| Summary: | 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 VO₂, ten minutes at a PO requiring 50% of
maximal VO₂ and 10 minutes at a PO requiring 75% of maximal VO₂.
Red cell volume (RCV), plasma volume (PV) were directly measured
pre- and post-exercise using radioisotope labeling (⁵¹Cr, ¹²⁵| -
RHISA, ¹³¹I-RHISA). Hematocrit (Hct) was measured and the spleen
was imaged, using ⁹⁹[sup 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 pre- to 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%.
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