Ascertaining the relationship between acoustic droplet vaporization, inertial cavitation, and hemolysis

Mechanical stress associated with inertial cavitation (IC) can cause hemolysis. The goal of this study was to determine whether hemolysis occurs during acoustic droplet vaporization (ADV) and subsequent microbubble activity. Perfluoropentane droplets were manufactured using an amalgamation protocol, diluted 30-fold in porcine whole blood, and pumped through a flow phantom maintained at 37 °C. Droplets were insonified with a 5 MHz focused transducer (peak negative pressures of 0.25 MPa to 4.25 MPa, pulse length of 40 cycles, and a pulse repetition frequency of 500 Hz). A 128-element array was used to monitor the nucleation of ADV and to record cavitation emissions. Free hemoglobin in the effluents was assayed to detect hemolytic activity. Hemolysis, IC, and ADV were detected at pressures of 2.25 MPa and higher. At 4.25 MPa, 0.38 ± 0.08% hemoglobin was released post-hemolysis. A positive linear relationship was observed between the percent hemoglobin released and IC dose. Due to the concurrence of ADV and IC, it was not possible to determine whether ADV causes hemolysis independent of IC. These findings should be considered when planning studies of biomedical application of ADV. [Work supported in part by an Acoustic Society of America Robert W. Young Award.]