The effects of leukocytes on blood flow in a model skeletal muscle capillary network.

A model of blood flow in a skeletal muscle microvascular network, typical of a rat spinotrapezius muscle, was used to analyze the effects of white blood cells (WBCs) on network resistance and on the pathways followed by WBCs as they transit the network. This model incorporated plugging of vessel entrances by WBCs and the effects of vessel hematocrit, shear rate, and WBCs on blood apparent viscosity. Blood flow and HCT in each vessel and WBC positions were computed at discrete time steps. WBC introduction increased the network resistance 2.98% under normal conditions, and 14.4% above that of plasma alone when WBCs were considered to be suspended in plasma. This resistance increase was predominantly due to WBC plugging at vessel entrances. Comparison of resistance increases to the number of WBC plugs showed an exponential relationship once a threshold value of plugging was reached. Increased WBC plugging resulted from increases in either the feeding concentration of WBCs or the duration of individual plugs. Increased plug duration was the direct result of using alternate WBC deformation models and increasing WBC viscosity. A WBC viscosity range of 45 to 2400 P was used in the model, corresponding to the viscosities reported by various in vivo and in vitro studies. WBC plugging also significantly affected the pathways taken by WBCs. Under normal conditions, WBCs tended to flow through preferred pathways in the distal portions of the network. With increased plugging, WBC flow became more homogeneous. For significant increases in the network resistance to occur, it is essential that the WBC pathways be distributed throughout the network.