The Flow of Flexible and Rigid Blood Cells in 100 μm Glass Capillaries

Sickle cell disease causes normally flexible red blood cells to become rigid when oxygen is removed, occasionally forming long sickle shapes. We have been studying the flow of blood drawn into 100 μm diameter glass capillaries by surface tension as a diagnostic for sickle cell disease. The flow of both oxygenated and deoxygenated cells though the horizontal capillaries is well described by the Lucas Washburn (LW) equation over most of the 3 cm capillary length, despite the fact that blood is not a simple fluid and is known to exhibit margination. The flow of the rigid deoxygenated cells is substantially slower than flexible cells, oxy or deoxy. If the LW equation is used to infer an effective viscosity, we find the viscosity of both rigid and flexible cells can be described by a master equation, η=η₀(1+(φ/φ*)^2.38), where φ* is unique to the size and rigidity of the cells. For deoxygenated cells, we also observe the formation of a dense phase that begins immediately behind the advancing meniscus and grows with time. As the dense phase grows, the flow begins to lag behind LW behavior.