Vincent T. Turitto

Rheological Factors Influencing Platelet Interaction with Vessel Surfaces

An in vitro perfusion system was used to investigate platelet interaction with subendothelium from rabbit aorta exposed to blood under controlled flow conditions. A morphological technique was used to measure platelet adhesion and thrombus formation. Classical mass transport theory modified to account for the dependence of platelet diffusivity on wall shear rate was used to analyze the results. Platelet adhesion increased with wall shear rate (10–650 sec−1), red cell concentration (10–70%), and platelet concentration (50–300 nl−1) and decreased with axial distance (0–20 mm) from the leading edge. Under these flow conditions platelet adhesion rate was determined predominantly by diffusional transport of platelets to the vessel surface. As shear rate increased to 10,000 sec−1, a transition from diffusion to a more kinetic rate limiting adhesion was observed. Few thrombi were observed at low values of platelet concentration (<150/ml), red cell concentration (<25%), or wall shear rate (<200 sec−1). The format...

The role of convection and diffusion on platelet adhesion and aggregation.

The reactions among clotting components, among platelets, and between these groups are complex biochemical phenomena that importantly affect thrombogenesis, but thrombogenesis is also affected by the physical phenomena of convection and diffusion, which, in turn, are importantly mediated by conditions of flow. The principles that govern convection and diffusion processes are generally well understood, but the significance of these processes in thrombogenesis is in only the early stages of demonstration.

INTERACTION OF PLATELETS WITH SUBENDOTHELIUM: A NEW METHOD FOR IDENTIFYING AND CLASSIFYING ABNORMALITIES OF PLATELET FUNCTION*

Platelets are thought to contribute to hemostasis by adhering to elements of the vessel wall and by forming aggregates that result in the arrest of bleeding. Because of the difficulty of quantifying platelet reactivity in vivo, a variety of in vitro tests have been developed for the study of platelet function. Among these are measurements of platelet retention in glass bead filters, the aggregation of platelets by various agents in an instrument known as an aggregometer, clot retraction, and the development of platelet procoagulant (platelet factor 3 activity). With these tests, a variety of defects in platelet function have been identified in patients with bleeding disorders (FIGURE 1 ) .l It is tempting to assume that some abnormality of platelet function during the primary arrest of bleeding accounts for the hemostatic defects in these patients. Direct evidence, however, concerning the interaction of platelets with vascular surfaces in these subjects has been lacking. Baumgartner has recently developed a technique for directly assessing the adhesion and aggregation of platelets in citrated whole blood with the subendothelium of rabbit aortic segments under flow conditions similar to those in arteries2We have used this technique to study plateletsubendothelium interaction in a variety of hemostatic disorders and have found abnormalities in adhesion or aggregation that may account for the hemostatic defects in these In this paper, we shall review the results of these previously published studies and present some more recent observations on the interaction of platelets with the subendothelium.