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P3. Rheology of blood coagulation
Plenary Sessions
102 P3.
RHEOLOGY
OF BLOOD
Vol. 32, Nos. 2-3
COAGULATION
M. KAIBARA Biopolymer Physics Laboratory, The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan Although the blood coagulation process is very complicated, coagulation is essentially the polymerization and network formation of fibrin by the catalytic action of thrombin. The network structure of fibrin clots formed u n d e r different conditions is discussed from the kinetic analysis of the change of dynamic rigidity modulus during coagulation. Formation of covalent crosslinks between fibrin molecules, platelet function and fibrinolysis significantly affect the rigidity of the clot. The rheological methods are important for investigating the coagulation mechanism of blood and the dynamic process of fibrinolysis, and may also be used for monitoring drug efficacy in therapies as well as for diagnosis of thrombosis. In addition, rheological techniques make it possible to analyze the initial coagulation reaction in contact with vascular vessel components such as endothelial cells, smooth muscle cells or collagen as well as artificial vascular vessels. Using a measuring system consisting of a damped oscillation r h e o m e t e r and endothelial cell-coated tube, the coagulation reaction due to the interactions between coagulation factors and blood cells has been studied. It is shown that the intrinsic coagulation reaction is promoted on the erythrocyte surface. P4.
RHEOLOGY
OF LIVING SOFT TISSUES
Y. C. FUNG Department of Bioengineering, and Center for Biomedical Engineering, University of California, San Diego, LaJolla, CA 92093-0412, USA Recent studies of tissue remodeling make us sensitive to the fact that the zero-stress state of a tissue and its rheological properties change with the biological process. Case after case, it was found that the change of tissue rheology is quite rapid. Since rheology is described by the stress-strain-history relationship of the tissue, the identification of the zero-stress state, relative to which the stress and strain are measured, is very important. Fortunately, for some organs the identification is easy. For example, if we cut a blood vessel into segments, and then cut these segments radially, they will open up into sectors which are in zero-stress state. For an aortic arch, it will open up into sectors which are ahnost flat. For the pulmonary artery in the arch region, the vessel will turn itself inside out. The opening angle of the sector, defined by the angle between two radii originating at the mid-point of the endothelium to the tips of the endothelium, changes in the course of remodeling u n d e r hypertension. In the meantime, the rheological properties of the blood vessel are also remodeled. If the rheological remodeling is caused by a step increase of blood pressure, then the parameters of the rheological properties can be expressed as indicial functions of time. A full set of indicial functions is required to define the rheological properties of the tissue. A review of the current state of knowledge about the nonlinear stress-su-ain law, the continuous relaxation spectrum of the rheological behavior, and the indicial functions of soft tissue remodeling under step changes of stress will be presented.
102 P3.
RHEOLOGY
OF BLOOD
Vol. 32, Nos. 2-3
COAGULATION
M. KAIBARA Biopolymer Physics Laboratory, The Institute of Physical and Chemical Research (RIKEN), Wako, Saitama 351-01, Japan Although the blood coagulation process is very complicated, coagulation is essentially the polymerization and network formation of fibrin by the catalytic action of thrombin. The network structure of fibrin clots formed u n d e r different conditions is discussed from the kinetic analysis of the change of dynamic rigidity modulus during coagulation. Formation of covalent crosslinks between fibrin molecules, platelet function and fibrinolysis significantly affect the rigidity of the clot. The rheological methods are important for investigating the coagulation mechanism of blood and the dynamic process of fibrinolysis, and may also be used for monitoring drug efficacy in therapies as well as for diagnosis of thrombosis. In addition, rheological techniques make it possible to analyze the initial coagulation reaction in contact with vascular vessel components such as endothelial cells, smooth muscle cells or collagen as well as artificial vascular vessels. Using a measuring system consisting of a damped oscillation r h e o m e t e r and endothelial cell-coated tube, the coagulation reaction due to the interactions between coagulation factors and blood cells has been studied. It is shown that the intrinsic coagulation reaction is promoted on the erythrocyte surface. P4.
RHEOLOGY
OF LIVING SOFT TISSUES
Y. C. FUNG Department of Bioengineering, and Center for Biomedical Engineering, University of California, San Diego, LaJolla, CA 92093-0412, USA Recent studies of tissue remodeling make us sensitive to the fact that the zero-stress state of a tissue and its rheological properties change with the biological process. Case after case, it was found that the change of tissue rheology is quite rapid. Since rheology is described by the stress-strain-history relationship of the tissue, the identification of the zero-stress state, relative to which the stress and strain are measured, is very important. Fortunately, for some organs the identification is easy. For example, if we cut a blood vessel into segments, and then cut these segments radially, they will open up into sectors which are in zero-stress state. For an aortic arch, it will open up into sectors which are ahnost flat. For the pulmonary artery in the arch region, the vessel will turn itself inside out. The opening angle of the sector, defined by the angle between two radii originating at the mid-point of the endothelium to the tips of the endothelium, changes in the course of remodeling u n d e r hypertension. In the meantime, the rheological properties of the blood vessel are also remodeled. If the rheological remodeling is caused by a step increase of blood pressure, then the parameters of the rheological properties can be expressed as indicial functions of time. A full set of indicial functions is required to define the rheological properties of the tissue. A review of the current state of knowledge about the nonlinear stress-su-ain law, the continuous relaxation spectrum of the rheological behavior, and the indicial functions of soft tissue remodeling under step changes of stress will be presented.