Cardiovascular dynamics during exercise are related to blood rheology

Abstract

Background: The principal determinants of oxygen uptake ($\Vdot$O₂) kinetics are controversial, with dynamic changes in central and peripheral factors mediating oxygen supply and utilisation suggested to be limiting. The aim of this study was to determine whether important parameters of blood rheology were related to the exercise-induced time-course changes in $\Vdot$O₂ and cardiac output ($\Qdot$c), or steady-state arteriovenous oxygen difference (a-vO₂D) during submaximal cycling. Methods and Results: Blood was collected from ten healthy, recreationally active males and females (age: 21.7 ± 1.3 yr; body mass index: 22.7 ± 2.0 kg·m⁻²), before each subject cycled at 105% of the first ventilatory threshold. Red blood cell aggregation was negatively correlated with steady-state $\Vdot$O₂ during exercise and the a-vO₂D at rest (r = −0.73, p < 0.05), and positively correlated to $\Qdot$c at rest (r = 0.71, p < 0.05). Blood viscosity at various shear rates was negatively correlated with the time constant of $\Vdot$O₂ (all p < 0.01) on-transient kinetics. Red blood cell deformability at various shear stress was positively correlated to the time constant of $\Vdot$O₂ (all p < 0.05) on-transient kinetics. Conclusions: The findings of the present study suggest that the rheological properties of blood may modulate, at least in part, the rate of change in the uptake and/or utilisation of oxygen at the onset of exercise.