Effect Of Gravity-induced Intracranial Pressure Changes On Cerebral Blood Flow Regulation During Resistance Exercise

The common carotid artery (CCA) bifurcates at the carotid sinus into the internal carotid artery (ICA), responsible for supplying blood to the brain, and the external carotid artery (ECA), which supplies blood to the face and the neck. During resistance exercise, there is heterogeneous regulation of cerebral blood flow, marked by vasoconstriction in the ICA and vasodilation in the ECA. Interestingly, at rest, changes in posture do not affect ICA blood flow (BF), whereas ECA blood flow increases with the increasing intracranial pressure (ICP) associated with postural changes. PURPOSE: This study aimed to verify the hypothesis that gravity-induced increases in ICP would further reduce ICA blood flow and elevate ECA blood flow during resistance exercise as exercise intensity increases. METHODS: Sixteen healthy adults (8 M/8F, 22 ± 2 yrs, mean ± SD) performed two different intensities of isometric knee extension exercises for 5 min each in the supine and sitting positions. Exercise intensity was set at 5% and 20% of maximum voluntary contraction. After completing two exercises in one posture, the next two exercises were performed after 20 min of rest in the second posture. The diameter and velocity of the ICA and ECA were simultaneously measured during the last 30 s of rest and exercise using Doppler ultrasound. Intraocular pressure (IOP) was measured as an index of hydrostatic changes in ICP. RESULTS: IOP was higher in the supine position than in the sitting position (P < 0.01). Increased exercise intensity in both positions caused a decrease in regional distribution from CCA to ICA, and an increase in regional distribution from CCA to ECA from their respective resting values (interaction P = 0.50, main effect of trial P < 0.01). However, the contribution from CCA to ECA was greater in the supine position compared with that in the sitting position (main effect of posture P < 0.01). CONCLUSIONS: The present results suggest that during resistance exercise, the postural change-associated increase in ICP promotes vasodilation in the peripheral vascular bed of ECA and decreases blood flow distribution to the ICA with increasing exercise intensity. This heterogeneous nature of intra- and extracranial blood flow may serve to prevent excessive cerebral perfusion during resistance exercise, particularly in the supine position. JSPS KAKENHI Grant Number 20 K11186