IN VITRO MODELS OF MICROCIRCULATION IN THE HUMAN FETUS, NEONATE AND ADULT:

Intravital studies on microcirculation in humans have been limited to superficial structures such as the skin or eye. We have used the lubrication theory to describe blood flow in capillaries with diameters of 3 to 6 μm. According to this model red blood cell (RBC) surface area and volume, plasma viscosity and capillary diameter determine the necessary driving pressure for a given RBC flow velocity, the intracapillary hematocrit and blood viscosity, and the critical capillary diameter for RBC passage. Plasma viscosity determines the friction in the gap between RBC and capillary wall (“lubrication”). Plasma viscosity (tube viscometer), surface area and volume of RBCs and the validity of the model (micropipette system) were studied using blood from 10 adults and cord blood from 10 fetuses (18-22 wk), 20 preterm (24-36 wk) and 10 full-term neonates.