Biological mechanisms of acoustically-induced hemostasis

Several mechanisms are postulated to be responsible for acoustically-induced hemostasis. Both mechanical and thermal aspects of ultrasound energy are thought to play a role. Thermal effects may be important when tissue shrinkage is necessary to close a bleeding site. A moderate temperature rise may also accelerate clotting when hypothermia and coagulopathy is present. Tissue welding via collagen restructuring may be promoted via a thermal effect. The mechanical effects of streaming and radiation pressure may assist in stopping the flow of blood out of a wound and, if directed properly, may cause insertion of blood vessel wall material into a breached region to plug the hole, and aid the natural clotting mechanism. Streaming may provide shearing forces on platelets, facilitating their activation for subsequent aggregation and adhesion to the vessel wall. Cavitation may produce tissue disruption that exposes collagen and tissue factors to platelets thus assisting in triggering clotting. These mechanisms are discussed, and supportive evidence given.