Could exercise-induced increase in blood viscosity at high shear rate be entirely explained by hematocrit and plasma viscosity changes?

Abstract

Exercise-induced increase in blood viscosity is supposed to result from modifications in plasma viscosity and hematocrit, while erythrocyte rigidity remains constant. If this assumption is valid, the equations of Quemada and Dintenfass can be used to predict postexercise blood viscosity (μb) at high shear rate from h (hematocrit) and μpl (plasma viscosity), assuming that erythrocyte rigidity (k or Tk) remains constant. We first investigated this hypothesis in 21 children (5 girls, 16 boys, age: 9–15 yr) during a 15 min submaximal exercise (final step: 90% of maximal power output). Values calculated with both equations were highly correlated with measured postexercise μb: (respectively r=0.932 and r=0.936; p<0.001 for both) i.e. increases in h and μpl statistically “explain” 87% of the variance of μb increase. In a second study the same procedure was applied to 8 highly trained professional football players during a longer exercise-test (ten minutes of increasing workload followed by a 15 min plateau at 85% of the maximal power output). In this case prediction of μb from h and μpl alone gave very poor results, due to an increase in ‘Tk’ and ‘k’ which was observed (p<0.01) when lactatemia exceeded 4 mmol/l. This increase (deltaTk) is correlated with the increase in blood lactate (r=0.562 p<0.01). Thus, our data suggest that (a) as previously described, μpl and h appear to be the main predictors of postexercise μb in most exercise protocols; (b) however, in some cases, e.g. when blood lactate increases above 4 mmol/l, RBC rigidity can be also increased, and changes in μpl and h are no longer the only determinants of postexercise μb.