Regulation of Cerebral Blood Flow During Exercise

Abstract

Constant cerebral blood flow (CBF) is vital to human survival. Originally thought to receive steady blood flow, the brain has shown to experience increases in blood flow during exercise. Although increases have not consistently been documented, the overwhelming evidence supporting an increase may be a result of an increase in brain metabolism. While an increase in metabolism may be the underlying causative factor for the increase in CBF during exercise, there are many modulating variables. Arterial blood gas tensions, most specifically the partial pressure of carbon dioxide, strongly regulate CBF by affecting cerebral vessel diameter through changes in pH, while carbon dioxide reactivity increases from rest to exercise. Muscle mechanoreceptors may contribute to the initial increase in CBF at the onset of exercise, after which exercise-induced hyperventilation tends to decrease flow by pial vessel vasoconstriction. Although elite athletes may benefit from hyperoxia during intense exercise, cerebral tissue is well protected during exercise, and cerebral oxygenation does not appear to pose a limiting factor to exercise performance. The role of arterial blood pressure is important to the increase in CBF during exercise; however, during times of acute hypotension such as during diastole at high-intensity exercise or post-exercise hypotension, cerebral autoregulation may be impaired. The impairment of an increase in cardiac output during exercise with a large muscle mass similarly impairs the increase in CBF velocity, suggesting that cardiac output may play a key role in the CBF response to exercise. Glucose uptake and CBF do not appear to be related; however, there is growing evidence to suggest that lactate is used as a substrate when glucose levels are low. Traditionally thought to have no influence, neural innervation appears to be a protective mechanism to large increases in cardiac output. Changes in middle cerebral arterial velocity are independent of changes in muscle sympathetic nerve activity, suggesting that sympathetic activity does not alter medium-sized arteries (middle cerebral artery).CBF does not remain steady, as seen by apparent increases during exercise, which is accomplished by a multi-factorial system, operating in a way that does not pose any clear danger to cerebral tissue during exercise under normal circumstances.

A Physiological Approach to Prolonged Recovery From Sport-Related Concussion

“…29 Elevated CBF was associated with the development of headache and dizziness, which significantly limited exercise tolerance in the PCS patients. 55 We hypothesize that cerebral autoregulation, which allows the brain to maintain an almost constant perfusion pressure in the face of varying systemic BPs, 56,57 is abnormal after concussion. 58 If so, then changes in systemic BP will induce excessive changes in cerebral perfusion pressure in concussed patients and produce symptoms such as headache.…”

The influence of anesthesia and fluid–structure interaction on simulated shear stress patterns in the carotid bifurcation of mice

“…At high locomotor activity, the cardiac output increases because of an increase in blood flow towards the skeletal muscles, while the main perfusion area of the carotid arteries is the brain (Marieb and Hoehn, 2008). In humans, the cerebral blood flow only peaks at the onset of physical activity and decreases again during constant physical activity, while the cardiac output is still at an elevated level (Querido and Sheel, 2012). The initial increase due to physical exercise (steady-state cycling) has been quantified for healthy humans as 27.9 ± 28.6% and the increase during prolonged exercise has been reported 2.6 ± 13.5% (Hiura et al, 2014).…”

Cerebral blood flow and cerebrovascular reactivity at rest and during sub-maximal exercise: Effect of age and 12-week exercise training

“…In addition to the CBF response, cerebrovascular CO 2 reactivity is also increased during exercise (Ogoh et al 2008;Rasmussen et al 2006). Although the effects of exercise on CBF Querido and Sheel 2007) and cerebrovascular reactivity (Ogoh et al 2008;Rasmussen et al 2006) have been relatively well documented in young individuals, any influencing effect of older age on these parameters has not been established. Due to the conflicting evidence on the effect of age on cerebrovascular reactivity at rest, it is unclear what effect (if any) age has on cerebrovascular reactivity during exercise.…”