Effect of 40-kHz ultrasound on acute thrombotic ischemia in a rabbit femoral artery thrombosis model - Enhancement of thrombolysis and improvement in capillary muscle perfusion

Background - We have shown previously that 40-kHz ultrasound (US) at low intensity accelerates fibrinolysis in vitro with little heating and good tissue penetration. These studies have now been extended to examine the effects of 40-kHz US on thrombolysis and tissue perfusion in a rabbit model. Methods and Results - Treatment was administered with either US alone at 0.75 W/cm(2), streptokinase alone, or the combination of US and streptokinase. US or streptokinase resulted in minimal thrombolysis, but reperfusion was nearly complete with the combination after 120 minutes. US also reversed the ischemia in nonperfused muscle in the absence of arterial flow. Tissue perfusion decreased after thrombosis from 13.7+/-0.2 to 6.6+/-0.8 U and then declined further to 4.5+/-0.4 U after 240 minutes. US improved perfusion to 10.6+/-0.5 and 12.1+/-0.5 U after 30 and 60 minutes, respectively. This effect was reversible and declined to pretreatment values after US was discontinued. Similarly, tissue pH declined from normal to 7.05+/-0.02 after thrombosis, but US improved pH to 7.34+/-0.03 after 60 minutes. US-induced improvement in tissue perfusion and pH also occurred after femoral artery ligation, indicating that thrombolysis did not cause these effects. Conclusions - 40-kHz US at low intensity markedly accelerates fibrinolysis and also improves tissue perfusion and reverses acidosis, effects that would be beneficial in treatment of acute thrombosis.