Extent of intravital contraction of arterial and venous thrombi and pulmonary emboli.

Blood clots and thrombi undergo platelet-driven contraction/retraction followed by structural rearrangements. We have established quantitative relationships between the composition of blood clots and extent of contraction to determine intravital contraction of thrombi and emboli based on their content. The composition of human blood clots and thrombi was quantified using histology and scanning electron microscopy. Contracting blood clots were segregated into the gradually shrinking outer layer that contains a fibrin-platelet mesh and the expanding inner portion with compacted red blood cells (RBCs). At 10% contraction, biconcave RBCs were partially compressed into polyhedral RBCs, which became dominant at 20% contraction and higher. The polyhedral/biconcave RBC ratio and the extent of contraction displayed an exponential relationship, which was used to determine the extent of intravital contraction of ex vivo thrombi, ranging from 30% to 50%. In venous thrombi, the extent of contraction decreased gradually from the older (head) to the younger (body, tail) parts. In pulmonary emboli, the extent of contraction was significantly lower than in the venous head but was similar to the body and tail, suggesting that the emboli originate from the younger portion(s) of venous thrombi. The extent of contraction in arterial cerebral thrombi was significantly higher than in the younger parts of venous thrombi (body, tail) and pulmonary emboli but was indistinguishable from the older part (head). A novel tool, named the "contraction ruler," has been developed to use the composition of ex vivo thrombi to assess the extent of their intravital contraction, which contributes to the pathophysiology of thromboembolism.