Fast response characteristics of red blood cell aggregation.

The present work reports on an important feature of the fast response dynamics of blood flow observed after abrupt changes of the shearing conditions: distinctive peak values in conductance and light reflection/transmission have been observed at short times after the abrupt changes in the shearing conditions and have been attributed to red blood cell (RBC) disorientation and shape changes. Optical shearing microscopy results from the present study show that this peak is directly related to the inter-cellular or inter-aggregate spacing, quantified as the plasma gaps present in the captured images. In order to provide a more in-depth understanding of the structural characteristics of blood subjected to abrupt changes in the flow conditions, normal human blood samples at hematocrits of 45, 35, 25 and 10% were sheared at 100 s(-1) and the shear then suddenly reduced to values decreasing from 60 to 0 s(-1). Results from the present study agree qualitatively and quantitatively with results previously reported in the literature: the hematocrit and the magnitude of the final shear rate affect the magnitude of the peak values. The characteristic peak time was mostly influenced by the cell concentration. It is suggested that aggregation forces may play a part in the process of the fast response structural and spatial rearrangements of RBC.