Time-dependent rheological behavior of blood at low shear in narrow vertical tubes.
The time-dependent flow behavior of normal human blood after a sudden reduction of wall shear stress from 5,000 mPa to a low level (2-100 mPa) was studied during perfusion of vertical tubes (internal diam 28-101 microns) at constant driving pressures. Immediately after the implementation of low-shear flow conditions the concentration of red blood cells (RBCs) near the tube wall started to decrease, and marginal plasma spaces developed as a result of the assembly of RBC aggregates. This was associated with a time-dependent increase of flow velocity by up to 200% within 300 s, reflecting a reduction of apparent viscosity. These time-dependent changes of flow behavior increased strongly with decreasing wall shear stress and with increasing tube diameter. A correlation between the width of the marginal plasma layer and relative apparent viscosity was obtained for every condition of tube diameter, wall shear stress, and time. Time-dependent changes of blood rheological properties could be relevant in the circulation, where the blood is exposed to rapid and repeated transitions from high-shear flow conditions in the arterial and capillary system to low-shear conditions in the venous system.
Alonso
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Institut für Physiologie, Freie Universität Berlin, Germany.
Pries
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AR
Gaehtgens
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D001783:Blood Flow Velocity; D001790:Blood Physiological Phenomena; D001809:Blood Viscosity; D004903:Erythrocyte Aggregation; D004912:Erythrocytes / Q000502:physiology; D006801:Humans; D012212:Rheology; D013314:Stress, Mechanical; D013997:Time Factors