Effect of SW rate on stone fragmentation in vivo

Abstract

The trend toward ungated SWL means that SW’s are often delivered at a fast rate (≥2 Hz). This is a concern, since rapid SW delivery causes increased renal injury in experimental animals. Also, in vitro studies show that slowing the SW rate (<2 Hz) improves stone fragmentation. In the current study, the effect of SW rate on stone comminution was tested in an in vivo model. Gypsum stones were inserted into both kidneys of 100 lb pigs via percutaneous access. SWL was performed (Dornier HM3, 400 SW’s uninterrupted, 20 kV, 2 Hz or 0.5 Hz), and stone fragments were collected and sieved through 2 mm mesh. The percent of stone weight lost (particles <2 mm), was greater in stones shocked at the slower rate, 55.1±4.9<th>% (n=6), compared to the faster rate, 19.4±5.6<th>% (n=6) [p<0.0008]. These data indicate that slowing the SW rate improves the efficiency of stone fragmentation in vivo. It is observed in vitro that bubbles along the SW axis are more numerous with faster SW rate; this could impose a barrier to transmission of SW energy into the stone. Localization of the site of rate-dependent bubble activity could provide clues to help improve SWL. [Work supported by NIH Grant P01 DK43881.]