Interindividual relationships between baroreflex sensitivity and cerebral autoregulation in healthy humans

Maintenance of adequate cerebral perfusion during normal physiological challenges requires integration between cerebral blood flow (CBF) and systemic blood pressure (BP) control mechanisms. Previous studies have shown that cardiac baroreflex sensitivity (BRS) is inversely related to some measures of cerebral autoregulation (CA). 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, cerebral blood flow velocity (CBFv) 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 CBF control was quantified using transfer function analysis (TFA) metrics derived during rest and Tieck’s autoregulatory index (ARI) following bilateral thigh cuff deflation. Sympathetic BRS during modified Oxford trials was inversely related to ARI (R = 0.64, P = 0.03). Sympathetic BRS during spontaneous baseline was positively related to TFA gain (R = -0.74, P = 0.01). Resting integrated MSNA per 100 heartbeats was also inversely related to TFA Gain (R = 0.57, P = 0.06). 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. Such interactions may explain the physiological diversity inherent in functionally redundant systems engaged in the regulation of end organ blood flow