New Concepts in Shock Wave Lithotripsy
Section snippets
SWL principles
Despite the large number of lithotripters available, all of these devices rely on the same laws of acoustic physics. Shock waves (ie, a special form of sound waves) consisting of a sharp peak in positive pressure followed by a trailing negative wave are generated extracorporeally and passed through the body to fragment stones. The change in density and acoustic impedance from water to calculus results in stone fragmentation [7]. All lithotripters share four main features: (1) an energy source
Mechanisms of stone fragmentation
The mechanisms described for stone comminution include compressive and shear-induced fracture, spallation, and cavitation. As the calculus develops in vivo, it is formed by both crystallization of minerals as well as organic matrix material. This combination forms an inhomogeneous and imperfect material that has natural “defects.” When the shock wave encounters a stone, the force generated in the plane of the shock wave places stress on these imperfections, resulting in compression-induced
Mechanisms of tissue injury
Clinical experience treating patients with SWL has demonstrated that while SWL is generally safe, shock waves have well-recognized acute renal complications. Although clinicians have long recognized the acute effects of SWL, most have believed that there was no long-term sequela to shock wave treatment. Several series with short follow-up have demonstrated conflicting information on the medical complications of SWL [2]. However, a recent study of 630 patients treated in 1985 with the HM3
Lithotripsy advances
Based on our current understanding of cavitation in stone fragmentation as well as the role of cavitation, vasoconstriction, and free radical formation in SWL-induced tissue injury, several groups are investigating ways in which SWL can be clinically effective and safe. This insight has resulted in research focusing on changes to the lithotripter design, changes in treatment strategy, and the addition of medical adjuncts (Table 1). In addition, recent clinical research has focused on improving
Summary
SWL has revolutionized the way in which urologists manage urinary calculi; however, growing evidence suggests that this procedure is not benign and may increase the risk of long-term side effects. Recent research has provided insight into how SWL results in stone comminution, as well as tissue injury. The positive-pressure component of a shock wave causes a stone to crack, while cavitation results in finely passable fragments. However, cavitation in addition to SWL-induced vasoconstriction is a
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