Fahraeus and fahraeus-lindqvist effects for neonatal and adult red blood cell suspensions

Abstract

In blood vessels with diameters less than 500 μm, both the hematocrit and viscosity decrease with decreasing tube diameter [Fahraeus effect (FE) and Fahraeus-Lindqvist effect (FLE)]. Because both effects may be influenced by red blood cell (RBC) volume and osmolality, the effects of RBC type and suspending medium osmolality (216, 294, and 473 mosmol/kg) on tube hematocrit (Hi) and relative viscosity (nr) in narrow tubes (32 to 145 Mm diameter) were studied for 0.40 L/L (40%) hematocrit suspensions of human neonatal and adult RBC in buffer. Osmolality of 473 mosmol/kg caused shrinkage of RBC by 20% so that neonatal RBC assume the volume of adult RBC in isotonic buffer. The FLE and FE were present for both neonatal and adult RBC suspensions regardless of osmolality. The viscosity reduction when going from a 145- to a 32-fim tube was greatest for the hypertonic neonatal and adult RBC: changes were —44% (473 mosmol/kg) and —31% (294 mosmol/kg) for neonatal RBC, and -39% (473 mosmol/kg), -34% (294 mosmol/kg), and —21% (216 mosmol/kg) for adult RBC. The ηr were significantly lower (7% on average) for isotonic neonatal RBC compared with adult cells in 32-μm (p < 0.025), 46-μm, and 146-μm tubes (p < 0.001). In contrast, HT and thus the FE were less affected by RBC type or osmolality (only 13% change over entire range of osmolality and diameter): relative HT values were systematically lower (p < 0.02), and the FE greater, for isotonic neonatal versus adult RBC. At each osmolality, ηr increased linearly with increasing HT. However, the viscosity-HT relations differed at various osmolalities. A semiempirical model indicated that 1) HT, relative cell volume and thus mean cellular Hb concentration, and tube diameter are primary determinants of ηr, and 2) ηr can be predicted for neonatal and adult RBC in hypertonic and isotonic media over a wide range of tube diameters. We conclude that the FLE and FE are more pronounced for neonatal RBC than for adult RBC. This cannot be explained by the increased volume of neonatal RBC, because shrunk RBC showed higher FLE than RBC in isotonic solution. Increased FLE and FE of neonatal RBC may facilitate blood flow in narrow vessels, particularly in vessels with high osmolality (i.e. renal vasa recta). © 1993 International Pediatric Research Foundation, Inc.