Bleeding abnormal hemostasis

Excessive bleeding and thrombosis may represent altered states of hemostasis. Impaired hemostasis results in spontaneous bleeding stimulated hemostasis results in thrombus formation. The drugs used to arrest abnormal bleeding and to inhibit thrombosis are the subjects of this chapter. 

Hemostasis is the process of blood clot formation at the site of vessel injury. When a blood vessel wall breaks, the hemostatic response must be rapid, localized, and carefully regulated. Abnormal bleeding or a propensity to nonphysiologic thrombosis (i.e., thrombosis not required for hemostatic regulation) may occur when specific elements of these processes are missing or dysfunctional. The elements responsible for normal hemostasis have received extensive review. 

The von Willebrand factor, which is a multimer of a subunit of molecular weight 200,000, can range in molecular weight from 1 X 106 to 2 X 107. It is the portion of factor VIII complex proteins that is necessary for platelet function. Qualitative or quantitative abnormalities of von Willebrand factor cause the bleeding symptoms of von Willebrand s disease (33). Given the importance of this factor in hemostasis, especially at high shear rates (34), it is not surprising that von Willebrand factor has a dominant effect on thrombus formation in our model. 

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