Changes in haemorheology in the racing greyhound as related to oxygen delivery.

Arterial blood samples were obtained from six greyhounds during rest, immediately before, and after a 704-m (7/16th mile) race. Measurements were made of various haematological (red cell count, haemoglobin, packed cell volume, white cell count, plasma proteins) and haemorheological variables. Blood and plasma viscosity were determined at high wall shear stresses (67-200 dynes.cm-2, 670-2000 microN.cm-2) in a 20-microns glass capillary device which was designed to take the diameter dependence of blood viscosity (Fahraeus-Lindqvist effect) into account. Compared to values at rest, substantial haemoconcentration occurred before the race, mainly due to splenic discharge of red cells. Additional haemoconcentration was found after the race. The increase of effective blood viscosity caused by elevation of packed cell volume was greater than the increase in O2 binding capacity resulting from the elevated haemoglobin concentration, suggesting that the haemoconcentration observed in the exercising greyhound does not enhance O2 delivery to skeletal muscle. The main physiological effect of red cell discharge from the contracting spleen appeared to be a consequence of the volume rather than the composition of the circulating blood.