Compaction stasis due to gravitational red cell migration and floatational plasma skimming. Reversal of the fahraeus effect due to pathological RCA-formation in plastic tubes and mesenteric venules.

A horizontally aimed microscope was directed at isolated rat mesentery preparations as well as artificial microchannels cast in polyester blocks. They were perfused with aggregating red cell suspensions containing about 7 g/l of bovine fibrinogen at various perfusion pressures. The effects induced by gravitational influences were monitored by measuring the local red cell concentration (video-densitometry) and velocity profiles (IPM-dual slit velocimetry). At low perfusion pressures, sedimentation during maintained flow occurs, leading to a relative red cell slowing compared with plasma. Consequently, a progressive deposition of red cells at the bottom of vessels occurs and finally, blocking of the vessel by aggregated red cells is seen. Thus, the well-known phenomenon of compaction stasis must be attributed not merely to a transmural plasma loss but also to gravitationally induced haemoconcentration.