Cardiac output and leg and arm blood flow during incremental exercise to exhaustion on the cycle ergometer

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Abstract
To determine central and peripheral hemodynamic responses to upright leg cycling exercise, nine physically active men underwent measurements of arterial blood pressure and gases, as well as femoral and subclavian vein blood flows and gases during incremental exercise to exhaustion (Wmax). Cardiac output (CO) and leg blood flow (BF) increased in parallel with exercise intensity. In contrast, arm BF remained at 0.8 l/min during submaximal exercise, increasing to 1.2 ± 0.2 l/min at maximal exercise ( P < 0.05) when arm O2 extraction reached 73 ± 3%. The leg received a greater percentage of the CO with exercise intensity, reaching a value close to 70% at 64% of Wmax, which was maintained until exhaustion. The percentage of CO perfusing the trunk decreased with exercise intensity to 21% at Wmax, i.e., to ∼5.5 l/min. For a given local V̇o2, leg vascular conductance (VC) was five- to sixfold higher than arm VC, despite marked hemoglobin deoxygenation in the subclavian vein. At peak exercise, arm VC was not significantly different than at rest. Leg V̇o2 represented ∼84% of the whole body V̇o2 at intensities ranging from 38 to 100% of Wmax. Arm V̇o2 contributed between 7 and 10% to the whole body V̇o2. From 20 to 100% of Wmax, the trunk V̇o2 (including the gluteus muscles) represented between 14 and 15% of the whole body V̇o2. In summary, vasoconstrictor signals efficiently oppose the vasodilatory metabolites in the arms, suggesting that during whole body exercise in the upright position blood flow is differentially regulated in the upper and lower extremities.