Abstract 178

Aim of the study was to investigate the effects of acidosis on rheological parameters of neonatal red blood cells (RBC).

Subjects: Placental blood from 10 healthy term infants was studied. RBC suspensions in phosphate buffer solutions where prepared at different pH values ranging from 7.4 to 6.6 (increments of 0.2). MCV was determined in a Du Pont analyzer. Whole cell deformability was determined in a Myrenne Rheodyn. Viscosities were determined by the means of capillary viscosimetry (280, 100 and 50 µm tubes) at adjusted haematocrits of 0.50 L/L.

Results: MCV increased significantly with decreasing pH values ≤ 7.0 due to swelling (MCV = 114 fl at pH = 6.6; MCV = 103 fl at pH = 7.4). In parallel whole cell deformability decreased by about 26 % (pH = 6.6 compared with pH = 7.4). Viscosities decreased significantly with tube diameter (Fahræus - Lindqvist effect {FLE}) in all of the different pH incubations. There was no difference in viscosities in 280 µm tubes at different pH values. FLE (280 µm vs. 50 µm tube), however, was significantly deminished at pH < 7.0 (37% viscosity reduction at pH = 7.4, 23% viscosity reduction at pH = 6.6), that means viscosity in 50 µm tubes was increased by about 22% at a pH =6.6.

Conclusion: Aside of mechanisms directly affecting the cardiovascular system, unfavourable changes of rheological parameters may contribute to circulatory compromise of neonates with profound perinatal acidosis.