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F114. Red cell motion in diverging capillary bifurcations: Effect of shape on hematocrit distribution
284
Free Communications
Vol. 32, Nos. 2-3
FlI4. R E D CEIJ. M O T I O N I N D I V E R G I N G C A P I I J A R Y BIFURCATIONS: EFFECT OF SHAPE ON HEMATOCRIT DISTRIBUTION A. W. EL-KAREH AND T. W. SECOMB Department of Physiology, University of Arizona, Tucson AZ 85724 USA Unequal hematocrit distribution between the two downstream vessels of a diverging capillary bifurcation results from two factors: uneven red cell distribution in the upstream vessel, and deviation of red cell trajectories from fluid streamlines. This study focuses on the latter effect, which is more important for smaller vessels. The bifurcation is modeled by flow impinging on a cylindrical post between two parallel plates, with the red cells represented as spherical caps. Trajectories for various initial orientations are computed for caps of varying degrees of flatness. Both symmetrically and asymmetrically divided flows are examined. Computed trajectories show that spherical caps of different orientations, all starting on the same fluid dividing streamline several radii upstream of the dividing surface, deviate slightly to one side or the other, and this ultimately affects which branch they follow. When the flow is asymmetric, the net result is a migration of caps to one side, even if their upstream distribution is uniform and there is no preferred upstream orientation. The cap orientation may be changed by a shear component in the flow, and by wall interactions. Little rotation is seen until interaction with the dividing surface is strong. As the caps near the dividing surface, rotation tends to orient their axes perpendicular to the wall. This reorientation as the caps pass near the dividing surface influences the distribution of orientations in the downstream branches, which affects cell distribution in s u b s e q u e n t bifurcations. Supported by NIH grants HL34555 and HL07249.
L U M I N A L D I S T R I B U T I O N O F RED B L O O D C E L L S (RBC) AND RBC VELOCITY NEAR ARTERIOLAR B I F U R C A T I O N S IN H A M S T E R R E T R A C T O R M U S C L E Fl15.
A. A. PARTHASARATHI AND R. N. PITI'MAN Departments of Biomedical Engineering and Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298-0551, USA The spatial distribution of RBCs and their velocity were measured by a new video technique. RBCs from Golden hamsters were labeled with fluorescein isothiocyanate and injected, at a labelled fraction of 0.5-1.0%, to give 1-2 labeled RBCs per video frame. Multiple images of individual RBCs in single video frames were obtained by using an external shuttering feature of the intensified CCD video camera. Single RBCs could be tracked for several frames (distance of about 200 lam) in order to obtain their trajectories and velocities at 10-15 lam intervals. Data were accumulated to produce spatial distributions of cell position and velocity at selected axial locations. For a single RBC, velocity varied considerably as the cell moved radially along its 200 lam axial trajectory (e.g., 1.7-2.8 mm/sec; diameter=63 ~tm). The spatial distribution of RBCs did not exhibit any significant asymmetry about the centerline of the vessel. Also, the shape of the velocity distribution became
Free Communications
Vol. 32, Nos. 2-3
FlI4. R E D CEIJ. M O T I O N I N D I V E R G I N G C A P I I J A R Y BIFURCATIONS: EFFECT OF SHAPE ON HEMATOCRIT DISTRIBUTION A. W. EL-KAREH AND T. W. SECOMB Department of Physiology, University of Arizona, Tucson AZ 85724 USA Unequal hematocrit distribution between the two downstream vessels of a diverging capillary bifurcation results from two factors: uneven red cell distribution in the upstream vessel, and deviation of red cell trajectories from fluid streamlines. This study focuses on the latter effect, which is more important for smaller vessels. The bifurcation is modeled by flow impinging on a cylindrical post between two parallel plates, with the red cells represented as spherical caps. Trajectories for various initial orientations are computed for caps of varying degrees of flatness. Both symmetrically and asymmetrically divided flows are examined. Computed trajectories show that spherical caps of different orientations, all starting on the same fluid dividing streamline several radii upstream of the dividing surface, deviate slightly to one side or the other, and this ultimately affects which branch they follow. When the flow is asymmetric, the net result is a migration of caps to one side, even if their upstream distribution is uniform and there is no preferred upstream orientation. The cap orientation may be changed by a shear component in the flow, and by wall interactions. Little rotation is seen until interaction with the dividing surface is strong. As the caps near the dividing surface, rotation tends to orient their axes perpendicular to the wall. This reorientation as the caps pass near the dividing surface influences the distribution of orientations in the downstream branches, which affects cell distribution in s u b s e q u e n t bifurcations. Supported by NIH grants HL34555 and HL07249.
L U M I N A L D I S T R I B U T I O N O F RED B L O O D C E L L S (RBC) AND RBC VELOCITY NEAR ARTERIOLAR B I F U R C A T I O N S IN H A M S T E R R E T R A C T O R M U S C L E Fl15.
A. A. PARTHASARATHI AND R. N. PITI'MAN Departments of Biomedical Engineering and Physiology, Medical College of Virginia, Virginia Commonwealth University, Richmond, VA 23298-0551, USA The spatial distribution of RBCs and their velocity were measured by a new video technique. RBCs from Golden hamsters were labeled with fluorescein isothiocyanate and injected, at a labelled fraction of 0.5-1.0%, to give 1-2 labeled RBCs per video frame. Multiple images of individual RBCs in single video frames were obtained by using an external shuttering feature of the intensified CCD video camera. Single RBCs could be tracked for several frames (distance of about 200 lam) in order to obtain their trajectories and velocities at 10-15 lam intervals. Data were accumulated to produce spatial distributions of cell position and velocity at selected axial locations. For a single RBC, velocity varied considerably as the cell moved radially along its 200 lam axial trajectory (e.g., 1.7-2.8 mm/sec; diameter=63 ~tm). The spatial distribution of RBCs did not exhibit any significant asymmetry about the centerline of the vessel. Also, the shape of the velocity distribution became