ESTIMATION OF SPLENIC VOLUME AND ITS RELATIONSHIP TO LONG-DURATION APNEA IN SEALS

Splenic volume was estimated in northern elephant seal pups (Mirounga angustirostris) by calculating the reservoir volume required to accommodate measured shifts in hematocrit that occur during periods of sleep-associated apnea. In vivo total estimated splenic mass for 15 pups represented 2.8% of body mass, while adult female seal splenic mass was estimated to be between 7.3% and 10.5% of body mass, considerably higher than that of terrestrial mammals. The model was applied to several other species of pinnipeds. Splenic mass estimates by this method were in agreement with previously reported values obtained for some pinniped species by computerized axial tomography (CT) scan. The data suggest that splenic mass in seals is correlated to the blood volume to body mass ratio and that the large spleen of seals is an anatomical consequence of the increased phocid blood volume.