Shear stress and cerebrovascular function during acute isometric exercise: the role of exercise intensity and aging

Abstract

Introduction: Exercise reduces the risk of developing vascular dysfunction, implicated in the progression of cardiovascular and cerebrovascular diseases. However, our understanding of how exercise can be optimised for improvements in brain health with increasing age, is limited. In the peripheral vasculature, episodic increases in blood flow and shear-stress promote acute and chronic improvements in vascular function. At the brain, evidence is less clear. Increases in cerebral blood flow (CBF) and shear stress are observed with low-intensity exercise, and these responses are dampened in older compared with younger adults. Whether the CBF shear stress response is intensity- and age-dependent is not known. In older adults, attenuations in CBF during exercise may be related to impaired vascular function, or an attenuated response to increases in blood pressure (hysteresis). Our study aims to examine CBF during varying increases in exercise intensity using isometric handgrip exercise. It is hypothesised that higher intensity isometric exercise will be associated with increased blood pressure and CBF, including shear-mediated internal carotid artery (ICA) dilation in young adults, but not in older adults. We also hypothesise CBF will not be associated with changes in blood pressure during exercise in older adults.