35 CONTRIBUTIONS OF PLASMA, SERUM AND RED BLOOD CELLS (RBC) TO VICOSITY REDUCTION OF BLOOD FROM TERM AND PRETERM INFANTS STUDIED IN NARROW TUBES:

In blood vessels and in artificial tubes with diameters of less than 500 μm blood viscosity decreases with decreasing tube diameter (Fahraeus - Lindqvist effect). For RBC-buffer suspensions this effect is stronger for neonatal than for adult RBC.(Pediatr.Res.25:595, 1989) In the present investigation we studied the effect of autologous plasma, adult plasma and serum on the viscosity of RBC from 10 adults, 10 term and 10 preterm inlanls. The hematocrits of the samples were adjusted at 20, 40 and 60 %. Glass tubes with diameters of 270, 100 and 55 μm were perfused with these suspensions. The table shows the viscosity reductions for RBC suspensions with a hematocrit of 60 % when going from 270 to 55 μm tubes. At a given feed hematocrit there was no difference in viscosity reduction among the suspension media in the three age groups. We conclude that differences in Fahraeus-Linqvist effect among adults, term and preterm neonates are due to specific properties of RBC and independent of plasma properties.