The effect of 40 kHz ultrasound on tissue plasminogen activator-induced clot lysis in three in vitro models.

In a previous study, high-frequency ultrasound (US) (3 MHz) was shown to enhance in vitro fibrinolysis through enhanced supply of plasminogen to the clot surface. The application of high-frequency US is limited in vivo, however, due to tissue heating. We continued our research using low-frequency US with less tissue heating and improved penetration of the US. Three different in vitro models, internal plasma clot lysis and external lysis with compacted and noncompacted plasma clots, were used to determine the magnitude of the effect of low-frequency US (40 kHz; 0.5 W/cm(2)) on tissue plasminogen activator-induced lysis and to elucidate the mechanisms behind the effect. US enhanced lysis in all three models, with the largest effects (fourfold) being in the compacted plasminogen-poor clot model. Plasminogen supply to the clot surface was again shown to be an important contributor to US-enhanced lysis.