Hypoxia augments oscillatory blood flow in brachial artery during leg cycling

The purpose of the present study was to elucidate changes in mean blood flow and oscillatory blood flow patterns to the inactive limb during leg cycle exercise in hypoxia. We hypothesized that oscillatory antegrade and retrograde blood flows to the nonworking limb would increase during incremental cycle exercise under hypoxic condition.

Eight males participated in this study. Two maximal exercise tests were conducted on a semirecumbent cycle ergometer while subjects inhaled a normoxic (inspired oxygen fraction [FIO2] = 0.21) or hypoxic gas mixture (FIO2 = 0.12). The exercise began at an initial power output of 30 W, and workload was increased by 30 W every 2 min until exhaustion. Brachial artery blood velocity and diameter were simultaneously recorded during exercise using Doppler ultrasonography. Blood flow was calculated using the cross-sectional area of the brachial artery and time-averaged mean blood velocity.

Mean blood flow decreased until 120 W in both trials (P < 0.05), and the magnitude of the reduction in mean blood flow was not different between two trials. However, the extent of changes in antegrade and retrograde blood flows during submaximal exercise in hypoxia was greater than that in normoxia (normoxia vs hypoxia: antegrade blood flow at 120 W = 145.4 ± 10.3 vs 172.4 ± 9.0 mL·min and retrograde blood flow at 120 W = -89.1 ± 4.9 vs -118.1 ± 6.2 mL·min, P < 0.05).

These results indicate that hypoxia has a significant effect on oscillatory antegrade/retrograde blood flow patterns in nonworking limb during cycling exercise.