Dependence of the Rate and Completeness of Fibrin Clot Destruction on the Acoustic Dose and Ultrasound Intensity.

Abstract

The kinetics of fibrin clot destruction under catheter-delivered 32- to 45-kHz ultrasound (US) has been studied at 36°C-38°C in isotonic saline solution. A pseudo-first-order rate constant increased linearly from 0.06/min to 0.57/min with increasing US intensity I0 from 21.6 to 51.2 W/cm2. At I0=4.4 and 11.4 W/cm2, the degree of clot destruction did not exceed 11%-15% regardless of the time of US exposure. Starting from I0=21.6 W/cm2, the maximum achievable level of clot destruction increased linearly with US intensity, reaching 68% at I0=51.2 W/cm2 after 3 min of US exposure. Thus, US intensity is a key parameter determining the maximum achievable level of clot destruction. However, an increase in US intensity above 30 W/cm2 is limited by the intensified negative sonochemical effect on the enzymatic system of hemostasis caused by an increase in inertial cavitation. The best effect can be achieved with ultrasound of a sufficiently high intensity that ensures a large contribution of stable cavitation, generating microstreaming flows, and a minimum contribution of inertial cavitation, generating microjets and shock waves.