Cardiovascular dynamics during exercise are related to blood rheology

Background: The principal determinants of oxygen uptake ( /VdotO2) 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 /VdotO2 and cardiac output ( /Qdotc), 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 ᠱ.3 yr; body mass index: 22.7 ᠲ.0 kg筭2), before each subject cycled at 105% of the first ventilatory threshold. Red blood cell aggregation was negatively correlated with steady-state /VdotO2 during exercise and the a-vO2D at rest (r = -0.73, p < 0.05), and positively correlated to /Qdotc at rest (r = 0.71, p < 0.05). Blood viscosity at various shear rates was negatively correlated with the time constant of /VdotO2 (all p < 0.01) on-transient kinetics. Red blood cell deformability at various shear stress was positively correlated to the time constant of /VdotO2 (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.No Full Tex

Blood viscosity and hemodynamics during exercise

We tested the effects of submaximal exercise on blood viscosity (?(b)), nitric oxide production (NO) and hemodynamics. Relationships between the exercise-induced changes that occurred in these parameters were investigated. Nine subjects performed exercise for 15 min at 105% of the first ventilatory threshold. Mean arterial pressure (MAP) and cardiac output (Qc) were measured, allowing the determination of systemic vascular resistance (SVR). Blood was sampled at rest and at the end of exercise. The ?(b) was determined at high shear rate and was used to calculate systemic vascular hindrance (VH). NO production was estimated by measuring plasma concentrations of NO stable end products (NOx). Qc, MAP, ?(b) and NOx, increased with exercise, whereas SVR and VH decreased. The changes between rest and exercise were calculated and tested for correlations. We observed: 1) a positive correlation between the increase in ?(b) and the increase in NOx; 2) a negative correlation between the increase in NOx and the decrease in VH; 3) a negative correlation between the increase in ?(b) and the decrease in SVR. Although the increase in Qc and blood flow during exercise probably promoted NO production due to shear dependent stimulation of the endothelium, the present results also support that the rise in ?(b) during exercise may be necessary for NO production and adequate vasodilation.No Full Tex