Ursula B Windberger, Roland Auer and Malcolm J Smale
Blood O2-store in diving animals is increased by great numbers of large erythrocytes which carry enhanced hemoglobin contents. In seal and dolphin, resting hemato (HCT) and/or Red Blood Cell (RBC) indices were elevated (HCT: seal: 50 (47/51); dolphin: 45/50); MCH: seal: 35.8 (34.4/37.3); dolphin: 41/40); MCHC: seal: 33.9 (33.4/36.0); dolphin: 35.6/36.6), and RBC volume was increased (seal: 101 (99/110); dolphin: 115/110 fL) compared to terrestrial animals and man. However, WBV increases in parallel with the HCT. In seal, we therefore calculated the range in which the desired HCT effect is not weakened by an increase of WBV; we plotted the theoretical oxygen transport capacity (WBV*HCT-1) against the HCT. A quadratic regression showed that the resting HCT was higher than the optimal HCT value (at 11.6 s-1: 31%; 40.5 s-1: 37%; 267 s-1: 45%; all: p<0.05). This may facilitate blood stasis during a dive, when HCT is further increased through splenic release of RBC. Flow curves of seals showed shear thinning (11.6/500: seal: 1.98 (1.87/2.11), indicating that the blood texture changes with shear rates. RBC deformability in seals was pronounced (elongation index (ectacytometry) at 60Pa: females: 32, 29; males: 24, 24), but aggregability was low (aggregation indices M0: 3.15 (1.6/4.8); M1: 13.3 (8.7/18.8)), and therefore intermediate regarding Weddell seal (high aggregability) and ringed seal (nil). Considering the importance of aggregability on the cell free layer width in arterioles, feeding of RBC into subsequent vessels at bifurcations may be enhanced.
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