Viscosity reduction of red blood cells from preterm and full-term neonates and adults in narrow tubes (Fahraeus-Lindqvist effect).

In artificial tubes as well as in blood vessels with diameters less than 500 microns, blood viscosity decreases with decreasing diameter (Fahraeus-Lindqvist effect). Our study measured viscosity of red blood cells (RBC) from 10 preterm infants, 10 term neonates, and 10 adults by means of a capillary viscometer. RBC were suspended in buffer at hematocrits of 0.20, 0.40, and 0.60 1/1 (1.00 1/1 = 100%). Tubes with diameters of 50, 100, and 500 microns were perfused with these suspensions. Viscosity in the 500-microns tubes was not significantly different, at any hematocrit, among the three groups. Viscosity decreased at each of the adjusted hematocrits in the three groups when going from a 500-microns tube to a 50-microns tube. At a hematocrit of 0.60 1/1, viscosity reduction averaged 48 +/- 7% in the preterm infants, 42 +/- 8% in the full-term neonates, and 35 +/- 5% in the adults, whereas the reductions at a hematocrit of 0.20 1/1 were only 32 +/- 6, 27 +/- 4, and 24 +/- 6%, respectively. For the combined data from the neonates and adults, there was a significant inverse relationship of the viscosity in 50-microns tubes at a hematocrit of 0.60 1/1 to the mean corpuscular volume (r = 0.69). To evaluate whether increased membrane elasticity of neonatal RBC contributes to the stronger viscosity reduction of neonatal RBC in narrow tubes, heated neonatal and adult RBC were also studied. The resulting loss of membrane elasticity caused a marked decrease in the viscosity reduction in 50-microns tubes, particularly in the neonates.(ABSTRACT TRUNCATED AT 250 WORDS)