FIBRIN STRUCTURE AND CONCENTRATION ALTER CLOT ELASTIC-MODULUS BUT DO NOT ALTER PLATELET-MEDIATED FORCE DEVELOPMENT

During clot retraction, platelets interact with fibrin resulting in ma rked reduction of clot volume. Altered fibrin structure has been repor ted to affect clot retraction as measured by serum expression. This st udy was performed to test whether such altered retraction was the resu lt of increased resistance to network collapse or due to decreased for ce development by platelets. Altered fibrin structure was documented a s variation of fibre mass/length ratios (FL) and shifts in clot elasti c modulus. The force developed by platelets during clotting was measur ed directly. Increasing the fibrinogen concentration led to thinner fi bre formation (decreased mu), and a linear increase in gel elastic mod ulus. Over a fibrinogen concentration range of 100 to 400 mg/dl, force development was minimally affected. Force development and clot elasti c modulus increased in a linear fashion with increasing platelet conce ntration. Increasing the calcium concentration from 5 to 20 mM caused a 160% increase in fibrin fibre size (mu), and a 52% decline in clot m odulus. Force developed at 1200 s declined by 17%. At 15 mg/ml, dextra n and hydroxyethyl starch (HES) also increased mu, and decreased clot modulus; however, both agents markedly reduced force development. Incr easing ionic strength or the addition of IgG decreased mu and increase d gel elastic modulus. Force development increased modestly with incre ased ionic strength, did not change with addition of IgG in saline and declined with addition of IgG in maltose. This study indicates that f orce development is primarily dependent on platelet function while clo t modulus depends on both fibrin structure and platelet function. The simultaneous measurements of clot modulus and platelet force developme nt may allow detection and differentiation of anticoagulant and antipl atelet effects.