Extracorporeal Shock Wave Lithotripsy: Comparison between Stone and No-Stone Animal Models of SWL*

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Abstract
In vitro experimental data have recently documented alterations in shock wave mechanics after striking a calculus. Whether this alteration enhances, reduces, or has any effect on the extent of tissue injury is unknown. In order to determine the possible alterations in the extent of shock wave damage caused by a calculus in situ, we utilized a swine model. Fifteen pigs were randomly divided into three groups. Control animals had a pyelotomy incision without lithotripsy. The No Stone group had a pyelotomy incision with piezoelectric lithotripsy 2 weeks later; the Stone group had a pyelotomy incision with implantation of a 5-mm plaster of paris stone in the renal pelvis and subsequent lithotripsy of the implanted calculus 2 weeks later. Baseline selective renal functional values by creatinine and para-aminohippurate (PAH) clearance were obtained via occlusive balloon ureteral catheters prior to and 1 month after lithotripsy. The animals were sacrificed at 1 month and the kidneys examined for pathologic changes. Despite the presence of a calculus in situ, no significant differences were found between any of the study groups with regard to either the glomerular filtration rate, renal plasma flow, or the area involved in renal scarring (P > 0.05). Our data suggest that the key determinants of the extent of renal injury by lithotripsy are the applied pressure of the shock waves and the size of the focal region and that these factors are not significantly altered by the presence of a calculus within the collecting system.