Plasma volume shifts during moderate exercise in splenectomized greyhounds

1. Plasma volume was measured in splenectomized greyhounds, using T-1824, and sequential changes in plasma volume were measured using two independent methods, based on T-1824 plasma decay characteristics and on changes in haematocrit. 2. There were no significant differences between estimates of plasma volume made by the two methods in resting or exercising dogs. Therefore it was concluded that the characteristics of the decay of dye concentration in plasma were not affected by exercise and that sequential determinations of plasma volume from a single dye injection provide a valid determination of plasma volume during exercise in dogs. 3. During submaximal exercise, the plasma volume increased by 0-11.8% of its initial value. In no case did plasma volume decrease significantly. 4. An increase in plasma volume during excercise was also seen in animals previously made acutely hypervolemic or hypovolemic. 5. It is suggested that the increase in plasma volume constitutes part of a mechanism maintaining oxygen delivery to tissues during exercise.