Red blood cells (RBC) have special flow properties that play a key role in blood flow, namely their deformability, adherence and to the endothelium and aggregability.
RBC deformability refers to the ability of the cells to adapt their shape to the dynamically changing flow conditions in order to minimize their resistance to flow. RBC adherence to the blood vessel walls (the endothelium) is a potent catalyst of blood vessel occlusion. Normally RBCs do not adhere significantly to EC. However, enhanced RBC adherence has been implicated in pathophysiology relating to RBC abnormalities such as in sickle cell disease, cerebral malaria, diabetes, and thalassemia, and was found to correlate with the occurrence and severity of vaso-occlusion. RBC aggregability refers to RBC ability to form multicellular aggregates. Normally, the blood flow is sufficient for dispersion of the aggregates before entering the capillaries, which is essential for adequate tissue perfusion. However, in pathological situations which are associated with low-flow states or altered RBC properties, larger-than-normal and stronger RBC aggregates may form, which might be resistant to disaggregation by the blood flow.
A number of methods and instruments have been proposed for determination of the different RBC flo-properties, but they are not satisfactory, and none of them provides a facile method for determination of all three flow-properties at the same time.
To meet these needs we have designed and constructed a Computerized Cell Flow-Properties Analyzer (CFA) that enables the monitoring of blood cells directly visualized in a narrow-gap flow-chamber, under controllable flow rates, resembling those in a small blood vessel. Using original algorithms and software, the CFA analyze the dependence of flow-properties on shear stress (flow rate) and their distribution in large RBC population, as occurs in vivo, and provides a list of parameters for comprehensive characterization of all three RBC flow-properties and their deviation from normal values.
The CFA consists of an adaptable narrow-gap flow chamber (from 10 to 200 mm), placed under a microscope, which is connected to a CCD camera. For characterization of RBC adherence, a slide with confluent EC is placed in the flow chamber. The RBC dynamic organization is continuously monitored by direct visualization of the cells in the flow-chamber, under controllable shear stress resembling that in a small blood vessel at 37oC, and their images are transmitted to a computer for analysis of the desired flow property.
