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20. Blood Rheology and the Microcirculation 

Blood rheology

• Definitions of rheologic parameters (shear stress, shear rate, viscosity, Newtonian fluid, non-Newtonian fluid, yield stress, Hagen-Poiseuille law, Reynold's number).
• Measurement of viscosity (rotating cylindrical viscometers and the cone on plate viscometers).
• Viscosity of plasma.
• Viscoelastic properties of erythrocytes and leukocytes.
• Viscosity of blood.
• Effects of vessel diameter on the viscosity of blood.

Microcirculation

• Topographic features.
• Measurement of microvascular hemodynamics (microvessel pressures, microvessel blood flow).
• Pressure-flow relations in the microcirculation.
• Microvessel hematocrit and apparent viscosity.
• Blood flow through bifurcations or branch points.
• Leukocyte-endothelial cell adhesion.
• Capillary blood flow.
• Effect of red cell concentration on oxygen transport.
• Regulation of blood flow in the microcirculation (local regulation, nervous regulation, humoral and biochemical regulation).
• Capillary-lymphatic dynamics, transport and exchange.

References

Fagrell B, Intaglietta M. Microcirculation: its significance in clinical and molecular medicine. J Intern Med 1997;241:349-362.

This article, written by experts in microcirculation, analyzes the significance of microcirculation in clinical and molecular medicine. The physiology and pathophysiology of this system are reviewed and future directions in the study of microcirculation are outlined.

Usami S. Development of hemorheology: perspective in instrumentation development. Clin Hemorheol Microcirc 2000;23:77-83.

In this article, recent instrumentation developments for the study of hemorheology and molecular biology are reviewed. New viscometers for blood viscometry, improved intravital microscope, fluorescence microscopy, digitized video microscopic techniques as well as laser confocal microscopy are rpesented in terms of recent developments and applications.

Koenig W, Ernst E. The possible role of hemorheology in atherothrombogenesis. Atherosclerosis 1992;94:93-107.

This article reviews the involvement of hemorheological and hemostatic mechanisms in thromboatherogenesis and explores the interactions between these factors and the traditional risk factors for atherosclerosis. elucidation of these mechanisms might lead to new preventive strategies as well as to therapeutic procedures in the management of atherosclerosis and associated thrombotic events.

Stoltz JF, Donner M. New trends in clinical hemorheology: an introduction to the concept of the hemorheological profile. Schweiz Med Wochenschr Suppl 1991;43:41-49.

Blood behaves like a non-Newtonian fluid exhibiting specific features with the probable existence of a plasticity threshold, a viscosity that varies as a function of shear rate and a non-homogeneous nature of the medium during flow. This paper discusses factors affecting blood viscosity and reviews hyperviscosity syndromes ensuing from disorders of these factors.

Carpentier PH. New techniques for clinical assessment of the peripheral microcirculation. Drugs 1999;59:17-22.

This article reviews current methods for clinical investigation of the cutaneous microcirculation. These methods are based mainly on laser Doppler and capillary microscopy and, combined with systems for digital image analysis, they allow quantification of the structure of the microvascular bed (quantitative appraisal of microangiopathies) and function (capillary haemodynamics and exchange).