Influence Of Cardiac Output Response To The Onset Of Exercise On Cerebral Blood Flow

Abstract

It is reported that the changes in cardiac output (Q) contribute to cerebral blood flow (CBF) regulation at rest and even during steady-state exercise. At the onset of cycling exercise, cardiac output (Q) increases acutely and largely via muscle pump, which may cause a larger elevation in CBF than an adequate value. However, the relationship between Q and CBF at the onset of exercise remains unknown. PURPOSE: The purpose of the present study was to examine whether onset exercise-induced large increase in Q contributes to CBF regulation at the onset of exercise. METHODS: In 11 young healthy participants, Q, mean arterial pressure (MAP), and mean blood velocities of middle and posterior cerebral arteries (MCA Vm and PCA Vm, respectively) were continuously measured during a 3-min light cycling exercise at 20 W on the ergometer. RESULTS: At the onset of exercise, Q increased acutely to the peak (P < 0.001), while MCA Vm and PCA Vm had two nadir and peak responses, but these CBF changes were not significant (MCA Vm and PCA Vm; P = 0.461 and P = 0.125, respectively). The change in Q was correlated with that of MCA Vm or PCA Vm from resting baseline to the steady-state exercise (r = 0.371, P = 0.008 and r = 0.418, P = 0.003, respectively). However, interestingly, the change in Q was not correlated with that of MCA Vm or PCA Vm at the onset of exercise (P = 0.223 and P = 0.151, respectively). CONCLUSION: These findings indicate that the change in Q does not contribute to CBF regulation at the onset of exercise for protecting cerebral vasculature against a large and acute elevation in Q at the onset of exercise.