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

Background - We have shown previously that 40-kHz ultrasound (US) at low in tensity accelerates fibrinolysis in vitro with little heating and good tiss ue 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 t he ischemia in nonperfused muscle in the absence of arterial flow. Tissue p erfusion 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 t o 10.6+/-0.5 and 12.1+/-0.5 U after 30 and 60 minutes, respectively. This e ffect was reversible and declined to pretreatment values after US was disco ntinued. Similarly, tissue pH declined from normal to 7.05+/-0.02 after thr ombosis, but US improved pH to 7.34+/-0.03 after 60 minutes. US-induced imp rovement in tissue perfusion and pH also occurred after femoral artery liga tion, 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 woul d be beneficial in treatment of acute thrombosis.