Regulation of cerebral blood flow and metabolism during exercise

Abstract

Cerebral function in humans is critically dependent upon continuous oxygen delivery, metabolic nutrients and active regulation of cerebral blood flow (CBF). As a consequence, cerebrovascular function is precisely titrated by multiple physiological mechanisms, characterised by complex integration, synergism and protective redundancy. At rest, adequate CBF is regulated through reflexive responses in the following order of regulatory importance: fluctuating arterial blood gases (in particularly partial pressure of carbon dioxide [PaCO₂]), cerebral metabolism, arterial blood pressure, neurogenic activity and cardiac output. Unfortunately, the magnitude that these integrative and synergistic relationships contribute to governing the CBF during exercise remains unclear. Despite some evidence indicating that CBF regulation during exercise is dependent on the changes of blood pressure, neurogenic activity and cardiac output, their role as a primary governor of the CBF response to exercise remains controversial. In contrast, the balance between PaCO₂ and cerebral metabolism continues to gain empirical support as the primary contributors to the intensity dependent changes in CBF observed during submaximal, moderate and maximal exercise. The goal of this review is to summarize the fundamental physiology and mechanisms involved in regulation of CBF and metabolism during exercise. The clinical implications of a better understanding of CBF during exercise and new research directions are also outlined.

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