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Influence of erythrocyte deformation on the microcirculation
P1-23 INFLUENCE OF ERYTHROCYTE DEFORMATION ON THE MICROCIRCULATION Y. Suzuki, N. Tateishi, M. Soutani, T. Taniguchi, N. Maeda Dept. of Physiol., School of Medicine, Ehime Univ., Ehime, Japan Deformation of erythrocytes by shear force is important in passing through capillaries, decreasing blood viscosity and promoting oxygen diffusion from inside to outside of erythrocytes. To examine the effect of the deformability on the flow dynamics of erythrocytes in microvessels, human erythrocytes were treated with diamide, which crosslinks spectrins of membrane cytoskeletal proteins (Biochim. Biophys. Acta 735: 104-112, 1983), and suspended in an isotonic phosphate-lactate Ringer solution containing 2.5 g/dl dextran of MW=40000 and 0.5 g/dl bovine serum albumin. The flow behavior of erythrocytes was observed using a part of isolated microvascular bed of rabbit mesentery (supplied by superior mesenteric artery) and the flow images were recorded on a videotape (J. Biomechanics, in press). (i) Thickness of cell-free layer (measured on the digitized video-images using an image processor: J. Biomechanics, in press) increased with an increase of inner diameter of microvessels, decreasing hematocrit and increasing flow velocity of erythrocytes (determined by a dual-spot cross-correlation technique: Circ. Res. 70: 812-819, 1992). (2) The decrease of erythrocyte deformability with diamide (expressed by the deformation index (DI) determined using a high shear rheoscope with a flash photograph system: Blood 69: 727-734, 1987) reduced significantly the thickness of cell-free layer, because of the inhibited axial accumulation of erythrocytes. (3) Flow resistance of the isolated microvascular bed increased with the decrease of erythrocyte deformability and with the decrease of cell-free layer. In the different hematocrit and erythrocyte deformability, the flow resistance correlated well to the suspension viscosity of erythrocytes at high shear rate (e.g., 150 s- ). (4) Symmetrical (parachute-like) deformation of normal erythrocytes was observed in microvessels less than 13 }~ in inner diameter. The maximum inner diameter for the symmetrical deformation (Dmax: 5-8 >m in length of the deformed cell in flow axis) decreased with decreasing erythrocyte deformability: a good relationship between Dmax a~d DI was obtained, as expressed by an equation, Dmax = 22.3 DI + 1.77 (r = 0.976) at 200 dyn/cm z. In conclusion, (i) erythrocyte deformability has an important role on the flow resistance in microvascular system, (2) cell-free layer may be important for local flow resistance, and (3) symmetrical deformation in microvessels gives a measure of deformability of erythrocytes.
P1-24 INFLUENCE OF ERYTHROCYTE AGGREGATION ON THE MICROCIRCULATION N. Tateishi, M. Soutani, Y. Suzuki, T. Takaku, N. Maeda Dept. of Physiol., School of Medicine, Ehime Univ., Ehime, Japan The acceleration of erythrocyte aggregation forms sludge in microvessels and disturbs blood flow especially in low shear region such as in venules. In the present study, the effect of high molecular weight dextran on the flow dynamics of erythrocytes in microvessels and the flow resistance was examined by using a part of microvascular bed isolated from rabbit mesentery supplied by superior mesenteric artery (J. Biomechanics, in press). Human erythrocytes were suspended in an isotonic phosphate-buffered saline containing 4 g/dl bovine serum albumin, and Dextran T-70 (with the average molecular weight of 70400) was added in various concentrations. The thickness of cell-free layer along the inside wall of microvessels was determined under an inverted microscope using an image processor. The flow velocity of erythrocytes was measured by a dual-spot cross-correlation technique (Circ. Res. 70: 812-819, 1992). The perfusion pressure was monitored with a sensor. The continuity of erythrocyte flow in a microvessel was monitored with a spectrophotometer as light intensity change. The data were subjected to the fast Fourier transform and the distribution of frequency component was analyzed on the basis of the power spectra. (i) The thickness of cell-free layer increased with increasing the concentration of Dextran T70, and the flow resistance in the microvascular bed increased. (2) With increasing the concentration of Dextran T-70, the flow of erythrocytes in single microvessels became intermittent and discontinuous. (3) The flow resistance increased in agreement with the increase of suspension viscosity of erythrocytes at high shear rate. (4) The flow resistance obtained in the presence of Dextran T-70 was plotted on the flow resistance-suspension viscosity (at high shear rate) curve obtained for erythrocyte suspensions of various hematocrits and with different deformability. In conclusion, erythrocyte aggregation probably provides the local flow resistance in the microvascular system, which must be compensated by flow through by-path. The flow resistance in the present system is apparently determined by the suspension viscosity of erythrocytes at high shear rate. The influence of erythrocyte aggregation must be taken into consideration in the stagnant region of blood flow.
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P1-24 INFLUENCE OF ERYTHROCYTE AGGREGATION ON THE MICROCIRCULATION N. Tateishi, M. Soutani, Y. Suzuki, T. Takaku, N. Maeda Dept. of Physiol., School of Medicine, Ehime Univ., Ehime, Japan The acceleration of erythrocyte aggregation forms sludge in microvessels and disturbs blood flow especially in low shear region such as in venules. In the present study, the effect of high molecular weight dextran on the flow dynamics of erythrocytes in microvessels and the flow resistance was examined by using a part of microvascular bed isolated from rabbit mesentery supplied by superior mesenteric artery (J. Biomechanics, in press). Human erythrocytes were suspended in an isotonic phosphate-buffered saline containing 4 g/dl bovine serum albumin, and Dextran T-70 (with the average molecular weight of 70400) was added in various concentrations. The thickness of cell-free layer along the inside wall of microvessels was determined under an inverted microscope using an image processor. The flow velocity of erythrocytes was measured by a dual-spot cross-correlation technique (Circ. Res. 70: 812-819, 1992). The perfusion pressure was monitored with a sensor. The continuity of erythrocyte flow in a microvessel was monitored with a spectrophotometer as light intensity change. The data were subjected to the fast Fourier transform and the distribution of frequency component was analyzed on the basis of the power spectra. (i) The thickness of cell-free layer increased with increasing the concentration of Dextran T70, and the flow resistance in the microvascular bed increased. (2) With increasing the concentration of Dextran T-70, the flow of erythrocytes in single microvessels became intermittent and discontinuous. (3) The flow resistance increased in agreement with the increase of suspension viscosity of erythrocytes at high shear rate. (4) The flow resistance obtained in the presence of Dextran T-70 was plotted on the flow resistance-suspension viscosity (at high shear rate) curve obtained for erythrocyte suspensions of various hematocrits and with different deformability. In conclusion, erythrocyte aggregation probably provides the local flow resistance in the microvascular system, which must be compensated by flow through by-path. The flow resistance in the present system is apparently determined by the suspension viscosity of erythrocytes at high shear rate. The influence of erythrocyte aggregation must be taken into consideration in the stagnant region of blood flow.
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