Splenic red cell sequestration and blood volume measurements in conscious pigs.

When estimated by the dilution of 51Cr-labeled red blood cells under nearly basal conditions, immature splenectomized pigs (n = 20) had a circulating red cell volume of 17.8 +/- 1.64 (SD) ml/kg. At an assumed body-to-large vessel hematocrit (BH:LH) ratio of 0.9, plasma volume was 49.6 +/- 3.12 ml/kg and blood volume 67.3 +/- 3.67 ml/kg. Sham-operated pigs (n = 20) had a circulating red cell volume of 16.2 +/- 1.39 ml/kg, a plasma volume of 51.1 +/- 3.42 ml/kg, and blood volume of 67.2 +/- 4.12 ml/kg. Kinetic analysis of early 51Cr loss from the circulating blood of the sham-operated pigs indicated a splenic red cell sequestration of 4.5 +/- 0.89 ml/kg and a t1/2 of 9.76 +/- 1.93 min for splenic red cell turnover. Epinephrine injection (n = 6) and physical restraint (n = 8) caused rapid mobilization of splenic red blood cells in sham-operated pigs. Volume estimates in splenectomized pigs (n = 7) based on simultaneous dilutions of 51Cr-labeled red blood cells and 125I-labeled bovine albumin gave circulating red cell, plasma, and blood volumes of 18.4 +/- 2.46, 60.7 +/- 4.01, and 79.0 +/- 3.51 ml/kg, respectively, and a BH:LH ratio of 0.756 +/- 0.029. The latter value may have reflected an overestimation of plasma volume by the 125I-labeled albumin procedure.