Shock wave–bubble interaction near soft and rigid boundaries during lithotripsy: numerical analysis by the improved ghost fluid method

Non-spherical bubble collapses near solid boundaries, generating water hammer pressures and shock waves, were recognized as key mechanisms for cavitation erosion. However, there is no agreement on local erosion patterns, and cavitation erosion damage lacks quantitative analysis. In our experiments, five distinct local erosion patterns were identified on aluminium sample surfaces, resulting from the collapse of laser-induced cavitation bubbles at moderate stand-off distances of $0.4\leqslant \gamma \leqslant 2.2$ , namely bipolar, monopolar, annular, solar-halo and central. Among them, the bipolar and monopolar patterns exhibit the most severe cavitation erosion when the toroidal bubbles undergo asymmetrical collapse along the circumferential direction during the second cycle. Shadowgraphy visualization revealed that asymmetrical collapse caused shockwave focusing through head-on collision and oblique superposition of wavefronts. This led to the variations in toroidal bubble radii and the positions of maximum erosion depth not matching at certain stand-off distances. Both initial plasma asymmetry and bubble–wall stand-off distance were critical in determining circumferential asymmetrical collapse behaviours. At large initial aspect ratios, the elliptical jet tips form during the contraction process, resulting in the toroidal bubble collapsing from regions with smaller curvature radii, ultimately converging to the colliding point along the circumferential direction. Our three-dimensional simulations using OpenFOAM successfully reproduce the key features of circumferentially asymmetrical bubble collapse. This study provides new insights into the non-spherical near-wall bubble collapse dynamics and provides a foundation for developing predictive models for cavitation erosion.

The introduction of the cavitation effect in ultrasonic surface rolling can further improve the strengthening effect. However, the mechanism of the time-space bubble collapse in cavitation ultrasonic surface rolling on the material wall is still uncertain. Therefore, in this study, both the shock wave produced by spherical bubble collapse and the microjet generated by non-spherical bubble collapse in cavitation ultrasonic surface rolling were investigated. A dynamic model of spherical bubble collapse in the ultrasonic surface rolling area was established, and the shock wave pressure on the wall surface produced by the collapse was analyzed numerically. The numerical results reveal that the shock wave pressure is significantly influenced by the ultrasonic amplitude. As the ultrasonic amplitude increased from 2 to 5 μm, the maximum collapse pressure of the bubble rose from 4700 to 38690 MPa, while the wall pressure increased from 75.07 to 416.07 MPa. Additionally, the pressure distribution on the wall surface caused by near-wall non-spherical bubble collapse was determined using the computational fluid dynamics (CFD) analysis method. The wall pressure generated by microjets peaked with a slight delay compared to that generated by shock waves, reaching a maximum value of 20.25 MPa when the normalized standoff distance was 0.6. Finally, cavitation erosion experiments were conducted. The results showed that the wall pressure was approximately between 340 and 382 MPa when the amplitude was 5 μm, which is generally consistent with previous numerical calculation results. This indicates that the shock wave generated by the collapse of the spherical bubble plays a dominant role in cavitation ultrasonic surface rolling. These research findings are crucial for further studies on the formation of residual stresses and microstructure evolution in cavitation ultrasonic surface rolling.

The present study deals with the collapse of nonspherical bubbles in a compressible liquid by taking the thermal diffusion into account. The ghost fluid method (GFM) is modified so as to consider the thermal diffusion through the bubble surface. The boundary condition for the temperature continuity at the interface is discussed for determining the values of the ghost fluids. The improved GFM is applied to the collapse of a single spherical bubble. The present results are in good agreement with those obtained from the equation of motion for a single bubble (Keller equation) coupling with the energy equation. The improved multigrid GFM is also applied to the interaction of a gas bubble with a strong shock wave. The non-spherical bubble collapse is simulated successfully by taking the thermal diffusion into account. The thermal boundary layers both inside and outside the bubble are captured with the present method although the thermal boundary layer in liquid is very thin. The bubble collapse due to the incident shock wave accompanies the formation of the liquid jets and shock waves leading to the high temperature field. The influence of thermal diffusion becomes more prominent when the initial bubble radius is small. It is shown that a large amount of heat outflows from the interior of the bubble to the liquid when the liquid jet hits the downstream surface of the bubble and the bubble rebounds. The increased thermal diffusion causes the decrease of the internal pressure and temperature in the bubble leading to more violent collapse.

In vitro study of the mechanical effects of shock-wave lithotripsy

The interaction of air bubbles attached to gelatin surfaces, rat’s livers, or rat’s abdominal aortas with underwater shock waves was investigated to clarify the tissue damage mechanism by cavitation bubbles induced during extracorporeal shock wave lithotripsy. The overpressure of the shock wave was 10.2±0.5 MPa (n=4). The initial bubble radii varied from 0.12– 3.06 mm. The subsequent collapse of the bubbles was recorded by a high-speed framing camera. The liver cell damage was histochemically evaluated. The bubble attached to the gelatin or rat’s liver surface migrates away from the surface with an oscillatory growth/collapse behavior after the shock wave interaction. The penetration depth of the liquid jet into the gelatin and the diameter of the subsequent damage pit on the surface depend on the initial bubble radius. The bubble near the rat’s liver surface or aorta surface tends to show the same behavior as for the gelatin. The elongation and split of the nuclei in the liver parenchyma in the direction of the liquid jet and the increase in the cell density within the circumference of the injured region are histochemically revealed.

ESWL: Past, Present, and Future

Instantaneous streamlines, particle pathlines and pressure contours for a cavitation bubble in the vicinity of a free surface and near a rigid boundary are obtained. During the collapse phase of a bubble near a free surface, the streamlines show the existence of a stagnation point between the bubble and the free surface which occurs at a different location from the point of maximum pressure. This phenomenon exists when the initial distance of the bubble is sufficiently close to the free surface for the bubble and free surface to move in opposite directions during collapse of the bubble. Pressure calculations during the collapse of a cavitation bubble near a rigid boundary show that the maximum pressure is substantially larger than the equivalent Rayleigh bubble of the same volume.

Stones in the urinary tract are a common medical problem in the general population. At present, the great expansion in minimally invasive techniques has led to the decrease in open surgery. Extracorporeal shock wave lithotripsy (ESWL) has been introduced as an alternative approach which disintegrates stones in the kidney and upper urinary tract through the use of shock waves. Nevertheless, as there are limitations with the success rate in ESWL, other minimally invasive modalities for kidney stones such as percutaneous nephrolithotomy (PCNL) and retrograde intrarenal surgery (RIRS) are also widely applied. This is an update of a review first published in 2009. This review aimed to assess the effectiveness and complications of ESWL for kidney stones compared with PCNL or RIRS. We searched the Cochrane Renal Group's Specialised Register to 3 March 2014 through contact with the Trials' Search Co-ordinator using search terms relevant to this review. Randomised controlled trials (RCTs) assessing the use of ESWL compared to PCNL or RIRS for kidney stone management. Two authors independently assessed all the studies for inclusion. Statistical analyses were performed using the random effects model and the results expressed as risk ratio (RR) for dichotomous outcomes or mean difference (MD) for continuous data with 95% confidence intervals (CI). Five studies (338 patients) were included, four studies compared ESWL to PCNL and one compared ESWL with RIRS. Random sequence generation was reported in three studies and unclear in two. Allocation concealment was not reported in any of the included studies. Blinding of participants and investigators could not be undertaken due to the nature of the interventions; blinding of outcome assessors was not reported. Reporting bias was judged to be low risk in all studies. One study was funded by industry and in one study the number of participants in each group was unbalanced.The success of treatment at three months was significantly greater in the PCNL compared to the ESWL group (3 studies, 201 participants: RR 0.46, 95% CI 0.35 to 0.62). Re-treatment (1 study, 122 participants: RR 1.81, 95% CI 0.66 to 4.99) and using auxiliary procedures (2 studies, 184 participants: RR 9.06, 95% CI 1.20 to 68.64) was significantly increased with ESWL group compared to PCNL. The efficiency quotient (EQ; used to assess the effectiveness of procedures) higher for PCNL than ESWL; however EQ decreased when stone size increased. Duration of treatment (MD -36.00 min, 95% CI -54.10 to -17.90) and hospital stay (1 study, 49 participants: MD -3.30 days, 95% CI -5.45 to -1.15) were significantly shorter in the ESWL group. Overall more complications were reported with PCNL, however we were unable to meta-analyse the included studies due to the differing outcomes reported and the timing of the outcome measurements.One study compared ESWL versus RIRS for lower pole kidney stones. The success of treatment was not significantly different at the end of the third month (58 participants: RR 0.91, 95% CI 0.64 to 1.30). Mean procedural time and mean hospital stay was reported to be longer in the RIRS group. Results from five small studies, with low methodological quality, indicated ESWL is less effective for kidney stones than PCNL but not significantly different from RIRS. Hospital stay and duration of treatment was less with ESWL. Larger RCTs with high methodological quality are required to investigate the effectiveness and complications of ESWL for kidney stones compared to PCNL if there is any technological progress in the non-invasive elimination of the residual fragments. Moreover, further research is required for the outcomes of ESWL and RIRS in lower and non-lower pole studies including PCNL versus RIRS.

Background/Aims: Chronic leg ulcers (CLUs) are globally a major cause of morbidity and mortality with increasing prevalence. Their treatment is highly challenging, and many conservative, surgical or advanced therapies have been suggested, but with little overall efficacy. Since the 1980s extracorporal shock wave therapy (ESWT) has gained interest as treatment for specific indications. Here, we report that patients with CLU showed wound healing after ESWT and investigated the underlying molecular mechanisms. Methods: We performed cell proliferation and migration assays, FACS- and Western blot analyses, RT-PCR, and Affymetrix gene expression analyses on human keratinocytes and fibroblasts, and a tube formation assay on human microvascular endothelial cells to assess the impact of shock waves in vitro . In vivo , chronic therapy-refractory leg ulcers were treated with ESWT, and wound healing was assessed. Results: Upon ESWT, we observed morphological changes and increased cell migration of keratinocytes. Cell-cycle regulatory genes were upregulated, and proliferation induced in fibroblasts. This was accompanied by secretion of pro-inflammatory cytokines from keratinocytes, which are known to drive wound healing, and a pro-angiogenic activity of endothelial cells. These observations were transferred “from bench to bedside”, and 60 consecutive patients with 75 CLUs with different pathophysiologies (e.g. venous, mixed arterial-venous, arterial) were treated with ESWT. In this setting, 41% of ESWT-treated CLUs showed complete healing, 16% significant improvement, 35% improvement, and 8% of the ulcers did not respond to ESWT. The induction of healing was independent of patient age, duration or size of the ulcer, and the underlying pathophysiology. Conclusions: The efficacy of ESWT needs to be confirmed in controlled trials to implement ESWT as an adjunct to standard therapy or as a stand-alone treatment. Our results suggest that EWST may advance the treatment of chronic, therapy-refractory ulcers.

The treatment of ureteral lithiasis by extracorporeal shock wave lithotripsy (ESWL) is progressively being abandoned owing to advances in endoscopic lithotripsy. The purpose of this paper is to analyze the causes as to why ESWL is less effective-with a measurable parameter: focal applied energy quotient (FAEQ) that allows us to apply an improvement project in ESWL results for ureteral lithiasis. A prospective observational cohort study with 3-year follow-up and enrollment period was done with three groups of cases. In Group A, 83 cases of ureteral lithiasis were treated by endoscopic lithotripsy using Holmiun:YAG laser. In Group B, 81 cases of ureteral lithiasis were treated by ESWL using Doli-S device (EMSE 220F-XXP). In Group C, 65 cases of ureteral lithiasis were treated by ESWL using Doli-S device (EMSE 220F-XXP) (FAEQ >10). Statistical study and calculation of RR, NNT, Chi-square test, Fisher's exact test, and Student's t test were done. Efficiency quotient (EQ) and focal applied energy quotient [FAEQ = (radioscopy seconds/number of shock waves) × ESWL session J] were analyzed. From the results, the success rate of the treatment using Holmium:YAG laser lithotripsy and ESWL is found to be 94 and 48%, respectively, with a statistically significant difference (p < 0.001). Success rate of endoscopic laser lithotripsy for lumbar ureteral stones was 82% versus 57% of ESWL (p = 0.611). In Group B, FAEQ was 8.12. In Group C, success rate was 93.84% with FAEQ of 10.64%. When we compare results from endoscopic lithotripsy with Holmium:YAG laser in Group B with results from ESWL with FAEQ >10, we do not observe absolute benefit choosing one or the other. In conclusion, the application of ESWL with FAEQ >10, that is, improving radiologic focalization of the calculus and increasing the number of Joules/SW, makes possible a treatment as safe and equally efficient as Holmium:YAG laser lithotripsy in ureteral lithiasis less than 13 mm.

Although extracorporeal shock wave lithotripsy (ESWL) is an important technique, the details of how it works—how shock waves interact with stones to cause disruption—and how to optimize its effect are not known with certainty by practitioners of the art. Three position‐dependent mechanisms of disruption were observed. Position dependence was probably due to focusing of the shock wave by an ellipsoidal reflector. Near the focus, the front surfaces of the test objects were roughed (spalated), probably by collapse of cavitation bubbles caused by passage of the shock wave. Also, midspecimen cleavage was seen, presumably caused by back wall reflection tensile stress. Distal to the focus back wall, spalation occurred, possibly due to tension caused by the expanding shock wave. Sieving fraction observations made of the effect of shock waves on “z brick” show that fragmentation has an approximate first‐order dependence on the number of shocks and a second‐order dependence on the voltage at which the shocks were g...

The purpose of this study was to define factors that have a significant impact on the stone-free rate after ESWL. Methods: A total of 417 patients harboring renal or ureteral stones underwent extracorporeal shock wave lithotripsy (ESWL) between October 2008 and July 2012. Eighty five patients were lost on follow up. The remaining (n = 332). All patients were >18 yr of age. Siemens and SLX-F2 electromagnetic machines were used to impart shock waves. Patients were stratified according to localization (pelvic, calyceal, or ureteral stones) and stone size (up to 10 mm, 10 - 20 mm, and >20 mm). Result: The overall success rate was 251/332 (75.6%) achieve stone free status. Repeated ESWL sessions were needed in 258 (61.9%). Of eleven variables were studied including age, sex, side, location (pelvic, calyx, ureter), ureteric stent, previous renal surgery, stone size, number of shock waves, opacity of stone, renal system state, and type of lithotripter, three variables were significantly affect the success rate namely stone size, number of shock waves and location of stone. Conclusions: ESWL remains one of the most commonly utilized treatments for patients with upper urinary tract calculi; Stone diameter, location, and number of shock waves, are the most important predictors determining stone clearance after ESWL of renal and ureteric calculi. To optimize treatment outcomes with ESWL the presence of treating urologist is essential to optimize the final result.

Cytotoxic Effects of High Energy Shock Waves on Cancer Cells Linked to Metallic Beads Vehicled by Monoclonal Antibodies

1813 EVALUATION OF RISK FACTORS FOR PROGNOSIS OF TEMPORARY RENAL IMPAIRMENT AFTER SECONDARY EXTRACORPORAL SHOCK WAVE LITHOTRIPSY (ESWL) IN RENAL STONE TREATMENT

This study was designed to investigate whether extracorporeal shock wave lithotripsy (ESWL) exposure to parotid gland produces an oxidative stress in parotid glands of rats. Twelve male Wistar-albino rats, 6 months of age with an average body weight of 250-300 g, were divided randomly into two groups, each consisting of six rats. The animals in the first group did not receive any treatment and served as control. The left parotid glands of animals in group 2 (ESWL treated) received a thousand 18 kV shock waves after anesthetizing the rats with 50 mg/kg of ketamine. The animals in both groups were killed 72 hours after the ESWL treatment, and the parotid glands were harvested for the determination of lipid peroxidation product malondialdehyde (MDA), antioxidant glutathione (GSH) levels and the activities of antioxidant enzymes such as superoxide dismutase (SOD), GSH-Px and catalase (CAT). It was found that MDA level increased in parotid glands of rats after the ESWL treatment. The SOD, GSH-Px and CAT enzyme activities, and the level of antioxidant GSH decreased in parotid gland of rats after the ESWL treatment. It was concluded that short-term ESWL treatment caused an increase in the free radical production and a decrease in the antioxidant enzyme activity in parotid glands of ESWL-treated rats.