Functional and Morphological Changes Associated with Burst Wave Lithotripsy-Treated Pig Kidneys

Abstract

Purpose: Burst wave lithotripsy (BWL) is a new technique for comminution of urinary stones. This technology is noninvasive, has a low positive pressure magnitude, and is thought to produce minor amounts of renal injury. However, little is known about the functional changes related to BWL treatment. In this study, we sought to determine if clinical BWL exposure produces a functional or morphological change in the kidney. Materials and Methods: Twelve female pigs were prepared for renal clearance assessment and served as either sham time controls (6) or were treated with BWL (6). In the treated group, 1 kidney in each pig was exposed to 18,000 pulses at 10 pulses/s with 20 cycles/pulse. Pressure levels related to each pulse were 12 and -7 MPa. Inulin (glomerular filtration rate, GFR) and para-aminohippuric acid (effective renal plasma flow, eRPF) clearance was measured before and 1 hour after treatment. Lesion size analysis was performed to assess the volume of hemorrhagic tissue injury created by each treatment (% FRV). Results: No visible gross hematuria was observed in any of the collected urine samples of the treated kidneys. BWL exposure also did not lead to a change in GFR or eRPF after treatment, nor did it cause a measurable amount of hemorrhage in the tissue. Conclusion: Using the clinical treatment parameters employed in this study, BWL did not cause an acute change in renal function or a hemorrhagic lesion.

Keywords: glomerular filtration rate; renal blood flow; renal pathology; ultrasound.

FIG. 1.

Photograph looking down into a tub from above with a BWL treatment head and ultrasound probe in place. Both the BWL treatment head and ultrasound probe are immersed in degassed water. The plastic tub holds a 1-mil-thick plastic membrane in position and helps contain water. The right flank of the pig is indicated in the picture. The ultrasound gel layer is sandwiched between the membrane and flank of the pig (BWL = BWL treatment head and U = ultrasound probe; the arrow indicates the level of degassed water). BWL = burst wave lithotripsy.

FIG. 2.

Photograph showing the side view of the frame that is holding the tub. Also shown is the scaffolding holding the BWL treatment head and ultrasound probe. The plastic tub holds a 1-mil-thick plastic membrane in position and helps contain water. The right flank of the pig is indicated in the picture. The ultrasound gel layer (which cannot be seen here) is sandwiched between the membrane and flank of the pig.

FIG. 3.

Image of the ultrasound machine screen showing the right kidney. After the right kidney is located, a lower pole calix of that kidney is aligned with the focus of the BWL head before treatment begins (arrows indicate the outline of the kidney on the ultrasound screen).

FIG. 4.

Single MRI scan of the T2-weighted signal of a longitudinal section taken from a BWL-treated kidney. The lower pole is at the bottom of the image. Note the lack of dark regions, sites of hemorrhage, located in the kidney parenchyma of the lower pole. Please compare with images from the study by Handa et al (C = cortex that is dark gray and P = papilla that is light gray).

FIG. 5.

Bar graph of the percent change in GFR and eRPF (from baseline) measured after either sham control treatment or BWL treatment. Also included on the graph are values for 95% confidence intervals. For BWL-treated animals, GFR and eRPF did not change significantly from baseline values in either group and the post-treatment values were not significantly different from post-treatment sham values. N = 6 in each group. GFR = glomerular filtration rate; eRPF = effective renal plasma flow. Color images are available online.

FIG. 6.

Bar graph of hemorrhagic lesion sizes from the sham control and BWL-treated groups. The value for the SWL group (far right, Dornier Compact S, 2500 shock waves, power level = 5, at 120 shock waves/minute) is included for comparison purposes and comes from a previously published study using pigs of the same size. No significant difference was found between the sham control or BWL-treated groups. The lesion produced by SWL is significantly larger than that produced by BWL. N = 5 in the sham control group and N = 6 in both the BWL and SWL groups. *Significantly different from the BWL-treated lesion. SWL = shockwave lithotripsy; NS = not significant. Color images are available online.