Abstract
PurposeWe investigated the effect of handgrip (HG) maneuver on time-varying estimates of dynamic cerebral autoregulation (CA) using the autoregressive moving average technique.MethodsTwelve healthy subjects were recruited to perform HG maneuver during 3 minutes with 30% of maximum contraction force. Cerebral blood flow velocity, end-tidal CO2 pressure (PETCO2), and noninvasive arterial blood pressure (ABP) were continuously recorded during baseline, HG and recovery. Critical closing pressure (CrCP), resistance area-product (RAP), and time-varying autoregulation index (ARI) were obtained.ResultsPETCO2 did not show significant changes during HG maneuver. Whilst ABP increased continuously during the maneuver, to 27% above its baseline value, CBFV raised to a plateau approximately 15% above baseline. This was sustained by a parallel increase in RAP, suggestive of myogenic vasoconstriction, and a reduction in CrCP that could be associated with metabolic vasodilation. The time-varying ARI index dropped at the beginning and end of the maneuver (p<0.005), which could be related to corresponding alert reactions or to different time constants of the myogenic, metabolic and/or neurogenic mechanisms.ConclusionChanges in dynamic CA during HG suggest a complex interplay of regulatory mechanisms during static exercise that should be considered when assessing the determinants of cerebral blood flow and metabolism.
Highlights
The neurovascular response to exercise and augmented cerebral metabolic demand relies on dynamic adjustments of multivariate systems, involving myogenic, metabolic and neurogenic mechanisms that lead to constriction or dilation of cerebral arteriolar smooth muscles in order to control cerebral blood flow [1,2]
It has been demonstrated that handgrip maneuver (HG) exercise induces changes in cerebral blood flow (CBF), possibly due to bilateral activation of cortical brain areas implicated in muscle contraction and autonomic regulation [7,10]
PETCO2 showed a trend to increase from baseline to the 2nd min of the maneuver, these changes were not significant (Fig. 2)
Summary
The neurovascular response to exercise and augmented cerebral metabolic demand (neurovascular coupling) relies on dynamic adjustments of multivariate systems, involving myogenic, metabolic and neurogenic mechanisms that lead to constriction or dilation of cerebral arteriolar smooth muscles in order to control cerebral blood flow [1,2] This response is mediated by the neurovascular unit through activation of neuronal cells such as astrocytes and release of neurotransmitters [3]. It has been demonstrated that HG exercise induces changes in cerebral blood flow (CBF), possibly due to bilateral activation of cortical brain areas implicated in muscle contraction and autonomic regulation [7,10] These effects, and concomitant changes in ABP, have allowed the HG maneuver to be used for assessment of dynamic cerebral autoregulation (CA) [10,11,12,13,14,15]. This limitation resulted from techniques adopted to assess dynamic CA, such as transfer function analysis [10] or sudden release of compressed thigh cuffs [14]
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