Fåhraeus and Fåhreaus-Lindqvist effects for neonatal and adult red blood cell suspensions.

In blood vessels with diameters less than 500 microns, both the hematocrit and viscosity decrease with decreasing tube diameter [Fåhraeus effect (FE) and Fåhraeus-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 (HT) and relative viscosity (eta r) in narrow tubes (32 to 145 microns 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-microns 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 eta r were significantly lower (7% on average) for isotonic neonatal RBC compared with adult cells in 32-microns (p < 0.025), 46-microns, and 146-microns 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.(ABSTRACT TRUNCATED AT 250 WORDS)