The impact of splenic release of red cells on hematocrit changes during exercise

The purpose of this study was to determine the volume of red cells released by the spleen during exercise and to establish the impact of splenic emptying on peripheral hematocrit during exercise. The influences of training status and hypoxic exposure on splenic emptying and exercise hemodynamics were also examined. 6 trained (T) and 6 untrained (N) and 4 splenectomized (S) subjects completed a set of two tests: a maximal aerobic power test and a 30 minute exercise test (ES). The T and N groups also completed the two tests i n hypoxic conditions (FI02 = 0.16). The results of the maximal test determined the power outputs (PO) at which the subjects exercised during the exercise session. The ES consisted of 10 minutes at a FO requiring 25% of maximal V O 2 , ten minutes at a PO requiring 50% of maximal V O 2 and 10 minutes at a PO requiring 75% of maximal VO2. Red cell volume (RCV), plasma volume (PV) were directly measured preand post-exercise using radioisotope labeling ( 5 1Cr, 1 2 5 | RHISA, 1 3 1I-RHISA). Hematocrit (Hct) was measured and the spleen was imaged, using 9 9 m Tc, pre-exercise and after each 10 minute workload. Spleen volume (SV) was calculated using the average count of the anterior and posterior scan and the count of a known volume of blood. There was no difference in pre-exercise RCV between the S group (2033 mL) and the N group (2058 mL). The N group showed a significant increase in RCV in both normoxic and hypoxic conditions post-exercise (p<0.05). The S group PV of 4255 mL was significantly higher than the N group PV of 3518 mL (p<0.01). Post-exercise PV in S was significantly lower than pre-exercise PV and difference between N and S pre-exercise PV disappeared. The N and T groups also showed a significant (p<0.05) decrease in PV pre-to post-exercise, in both the normoxic and hypoxic conditions, however there was no difference in that decrease between the two test conditions or between the groups. SV also decreased preto postexercise for N and T in both conditions (p<0.01). The pre-exercise SV of the N group (360 mL) was higher than that of the T group (279 mL), but when the change in SV was shown as a percentage of original SV, the decrease in SV after each exercise load was identical for both groups in both normoxic and hypoxic conditions. The volume of red cells released by the spleen ranged from 142-187 mL, representing 7-9% of total red cell volume. Both N and T showed significant increases in Hct in both exercise conditions but there was no difference between the groups or between conditions. The S group Hct readings at all test times were significantly lower than the corresponding N group Hct and did not significantly increase during exercise: Reductions in PV in the N and T groups were calculated to only cause 68-78% of the change in Hct during both normoxic-and hypoxic exercise with the increase in circulating RCV causing the remainder of the change. The results of this study demonstrate that splenic release of red cells has a significant impact on peripheral hematocrit. Aerobic fitness and hypoxic exposure does not influence the reduction in spleen volume with exercise or it's impact on hematocrit changes. The results of this study also provide evidence that indirect calculations of plasma volume changes could result in prediction errors of 22 to 33%.