Effects of increased splenic arterial flow and venous pressure on splenic red cell accumulation.

The importance of increments in splenic venous pressure (SVP) and splenic arterial flow (SAF) for splenic red cell accumulation was estimated in 14 anesthetized dogs with the spleen in situ by arterial and splenic venous hematocrit measurements and continuous ultrasonic recording of splenic diameter (SD). A 10-mmHg increase in SVP by 4 min of splenic venous constriction reduced SAF by 32 +/- 5%, increased SD by 5.1 +/- 0.8%, and transiently reduced splenic venous hematocrit, measured every 10 s, from 35.4 +/- 1.4 to a minimum of 29.2 +/- 1.8%. A 10-mmHg rise in SVP by 4 min of saline infusion increased SAF by 178 +/- 25% and SD by 16.1 +/- 3.0%, and splenic venous hematocrit declined more rapidly and to a lower value than arterial hematocrit. Blood volume expansion with saline or blood at constant, 10-mmHg elevated SVP confirmed that splenic red cell accumulation was greater during blood volume expansion than during splenic venous constriction. We conclude that the spleen accumulates red cells when SVP is raised. At constant, elevated SVP splenic red cell accumulation is flow dependent.