The effects of shear stress on the clottability of fibrinogen in plasma
Peters, Bruce Craig
Hellums, Jesse D.
Master of Science
One problem encountered in the use of circulatoryassist devices has been alterations of the coagulation mechanism. This study was made to determine if one source of this coagulation problem could be due to increased shear stress in the extracorporeal systems. A plasma pool was collected from thirteen donors and lyophilized to provide identical plasma samples for all experimental results. Tests were made with various shear stress and shear exposure times to determine the effects of these variables. A constant shear stress viscometer was used in this examination, and two systems with different surface to volume ratios were available. The surfaces were siliconized before the plasma was introduced to the viscometer. To determine the magnitude of any surface losses, tests were made with radioactive Iodine (I125) labeled fibrinogen. The tests with the xa.l>eXed fibrinogen showed that no loss of fibrinogen occurred due to adhesion to the surface. Studies made with constant time exposures and varying shear stress indicated that clottability does decrease with increased shear stress up to 1 dynes/cm, at which point an apparent minimum clottability occurred. This loss was attributed to conformational changes causing steric interferences with polymerization sites. The minimum was considered to be caused by a maximum in the steric hindrance of the polymerization sites due to conformational changes. Studies done at constant shear stress, varying time indicate that loss of clottability is a function of both exposure time and shear stress. Variation of the surface to volume ratio suggested that the clottability loss is probably surface dependent.