerebral perfusion control mechanisms have not been explored. To determine the nature and magnitude of these interactions we measured R–R interval, blood pressure, CBF velocity, and muscle sympathetic nerve activity (MSNA) in 11 healthy young males. Sympathetic BRS was estimated using modified Oxford method as the relationship between beat-to-beat diastolic blood pressure (DBP) and MSNA. Integrated control of CBF was quantified using transfer function analysis (TFA) metrics derived during rest and Tieck's autoregulatory index following bilateral thigh cuff deflation. Sympathetic BRS during modified Oxford trials was significantly related to autoregulatory index (r = 0.64, p = 0.03). Sympathetic BRS during spontaneous baseline was significantly related to transfer function gain (r = −0.74, p = 0.01). A more negative value for sympathetic BRS indicates more effective arterial baroreflex regulation, and a lower transfer function gain reflects greater cerebral autoregulation. Therefore, these findings indicate that males with attenuated CBF regulation have greater sympathetic BRS (and vice versa), consistent with compensatory interactions between blood pressure and cerebral perfusion control mechanisms.

Highlights

The dynamic regulation of cerebral blood flow (CBF) is an integrative process that involves multiple homeostatic mechanisms (Ogoh et al, 2008)
In individuals prone to syncope head-up tilt is associated with impaired cerebral autoregulation and an inability to activate the cardiac baroreflex compared to individuals not prone to syncope (Bari et al, 2017)
It has been found that markers of blood pressure variability were positively related to metrics of Cerebral Autoregulation autoregulation (CA), and inversely related to cardiac baroreflex sensitivity (BRS) (Tzeng et al, 2010). These findings indicate that individuals with low cardiac BRS and high blood pressure variability are not necessarily deficient in their integrated capacity to control CBF because they had high levels of CA

Summary

Introduction

The dynamic regulation of cerebral blood flow (CBF) is an integrative process that involves multiple homeostatic mechanisms (Ogoh et al, 2008). Sympathetic Baroreflex Sensitivity and Cerebral Autoregulation autoregulation (CA) operates at the level of the end-organ by stabilizing CBF against dynamic changes in blood pressure through myogenic and neurogenic mechanisms (Zhang et al, 2002). From a dynamic systems perspective, the operation of the arterial baroreflex and CA in tandem provides a safeguard to ensure that the brain receives a stable blood supply. If both of these control systems fail cerebral perfusion may be compromised. As Faes et al (2013) reported, reductions in both cardiac baroreflex modulation of blood pressure and cerebral autoregulation occur prior to syncope. In individuals prone to syncope head-up tilt is associated with impaired cerebral autoregulation and an inability to activate the cardiac baroreflex compared to individuals not prone to syncope (Bari et al, 2017)

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