Rheoscopic investigation of red cell deformability in sickle cell anemia.

Adequate erythrocyte deformability is crucial to microvascular function. In sickle cell anemia, a significant fraction of the circulating red cells lose deformability and assume highly abnormal shapes when exposed to low plasma oxygen tension (PO2). The loss of deformability is believed to induce blockage of flow in capillaries with consequent painful crisis or organ infarcts. The deformability of sickle erythrocytes at graded levels of PO2 were investigated in the rheoscope, a viscometric device consisting of transparent counter-rotating cone and plate. Quantitative indices of deformability obtained from still photographs and videotape recordings of cells subjected to shear flow were: fraction of all suspended cells capable of deformation, steady-state elongation, and time course of transient shape recovery following abrupt flow cessation. Suspensions of unfractionated cells were first equilibrated against gas mixtures (O2, N2, CO2) with PO2 = 160, 40 or 20 mm Hg at room temperature and then sheared under the same atmosphere. Results obtained with blood samples from ten pediatric patients being treated at St. Louis Children's Hospital show strong donor-to-donor variations and significant impairment of deformability in the unsickled members of the cell populations relative to normal controls.