Characteristics of cell‐free layer variation in a 25‐μm tube

To examine the effect of aggregation on the cell‐free layer variation, in vitro experiments were performed by perfusing human red cells through a 25‐μm tube. The level of aggregation was adjusted to physioloigcal and pathological levels seen in humans. In addtion to qunatifing the layer width with its mean, additional information on its periodicity and variation frequency was studied by using the auto‐correlation and power spectral density analysis. Interstingly, the contact frequency between red cells and inner tube wall was significantly reduced in hyper‐aggregating conditions as compared to that in non‐aggregating conditions. This result might be due mainly to the enhancement of the layer formation which impaired the opportunity for red cells to become in contact with the tube wall. In the anaysis of the layer periodicity, relatively small magnitude of the auto‐correlation length (< 6.6 μm) as compared to the diameter of red cell (~8 μm) was found, which may imply that the layer variation exhibits non‐periodicity regardless of red cell aggregation conditions. The power spectral density analysis revealed that the temporal variation of the layer was significantly decreased in hyper‐aggregating conditions than that in non‐aggregating conditions.