ad similar fibrin density and accumulation rates at early times as control subjects. However, there was no secondary burst of fibrin at later times, just a steady accumulation adjacent to platelet aggregates. The fibrin in mild samples was most dense on and near the periphery of platelet aggregates. Electron micrographs of mild hemophilia samples show a starburst pattern of fibrin fibers emanating from platelet aggregates. In moderate FVIII deficiencies, little to no fibrin was observed around platelet aggregates. There was a slight increase 
in the accumulation rate in the first two minutes, after which there was no evidence of further fibrin formation. Electron micrographs confirm that there are few, if any, large fibrin fibers on or near platelet aggregates. Similar to moderate deficiencies, in severe FVIII deficiencies there were little to no fibrin fibers observed. The accumulation of fibrin was modest and generally did not significantly change after the first three minutes of the assay. The overlay between the labeled platelets and the labeled fibrin was almost identical in every case, suggesting that the observed signal is likely platelet bound fibrinogen. There was no evidence of fibrin fibers on or near platelet aggregates by electron microscopy. Platelet adhesion preceded fibrin formation for all normal and patient samples. To test whether platelets are necessary for fibrin fiber formation we ran a set of experiments with normal pooled plasma and FVIII deficient platelet poor plasma at 100 s21. N 5 FVIII Deficiencies and Venous Thrombus Formation We observed no fibrin fibers or accumulation of fluorescence signal above background in either case in the middle of the channel over 5 min. In NPP we did observe fibers in the corners of channels, which is a result of accumulation of coagulation products in the low flow areas near the corners of rectangular channels. No fibers were observed anywhere in the channel with FVIII deficient plasma. Fibrin deposition dynamics as a function of FVIII levels We used three metrics to quantify the dynamics of fibrin formation; the maximum fibrin density, the lag time to 10% of maximum fibrin formation for normal subjects, and the velocity of fibrin accumulation defined as the slope of the line defined by the lag time and the time to maximum fibrin density. Both the maximum fibrin density and deposition velocity were strongly correlated to FVIII levels. The lag time was inversely correlated to FVIII levels, although the dependence was not statistically significant. Clinical phenotype and platelet and fibrin accumulation Fibrin accumulation was supported in mild HA, but it was significantly less than for normal FVIII levels. There was not a significant difference in maximum fibrin density between severe and moderate HA. However, platelet aggregates were significantly larger in moderate HA than severe HA. This result suggests that the 24900262 thrombin BioPQQ concentration was high enough to activate platelets in moderate HA, but not to 7910212 support fibrin formation. Thrombin generation dynamics as a function of FVIII levels A computational model of thrombus formation was used to estimate the effect of FVIII on thrombin generation. Thrombin generation was characterized by the average thrombin concentration within the thrombus and by the cumulative thrombin produced, which includes both the thrombin within the thrombus and the thrombin washed away by the flow. The trends are similar for both, so we focus on the average t
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