Effect of macroscopic air bubbles on cell lysis by shock wave lithotripsy in vitro

In studies of cells or stones in vitro, the material to be exposed to shock waves (SWs) is commonly contained in plastic vials. It is difficult to rem ove all air bubbles from such vials. Because SWs reflect at an air-fluid in terface, and because existing gas bubbles can serve as nuclei for cavitatio n events, we sought to determine in our system whether the inclusion of sma ll, visible bubbles in the specimen vial has an effect on SW-induced cell l ysis. We found that even small bubbles led to increased lysis of red blood cells (1- to 3-mm diameter bubbles, 9.8 +/- 0.5% lysis, n = 7; no bubbles, 4.4 +/- 0.8%, n = 4), and that the degree of lysis increased with bubble si ze. Damage could not be reduced by centrifuging the cells to the opposite e nd of the vial, away from the bubble. B-scan ultrasound imaging of blood in polypropylene pipette bulbs showed that, with each SW, bubbles were recrui ted from the air interface, mixing throughout the fluid volume, and these a ppeared to serve as nuclei for increased echogenicity during impact by subs equent SWs; thus, bubble effects in vials could involve the proliferation o f cavitation nuclei from existing bubbles. Whereas injury to red blood cell s was greatly increased by the presence of bubbles in vials, lytic injury t o cultured epithelial cells (LLC-PK1, which have a more complex cytoarchite cture than red blood cells) was not increased by the presence of small air bubbles. This suggests different susceptibility to SW damage for different types of cells. Thus, the presence of even a small air bubble can increase SW-induced cell damage, perhaps by increasing the number of cavitation nucl ei throughout the vial, but this effect is variable with cell type. (C) 199 9 World Federation for Ultrasound in Medicine & Biology.