Fluid phase coagulation events have minimal impact on plasma fibrin structure

At high heparin concentrations, protamine concentrations which reverse heparin anticoagulant effects are insufficient to reverse heparin anti-platelet effects

Combined effects of heparin and protamine on plasma clot structure and platelet function were studied. Anticoagulant effects were monitored as changes in aPTT. Clot structure was defined in terms of fibrin fiber mass/length ratio (mu) and clot elastic modulus (EM). Platelet function was studied utilizing platelet aggregation and platelet force development (PFD) measurements. Heparin (1 U/ml) prolonged the aPTT from 30 to > 300 seconds, reduced PFD from 5,100 to 0 dynes, decreased mu (in batroxobin-induced gels) from 1.36 to 1.08 x 10(13) daltons/cm and decreased clot EM from 9,600 to 2000 dynes/cm2. Varying amounts of protamine reversed these effects: 16 micrograms/ml normalized the aPTT, 20 micrograms/ml normalized PFD, 32 micrograms/ml corrected mu, and 20 micrograms/ml returned EM to baseline. At high heparin concentrations (4 U/ml), protamine concentrations which corrected anticoagulant effects were inadequate to reverse antiplatelet effects. A protamine concentration of 40 micrograms/ml normalized the aPTT and mu, but 140 micrograms/ml of protamine was required to reverse heparin suppression of force development and clot elastic modulus. Excess protamine inhibited clotting and platelet function. In plasma containing 1 u heparin/ml, 140 micrograms protamine/ml reduced PFD by 83%, prolonged the aPTT by 63%, and reduced clot EM by 75%. In heparin free plasma, > 75 micrograms protamine/ml prolonged the aPTT. Thus, platelet function and clot structure are sensitive to protamine during heparin neutralization, and anti-platelet effects of heparin may persist when the aPTT is completely corrected. Excess protamine inhibits platelet function and compromises clot structure.

Calculation of plasma fibrin fiber mass-length ratios utilizing platelet aggregometers

We report a technique for measuring plasma gel fiber size utilizing optical platelet aggregometers. Three aggregometers were used to measure gelation kinetics and final gel turbidity: Sienco Model DP247E, Bio-Data Model PAP-2A, and Chrono-log Model 500-VS aggregometer. Each aggregometer was calibrated using dilutions of latex microspheres. Optical densities of microsphere solutions were measured at 626, 670 and 945 nm. Calibration curves were plots of aggregometer readings versus absorbance. Gels of various fiber size were prepared by varying thrombin concentrations and ionic strength. Fiber mass-length ratios were calculated from the wavelength dependence of gel turbidity. Gel optical densities at 640 nm and 945 nm were shown to be linear functions of fiber mass-length ratio. Aggregometer study gels were formed directly in aggregometer cuvettes. Gel formation kinetics were easily measured in the Sienco and Chrono-log instruments. Gelation kinetics in the Bio-Data instrument did not allow measurement of maximum turbidity. The latter value could be measured, however, once gelation was complete. Final aggregometer readings were made one hour after thrombin addition, and were converted to absorbance values using calibration curves. Absorbencies were then converted to mass-length ratios using the optical density versus mass-length ratio plots. Fiber mass-length ratios measured with aggregometers were in good agreement with those measured spectrophotometrically. This technique may allow routine quantification of plasma clot structure utilizing equipment ordinarily available in clinical laboratories.