26 FLOW BEHAVIOR OF NEONATAL AND ADULT ERYTHROCYTES IN VESSELS WITH DIAMETERS OF 3 TO 6 μm

This study was designed to analyse the flow behavior of red blood cells (RBC) by means of a mathematical model. According to this model, the flow resistance depends on the gap between RBC and vessel wall and on the plasma viscosity. Surface area (SA) and volume (V) of RBC from ten term neonates (N) and ten adults (A) were measured by means of a micropipette system and plasma viscosity (PV) was determined using a capillary viscometer. Neonatal RBC had larger V and SA than adult RBC (107 ± 6 vs 90±4 fl, and 154±7 vs 137±7 μm3). PV was lower in neonates (1.04±0.10 cP) than in adults (1.26±0.13 cP). The critical vessel diameter below that the gap becomes too small to allow sufficient lubrication is higher for neonatal RBC (3.3μm) than that for adult RBC (2.9μm). The driving pressure, hematocrit and viscosity of neonatal RBC is higher than that of adult RBC if both cell types have been suspended in the same medium. However, the driving pressure and viscosity of neonatal and adult RBC is similar for neonatal and adult RBC if the cells have been suspended in the corresponding neonatal and adult plasma. We conclude that the flow properties of neonatal and adult RBC in vessels with diameters of 3.5 to 6 μm are not different since the larger size of neonatal RBC is compensated by a lower PV.