Relationships between hemodynamic, hemorheological and metabolic responses during exercise

摘要

Aerobic performance is dependent on both cardio-respiratory and peripheral factors with hemodynamic parameters playing a major role. However, whether blood rheology might affect aerobic performance through an effect on hemodynamic factors is not known. The aim of the present study was to assess the relationships between hemodynamic, hemorheological and metabolic parameters in response to a sub-maximal cycling exercise protocol consisting of three successive levels of nine min duration (50, 100 and 150 W). Ten young sportsmen participated in the present study. Mean arterial pressure (MAP) was measured manually, with thoracic impedance used to monitor cardiac output (Q_c): systemic vascular resistance (SVR) was then calculated. Whole blood viscosity (η_b) was measured and used to calculate systemic vascular hindrance. Hematocrit (Hct) was determined by micro-centrifugation and red blood cell (RBC) deformability (EI) was determined by ecktacytometry. A breath-by-breath gas analyzer was used to measure oxygen uptake (V_(O_2)); the Fick equation was used to calculate arterio-venous oxygen difference [(a-v)O_2] from V_(O_2) and Q_c. All measurements were performed at rest, during exercise and during recovery. Compared to baseline, Q_c, MAP, Hct, EI, V_(O_2), and (a-v)O_2 increased during exercise. η_b increased above baseline only at 150 W and remained elevated during recovery; the increase in η_b during the last level of exercise was associated with a decrease of SVR and systemic vascular hindrance. There was a significant negative correlation between EI and SVR (r = -0.35, p < 0.01) and a significant positive relationship between EI and (a-v)O_2 (r = 0.35, p < 0.01) and between EI and V_(O_2) (r = 0.37, p < 0.01) across all exercise workloads, thus suggesting a potential role for RBC deformability as a factor affecting aerobic performance via oxygen delivery to tissues. These data lend support to the concept that hemorheological parameters may contribute to hemodynamic and cardio-respiratory adaptations in response to exercise in moderately trained sportsmen.