title: Exercise intensity modulates brachial artery retrograde blood flow and shear rate during leg cycling in hypoxia.
abstract: The purpose of this study was to elucidate the effect of exercise intensity on retrograde blood flow and shear rate (SR) in an inactive limb during exercise under normoxic and hypoxic conditions. The subjects performed two maximal exercise tests on a semi-recumbent cycle ergometer to estimate peak oxygen uptake (V˙O2peak) while breathing normoxic (inspired oxygen fraction [FIO2 = 0.21]) and hypoxic (FIO2 = 0.12 or 0.13) gas mixtures. Subjects then performed four exercise bouts at the same relative intensities (30 and 60% V˙O2peak) for 30 min under normoxic or hypoxic conditions. Brachial artery diameter and blood velocity were simultaneously recorded, using Doppler ultrasonography. Retrograde SR was enhanced with increasing exercise intensity under both conditions at 10 min of exercise. Thereafter, retrograde blood flow and SR in normoxia returned to pre-exercise levels, with no significant differences between the two exercise intensities. In contrast, retrograde blood flow and SR in hypoxia remained significantly elevated above baseline and was significantly greater at 60% than at 30% V˙O2peak. We conclude that differences in exercise intensity affect brachial artery retrograde blood flow and SR during prolonged exercise under hypoxic conditions.
authors.affiliation: School of Health Sciences, Sapporo Medical University, Sapporo, Japan e.iwamoto@sapmed.ac.jp.
authors.forename: Erika
authors.initials: E
authors.lastname: Iwamoto
authors.affiliation: Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan Graduate School of Medicine, Nagoya University, Nagoya, Japan.
authors.forename: Keisho
authors.initials: K
authors.lastname: Katayama
authors.affiliation: Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, Japan Graduate School of Medicine, Nagoya University, Nagoya, Japan.
authors.forename: Koji
authors.initials: K
authors.lastname: Ishida
keywords: Aerobic exercise; exercise intensity; hypoxia; retrograde shear rate