Haemorheology and exercise: intrinsic flow properties of blood in marathon running

Haemorheological and haematological parameters were studied in venous blood samples taken from 8 endurance-trained athletes before and after a marathon run. Viscometry was performed in a 20 microns glass capillary and in a Couette viscometer. Apparent blood viscosity was lower in the capillary than in the rotational viscometer, but significant differences between pre- and post-run samples were not observed in either system. This is presumably due to the absence of changes of haematocrit (pre-run [mean +/- SD]: 0.453 +/- 0.016, post-run: 0.456 +/- 0.018). Although protein concentration increased significantly from 70.8 +/- 2.1 g/l (pre-run) to 76.0 +/- 3.9 g/l (post-run), the difference of plasma viscosity was not statistically significant (pre-run: 1.26 +/- 0.03 cP, post-run: 1.30 +/- 0.07 cP). In all samples, plasma viscosity showed a significant positive correlation with total protein, globulin, albumin, but not with fibrinogen concentration. Cone-plate aggregometry and a filtration technique were used to evaluate red cell aggregation and deformability, two determinants of blood rheology which also were not different between pre- and post-run samples. The absence of viscosity changes in relation to the marathon run may be due to the relative stability of blood and plasma volume, which can be deduced from haematological parameters. Alterations of plasma composition (e.g. acidosis or hyperosmolality) seem to cause only minor, if any, changes of microrheological cell properties.