EFFECT OF A STABILIZED MICROBUBBLE ECHO CONTRAST AGENT ON HEMOLYSIS OF HUMAN ERYTHROCYTES EXPOSED TO HIGH-INTENSITY PULSED ULTRASOUND

Microbubble contrast agents have been shown to enhance ultrasonic cell lysis in vitro when exposed to continuous-wave ultrasound having spat ial peak temporal average (SPTA) intensities of a few W/cm2. The respo nse is strongly dependent upon the hematocrit (HCT) of the cell sample ; detectable cell lysis essentially disappears as the HCT approaches 5 %-10%. This study was conducted to determine whether high intensity pu lsed ultrasound is an effective lytic agent in the presence of preexis ting potential cavitation nuclei (Albunex(R) contrast agent). Human er ythrocytes were suspended in autologous plasma to HCTs ranging from 1% -40%. Suspensions were exposed or sham exposed for 60 seconds to focus ed, pulsed ultrasound. The pulse duration was 1 msec, and the pulse re petition frequency was 20 Hz. The pressure amplitudes, spatial peak pu lse average (SPPA) intensity, and SPTA intensity were 4.7 MPa peak pos itive pressure, -2.7 MPa peak negative pressure, 420 W/cm2, and 8.5 W/ cm2, respectively. Samples were exposed to ultrasound in a dialysis me mbrane exposure vessel rotating at 200 rpm. When included in the eryth rocyte samples, the Albunex concentration was 35 muL/mL suspension. Si gnificant ultrasound-induced hemolysis in the absence of Albunex was o bserved only at the lowest HCT value tested (1%). In the presence of A lbunex significant cell lysis was observed at all tested HCT values. T he relative fraction of cells lysed by the combination of ultrasound e xposure and Albunex diminished with increasing HCT, but the number of cells lysed per sample was nearly constant over the range of 5%-40% HC T. The ultrasound exposure parameters used in this study differ substa ntially from those associated with diagnostic imaging equipment; it is not valid to infer from the present results that the use of Albunex i n diagnostic applications will induce or enhance hemolysis in vivo.