Platelet aggregate formation in a region of separated blood flow

Microscopic observations of the flow of fresh canine blood in a separated region formed by a step in a polyurethane surface have been made. These observations show the formation of large clumps of freely floating aggregates of platelets. These clumps can easily leave the region and may be representative of disorders occurring in the distal circulation when artificial devices are used in the bloodstream. Measurements of the growth rate of these aggregates are compared with a theoretical analysis of the rate of platelet collisions. Some criteria defining conditions under which such free floating aggregates occur are also suggested.