Acute aerobic exercise enhances cerebrovascular shear-mediated dilation in young adults: The role of cerebral shear

Exercise-induced increases in shear rate (SR) acutely improve peripheral endothelial function, but the presence of this mechanism in cerebral arteries remains unclear. Thus, we evaluated shear-mediated dilation of the internal carotid artery (ICA), which is an index of cerebrovascular endothelial function, before and after exercise. Shear-mediated dilation was measured using 30 s of hypercapnia in 16 young adults before and 10 min after 30 min of sitting rest (CON) or three cycling exercises on four separate days. The target exercise intensity was 80% of oxygen uptake at the ventilatory threshold. To manipulate the ICA SR during exercise, participants breathed spontaneously (Ex_SB, SR increase) or hyperventilated without (Ex_HV, no increase in SR) and with adding CO₂ to inspiratory air (Ex_HV+CO2, restoration of SR increase). Shear-mediated dilation was calculated as a percent increase in diameter from baseline. Doppler ultrasound measures ICA velocity and diameter. The CON trial revealed that 30 min of sitting unaltered shear-mediated dilation (4.34 ± 1.37% to 3.44 ± 1.23%, P = 0.052). ICA dilation after exercise compared with pre-exercise levels increased in the Ex_SB trial (3.32 ± 1.37% to 4.74 ± 1.84%, P < 0.01), remained unchanged in the Ex_HV trial (4.07 ± 1.55% to 3.21 ± 1.48%, P = 0.07), but elevated in the Ex_HV+CO2 trial (3.35 ± 1.15% to 4.33 ± 2.12%, P = 0.04). Our results indicate that exercise-induced increases in cerebral shear may play a crucial role in improving cerebrovascular endothelial function following acute exercise in young adults.