Recent developments in SWL physics research

Two projects in our laboratory highlight some recent developments in shockwave lithotripsy (SWL) physics research. In the first project, we developed a prototype of a piezoelectric annular array (PEAA) shockwave generator that can be retrofitted on a Dornier HM-3 lithotripter for active control of cavitation during SWL. The PEAA generator, operating at 15 kV, produces a peak positive pressure of approximately 8 MPa with a -6-dB beam diameter of 5 mm. The shockwave generated by the PEAA was used to control and force the collapse of cavitation bubbles induced by a laboratory electrohydraulic shockwave lithotripter with a truncated HM-3 reflector. With optimal time delay between the lithotripter pulse and the PEAA-generated shockwave, the collapse of cavitation bubbles near the stone surface could be intensified, and the resultant stone fragmentation in vitro could be significantly improved. In the second project, high-speed shadowgraph imaging was used to visualize the dynamics of lithotripter-induced bubble oscillation in a vascular phantom. Compared with the free bubble oscillation in water, the expansion of cavitation bubble(s) produced in silicone tubes and a 200-microm cellulose hollow fiber by either a Nortech EHL or a Dornier XL-1 lithotripter was found to be significantly constrained. Rupture of the cellulose hollow fiber was observed consistently after about 20 shocks from the XL-1 lithotripter at an output voltage of 20 kV. These results confirm experimentally that SWL-induced cavitation in vivo can be significantly constrained by the surrounding tissue, and large intraluminal bubble expansions could cause rupture of capillaries and small blood vessels.     

Bifocal reflector for electrohydraulic lithotripters

OBJECTIVE: To describe the design and construction of a bifocal reflector that could be used in electrohydraulic extracorporeal shockwave lithotripters in order to increase their efficiency. METHODS: The new reflector is obtained by joining two sectors of two rotationally symmetric ellipsoidal reflectors having different distances between their foci, which results in a bifocal composite reflector with the F1 foci in coincidence and the two F2 foci separated by a certain distance. As in conventional reflectors, shockwaves are generated by the electrical breakdown of water between two electrodes, located at the focus (F1) closest to the reflector. A prototype was constructed and tested in an experimental shockwave generator of our own make, using two different types of kidney-stone models, one to test the stone fragmentation abilities, and the other to test the stone pitting abilities. Fragmentation data for the new reflector were compared with those of a conventional ellipsoidal reflector tested on the same device. RESULTS: The new design appeared to be more efficient in breaking up both types of kidney-stone models than the conventional reflector. Pressure measurements were obtained with both reflectors using needle hydrophones. The physical background of shockwave reflection on both reflectors is also explained. CONCLUSION: With this new reflector, it could be possible, in principle, to reduce the treatment time of extracorporeal shockwave lithotripsy.     

Evaluation of a bifocal reflector on a clinical lithotripter

PURPOSE: To perform in vitro and in vivo tests using a clinical lithotripter in order to determine whether a bifocal reflector is more efficient and produces the same or less tissue damage than a conventional ellipsoidal reflector for electrohydraulic lithotripters. MATERIALS AND METHODS: A standard ellipsoidal and a novel bifocal reflector were tested on a Tripter Compact lithotripter (Direx Medical Systems, Petach Tikva, Israel). The bifocal reflector was constructed by joining two sectors of two rotationally symmetrical ellipsoidal reflectors having different distances between their foci. The F1 foci of the sectors coincided, creating a separation between the F2 foci. The fragmentation efficiency of the reflectors was compared using kidney-stone models. Shockwave-induced trauma was evaluated in vivo by treating both kidneys of six healthy dogs. One kidney was exposed to shockwaves generated with the conventional reflector, and the other kidney was treated using the bifocal reflector. Pressure measurements were obtained for both reflectors using needle hydrophones. RESULTS: The new design appeared to be more efficient than the conventional reflector in breaking up kidney-stone models. Tissue damage did not increase when using the bifocal reflector. CONCLUSION: The use of bifocal, instead of standard ellipsoidal, reflectors should be considered as an alternative to improve extracorporeal shockwave lithotripsy.     

CT attenuation value and shockwave fragmentation

PURPOSE: To evaluate whether, in principle, the mean CT attenuation values of kidney stones could predict fragmentation by shockwaves. MATERIALS AND METHODS: Four types of artificial kidney stones having different CT attenuation values were tested. Artificial stones were weighed and exposed to 700 shockwaves at 21 kV at the focus of an electrohydraulic lithotripter. Fragments were strained through meshes with 2x2-mm and 3.1x3.1-mm openings. The material left on the meshes after shockwave exposure was dried and weighed on a precision scale. Half of all artificial stones were saturated by immersing them in water several days before fragmentation. Fragmentation coefficients (i.e., percent weight loss) were associated with CT attenuation values using a statistical model. RESULTS: Higher CT numbers resulted in lower fragmentation coefficients. Artificial stone weight was inversely proportional to the percent weight loss. Larger fragments were obtained at lower fragmentation coefficients. Statistical analysis revealed that fragmentation can be predicted knowing the weight and the CT number of a stone before shockwave application. CONCLUSION: Prediction of the number of shockwaves necessary for successful SWL could be possible. Our statistical model proved to fit in vitro fragmentation of artificial stones; however, clinical application requires further research.     

Percutaneous stone implantation in the pig kidney: a new animal model for lithotripsy research

PURPOSE: This report describes a new animal model for research on the parameters of shockwave delivery and the mechanisms of shockwave action in SWL. MATERIALS AND METHODS: Female pigs (approximately 45 kg) were anesthetized for creation of an upper pole peripheral caliceal access. The tract was dilated with a 30F Nephromax balloon and Amplatz sheath, and a 24F rigid nephroscope was used to guide a gypsum artificial stone into a lower pole calix. An internal ureteral stent was then placed. After a 2-hour recovery period, lithotripsy was performed using an unmodified Dornier HM3 lithotripter. Following SWL, en bloc excision of the urinary tract was performed, and the stone fragments were collected. RESULTS: As observed by nephroscopy, most stones were surrounded by urine that was free of clot or debris. Urine output was >1 mL/kg per minute by the time the animal was positioned for SWL after a 2-hour observation period. When the conditions of shockwave (SW) exposure were 400 SWs, 20 kV, and 120 SW/min, the efficiency of stone fragment recovery was 85% +/- 2% (N = 6 stones). CONCLUSIONS: This procedure provides a minimally invasive method for placement of model stones of clinically relevant size within the pig kidney. Stone implantation is efficient and permits experiments to be conducted in 1 day. Stone fragmentation can be quantitated, and the animal can serve as its own control. Long-term experiments are also feasible. Overall, this new animal model is appropriate for experimentation on the parameters of SW delivery in SWL.     

Pressure-release versus rigid reflector for extracorporeal shockwave lithotripsy

PURPOSE: To evaluate the advantages and disadvantages of using a pressure-release reflector instead of a rigid reflector to concentrate shockwaves for extracorporeal shockwave lithotripsy (SWL). MATERIALS AND METHODS: As in all electrohydraulic lithotripters, shockwaves were generated by electrical breakdown of water between two electrodes, located at the focus (F1) closest to a paraellipsoidal reflector. A pressure-release reflector, made out of polyurethane foam, was constructed and tested on a research lithotripter using kidney stone models. Fragmentation data and pressure measurements were compared with those of a conventional rigid reflector tested on the same device. RESULTS: The weight of stone model fragments remaining after shockwave exposure was less with the pressure-release reflector after screening through a 3.0 x 3.0-mm mesh. The residual fragment weight was less with the rigid reflector using 1.0 x 1.0- and 0.6 x 0.6-mm meshes. CONCLUSION: Pressure-release reflectors may maintain acceptable stone fragmentation while offering improved patient safety and should be considered for SWL.     

Efficacy of the Duet lithotripter using two energy sources for stone fragmentation by shockwaves: an in vitro study

PURPOSE: To evaluate the efficacy of the Duet lithotripter's novel design of two independent spark-plug generator/reflector systems focused at a common F2. The apparatus allows either simultaneous delivery of shockwaves from both generators (resulting in a per-shock energy delivery at F2 equal to that delivered by its single generator at about 24 kV), alternating (between the two generators), or single-generator delivery of shockwaves at various energy levels and rates. MATERIALS AND METHODS: Eighty-five phantom gypsum stones (volume 786 mm3 each) were placed in a net-like basket and immersed in a specially designed waterbath coupled with the Duet lithotripter (Direx Medical Systems Ltd., Petach Tikva, Israel). Shockwaves were delivered at rates of either 60 or 120 per minute and at intensities of 16 or 22.8 kV (electrohydraulic). Energy was delivered either separately from each generator, in an alternating mode, or simultaneously from both generators. The number of shocks required to fragment the stones sufficiently to allow all of the pieces to fall through the basket holes (complete fragmentation) was recorded. RESULTS: The number of shocks required for complete fragmentation in the alternate mode (120 shocks/min, each generator rate 60/min; 22.8kV) was lower than with the single generator, 112 +/- 19 v 134 +/- 18 (at a rate of 120/min; 22.8 kV). The simultaneous mode of dual generator shockwave delivery was more effective than the traditional single generator (114 +/- 28 shocks at a rate of 120/min, 16 kV v 159 +/- 40 shocks at a rate 120/min; 22.8kV). CONCLUSION: The Duet lithotripter is more effective when used in a simultaneous or alternating mode than is the classical single mode of shock delivery, with the added benefit of shorter treatment time.     

In-Vivo relation between CT attenuation value and shockwave fragmentation

PURPOSE: To use CT attenuation numbers as a means of determining the susceptibility of an artificial stone to in-vivo fragmentation with extracorporeal shockwave lithotripsy (SWL). MATERIALS AND METHODS: Four types of artificial kidney stones having different CT attenuation values were used. One randomly selected stone was implanted in the renal pelvis of a kidney of 12 young pigs and exposed in vivo to 2500 shockwaves (21 kV) using an electrohydraulic lithotripter. Bilateral nephrectomy was performed after SWL. Fragments were strained through a mesh with a 3.1-mm grid, and the debris left on the mesh was dried and weighed. Fragmentation coefficients (FCs) were associated with CT attenuation values using a statistical model. RESULTS: The relation between FC and CT number was significant, indicating that as CT attenuation increases, FC is reduced. Larger stone fragments were obtained from stones with higher CT numbers. Initial stone weight was not a significant explanation for variations in FC. CONCLUSION: The CT values could be helpful in selecting patients for SWL in the future. However, other parameters such as stone porosity, shape, and roughness also will have to be considered.     

Synchronous twin-pulse technique to improve efficacy of SWL: preliminary results of an experimental study.

BACKGROUND AND PURPOSE: Extracorporeal shockwave lithotripsy (SWL) is the treatment of choice for the majority of renal and ureteral stones. The Dornier HM3 lithotripter has good results but with some limitations and complications. A number of second- and third-generation machines have been developed employing different energy sources, focusing devices, and coupling media. These devices overcome some of the limitations and lessen the complications but at the expense of the success rate. Use of the consecutive double-pulse technique (as in the MFL 5000) and of combined under-table and over-table modules consecutively (as in the Siemens Lithostar Plus) improves the efficacy of fragmentation. The aim of this study was to study the effects of the use of synchronous twin pulses generated by under-table and over-table identical shockwave reflectors for stone fragmentation. MATERIALS AND METHODS: We designed a lithotripter with two identical shockwave generators and identical reflectors (twin heads). One reflector was under the table and fixed, while the second reflector was over the table and hangs on a C-arm so that the angle between the axes of the two reflectors could be changed. The second focal points (F2) of the two reflectors lay in the same position. A lucent lightweight acrylic water tank with one side sealed by a silicon rubber membrane was fixed to the SWL table so that the membrane coupled with the water cushions of both reflectors. The tank was filled with degassed water and the targeted material was fixed on a holder and immersed in the water so as to be at F2. Comparison of the use of one shockwave source and two shockwave sources simultaneously was done relative to: (1) cavitation effect on aluminum foil; (2) quality of disintegration, shape of the focal zone, and ideal position of F2 using ceramic blocks; and (3) disintegrative efficacy using dental bone cement. RESULTS: The cavitation effect became more localized with the use of two reflectors. Also, the volume and rate of stone disintegration increased with the use of the two reflectors, with production of fine (<2-mm) fragments. The focal zone became smaller and conical with no propagation of shockwaves beyond F2. These results were more evident if the angle between the axes of the reflectors was 90 degrees. CONCLUSION: This new technique of SWL may improve the efficacy of treatment of urinary tract stones. It also may be less harmful to the renal tissues, but animal experiments must be carried out to prove this.     

Shockwave lithotripsy: instrumentation and status in China

PURPOSE: To introduce the physical background and technical characteristics of lithotripters made in China and to compare the efficacy of shockwave lithotripsy (SWL) for distal-ureteral stones between Chinese and Western lithotripters in consecutive use in our stone center. PATIENTS AND METHODS: From December 1987 to December 2003, we used a series of four lithotripters to treat 1802 patients with distal-ureteral stones: the piezoelectric EDAP LT-01 with ultrasound B-mode scanning for localization (N = 179); the electrohydraulic JDPN-IV lithotripter using fluoroscopy, which is made in China (N = 294), the electromagnetic Dornier Compact S with fluoroscopy/ultrasound dual localization (N = 1105), and the Huikang MZ-SWL-V, which is an electromagnetic- and electrohydraulic-compatible machine with dual localization that is made in China (N = 224). The physical background and technical characteristics of Chinese lithotripters are different from those of Western machines, but the treatment strategies were identical in all series. RESULTS: In the EDAP LT-01 series, the retreatment rate was 35.2%, and the auxiliary procedure rate was 6.7%, bring the efficiency quotient (EQ) to 69%. In the JDPN-IV series, the retreatment rate was 27.6%, the auxiliary procedure rate 1.0%, and the EQ 74%. In the Dornier Compact S series, the retreatment rate was 12.9%, and auxiliary procedures were performed in 10.9%, for an EQ of 81%. In the Huikang MZ-SWL-V series, the retreatment rate was 20.1%, the auxiliary procedure rate was 4.9%, and the EQ was 80%. CONCLUSION: The fragmentation results of Chinese electrohydraulic and electromagnetic lithotripters are superior to those of the EDAP LT-01. Chinese lithotripters are inferior to the Dornier Compact S in the efficacy of stone fragmentation, but Chinese machines cause less pain than this lithotripter.     

Operator experience and adequate anesthesia improve treatment outcome with third-generation lithotripters.

PURPOSE: To characterize the effect of operator experience and type of anesthesia on treatment outcome when switching from the Dornier HM3 to the third-generation Dornier U/50 lithotripter. PATIENTS AND METHODS: A population of 370 consecutive patients treated by 15 urologists was divided into two groups. Group I (N = 225) included patients treated during the initial 3 months with our new lithotripter. Group II (N = 145) included patients treated during the last 3 months. Changes were made during the intervening 6 months in focusing technique, anesthesia type, coupling technique, and shockwave delivery. Information was collected regarding success of stone treatment (defined as complete clearance of stone or fragments < 3 mm at 1 month). RESULTS: There were no differences between the two groups with regard to age, sex, fluoroscopic time or maximal shockwave intensity used. Group I had a slightly higher percentage of upper ureteral stones (20% v 13%); however, the difference was not significant. Upper ureteral stones in Group II were on average significantly larger (9.4 mm v 7.3 mm; P = 0.003). Intravenous sedation was used frequently in Group I (111 patients; 49%) and not at all in Group II. General anesthesia was used more frequently in Group II than in group I (34% v 24%; P < 0.02). Spinal anesthesia also was utilized more frequently in Group II patients (66% v 28%; P < 0.0001). Overall, general or regional anesthesia was received by 100% of the patients in Group II but only 52% of the patients in group I. The success rate of stone treatment was much better for Group II than for Group I (78% v 51%; P < 0.0001). CONCLUSION: The transition from a Dornier HM3 lithotripter to a third-generation lithotripter can be difficult, but if adequate anesthesia is given to minimize patient movement and balloon pressures are optimized, stone targeting can be accurate and similar stone clearance rates can be obtained.     

Extracorporeal shock wave lithotripsy using Dornier modified HM3 lithotripter comparison with the results by Dornier HM3 lithotripter

Ninety-four kidneys with renal stones less than or equal to 20 mm in diameter were treated by extracorporeal shock wave litotripsy (ESWL) using a Dornier modified HM3 lithotripter and the results were compared with those of 98 kidneys with similar size stones treated with a Dornier HM3 lithotripter. The Dornier modified HM3 lithotripter is equipped with a new type of shock wave generator with a reduced capacity for 30% less pressure peakes at the same voltage. It has an enlarged ellipsoid leading to a smaller focus and a reduced pressure per area at the shock wave entry into the skin. All treatments of modified HM3 litotripter series were performed under only intravenous analgosedation, without epidural anesthesia. The number of shock waves in the modified HM3 series ranged 900 to 6000, with the mean values of 2863 +/- 1234, which was 1.55 times as that in the Dornier HM3 series. Complete disintegration was achieved in 94 of 94 modified HM3 series kidneys and 98 of 98 kidneys of HM3 series. Complete removal of the stone was done at 72.6% in the modified HM3 series and at 70.4% in the HM3 series 3 months after ESWL. There were no severe complications in both modified HM3 series and HM3 series. Renal damage caused by ESWL was monitored by the level of urinary enzyme, N-acetyl-beta-glucosaminidase (NAG) and beta 2 microglobulin (beta 2MG) and the level of urinary protein. The levels of NAG, beta 2MG and urinary protein in the HM3 series were higher than those of the modified HM3 series.(ABSTRACT TRUNCATED AT 250 WORDS)     

Why stones break better at slow shockwave rates than at fast rates: in vitro study with a research electrohydraulic lithotripter

BACKGROUND AND PURPOSE: Stones break better when the rate of shockwave (SW) delivery is slowed. It has been hypothesized that the greater cavitation accompanying a fast rate shields pulse propagation, thus interfering with the delivery of SW energy to the stone. We tested this idea by correlating waveforms measured at the SW focus with cavitation viewed using high-speed imaging. MATERIALS AND METHODS: A series of U30 gypsum stones held in a 2-mm mesh basket were exposed to 200 SWs at 30 or 120 SW/min from a research electrohydraulic lithotripter (HM3 clone). Waveforms were collected using a fiberoptic probe hydrophone. High-speed imaging was used to observe cavitation bubbles in the water and at the stone surface. Results: Stone breakage was significantly better at 30 SW/min than at 120 SW/min. The rate had little effect on SW parameters in the water free field. In the presence of particulates released from stones, the positive pressure of the SW remained unaffected, but the trailing tensile phase of the pulse was significantly reduced at 120 SW/min. CONCLUSIONS: Cavitation bubbles do not persist between SWs. Thus, mature bubbles from one pulse do not interfere with the next pulse, even at 120 SW/min. However, cavitation nuclei carried by fine particles released from stones can persist between pulses. These nuclei have little effect on the compressive wave but seed cavitation under the influence of the tensile wave. Bubble growth draws energy from the negative-pressure phase of the SW, reducing its amplitude. This likely affects the dynamics of cavitation bubble clusters at the stone surface, reducing the effectiveness of bubble action in stone comminution.     

Dual-head lithotripsy in synchronous mode: acute effect on renal function and morphology in the pig

OBJECTIVE: To assess the effect of dual-head lithotripsy on renal function and morphology in a pig model of shockwave (SW) injury, as lithotripters with two shock heads are now available for treating patients, but little information is available with which to judge the safety of treatment with dual pulses. MATERIALS AND METHODS: A dual-head electrohydraulic lithotripter (Duet, Direx Corp., Natick, MA, USA) was used to treat the lower renal pole of anaesthetized pigs with a clinical dose of SWs (2400 dual SWs; 10 kidneys) delivered in synchronous mode, i.e. both heads fired simultaneously. For comparison, pigs were treated with either 2400 SWs (12 kidneys) or 4800 SWs (eight) with a conventional electrohydraulic lithotripter (HM3, Dornier, Wessling, Germany). RESULTS: Dual-pulse SW treatment with the Duet lithotripter caused a decline in the mean (sd) glomerular filtration rate (GFR) of 4.1 (1.9) mL/min, with a trend for the effective renal plasma flow (RPF), at 31 (19) mL/min, to also decrease. These changes in renal haemodynamics were similar to the decreases in GFR and RPF in response to treatment with the HM3 lithotripter with 2400 SWs, at 4.8 (0.8) and 32 (10) mL/min, respectively, or 4800 SWs, at 5.4 (1.0) and 68 (14) mL/min, respectively. Linear association analysis showed that the functional response to dual-pulse SWs was more variable than with conventional SWs. Morphological quantification of kidney damage (expressed as a percentage of functional renal volume, FRV) showed that tissue injury with 2400 paired SWs with the Duet, at 0.96 (0.39)% FRV, was similar to injury produced by either 2400 single SWs, at 1.08 (0.38)% FRV, or 4800 single SWs, at 2.71 (1.02)% FRV, with the HM3. However, morphological damage was less consistent with the Duet (measurable in only five of eight kidneys) than that with the HM3 (measurable in all 12 kidneys). Acoustic output and the timing of dual SWs in synchronous mode increased in variability as the electrodes aged, affecting the amplitude and targeting of focal pressures. CONCLUSION: With the caveat that variability in the timing of dual SWs will unpredictably alter the distribution of SW energy within the kidney, this study shows that a clinical dose of dual-head SWs delivered in synchronous mode elicits a renal response similar to, but more variable than, that with a clinical dose of SWs from a conventional electrohydraulic lithotripter.     

Independent assessment of a wide-focus, low-pressure electromagnetic lithotripter: absence of renal bioeffects in the pig

OBJECTIVE

To assess the renal injury response in a pig model treated with a clinical dose of shock waves (SWs) delivered at a slow rate (27 SW/min) using a novel wide focal zone (18 mm), low acoustic pressure (<20 MPa) electromagnetic lithotripter (Xi Xin‐Eisenmenger, XX‐ES; Xi Xin Medical Instruments Co. Ltd., Suzhou, PRC).

MATERIALS AND METHODS

The left kidneys of anaesthetized female pigs were treated with 1500 SWs from either an unmodified electrohydraulic lithotripter (HM3, Dornier MedTech America, Inc., Kennesaw, GA, USA; 18 kV, 30 SW/min) or the XX‐ES (9.3 kV, 27 SW/min). Measures of renal function (glomerular filtration rate, GFR, and renal plasma flow) were collected before and after SW lithotripsy, and kidneys were harvested for histological quantification of vascular haemorrhage, expressed as a percentage of the functional renal volume (FRV). A fibre‐optic probe hydrophone was used to characterize the acoustic field, and the breakage of gypsum model stones was used to compare the function of the two lithotripters.

RESULTS

Kidneys treated with the XX‐ES showed no significant change in renal haemodynamic function and no detectable tissue injury. Pigs treated with the HM3 had a modest decline from baseline (≈ 20%) in both GFR (P > 0.05) and renal plasma flow (P = 0.064) in the treated kidney, but that was not significantly different from the control group. Although most HM3‐treated pigs showed no evidence of renal tissue injury, two had focal injury measuring 0.1% FRV, localized to the renal papillae. The width of the focal zone for the XX‐ES was ≈ 18 mm and that of the HM3 ≈ 8 mm. Peak positive pressures at settings used to treat pigs and break model stones were considerably lower for the XX‐ES (17 MPa at 9.3 kV) than for the HM3 (37 MPa at 18 kV). The XX‐ES required fewer SWs to break stones to completion than did the HM3, with a mean (sd ) of 634 (42) and 831 (43) SWs, respectively (P < 0.01). However, conditions were different for these tests because of differences in physical configuration of the two machines.

CONCLUSION

The absence of renal injury with the wide focal zone XX‐ES lithotripter operated at low shock pressure and a slow SW rate suggests that this lithotripter would be safe when used at the settings recommended for patient treatment. That the injury was also minimal using the Dornier HM3 lithotripter at a slow SW rate implies that the reduced tissue injury seen with these two machines was because they were operated at a slow SW rate. As recent studies have shown stone breakage to be improved when the focal zone is wider than the stone, a wide focal zone lithotripter operated at low pressure and slow rate has the features necessary to provide better stone breakage with less tissue injury.     

Second generation shock wave lithotripsy: experience with the Siemens Lithostar

In 1980, extracorporeal shock wave lithotripsy (ESWL) was incorporated as a nonsurgical method of stone removal in the cases of nephrolithiasis and rapidly found worldwide acceptance. Several devices commonly designated "second generation" lithotripters vs "first generation" Dornier HM3 are now under experimental or clinical trial. We report our clinical experience of ESWL using a Siemens Lithostar and compared it with that obtained using a Dornier HM3. One hundred patients were treated during the period of April through October, 1986 using an HM3, and 100 other patients were treated using a Lithostar from April to August, 1988. More cases were treated with a Lithostar than with a HM3. Nearly 10% of all patients treated by ESWL required additional therapeutic approaches (excepted ureteral stent) either with HM3 or Lithostar. However, in the cases of ureteral stone, with the Lithostar more cases required adjuvant procedures (TUL) than HM3. Significantly more shock waves were needed with Lithostar than HM3 for complete fragmentation of the same size of renal and ureteral stones. The stone-free rate during a one month period after ESWL was nearly the same for HM3 and Lithostar (HM3: 84.3%, Lithostar: 83.5%). Lithostar is a multifunctional lithotriptor which has most of the advantages required by the lithotripter.     

Twenty-year prevalence of diabetes mellitus and hypertension in patients receiving shock-wave lithotripsy for urolithiasis

Study Type – Prevalence (retrospective cohort) Level of Evidence 2b What’s known on the subject? and What does the study add? Shockwave lithotripsy is a common and effective treatment method for kidney stones, but has been associated with long‐term complications, namely hypertension and diabetes. We compared the prevalence of these two disease in patients treated with lithotripsy to the background provincial population. Our analyses did not find an association between lithotripsy and the development of these diseases. Shockwave lithotripsy is an effective treatment modality for urolithiasis. The mechanism of stone communition during lithotripsy as well as the acute complications that occur following this treatment have been well described; however, the long‐term consequences of this procedure have not been clearly defined. Diabetes and hypertension have been associated with lithotripsy at 19 years follow‐up, though this relationship is controversial. This issue is further complicated by the interrelatedness of metabolic dysfunction and stone disease. Our data show that there is no association between lithotripsy and the development of either hypertension or diabetes. Patients treated for urolithiasis 20 years ago with shockwave lithotripsy were contacted, and their prevalence of diabetes and hypertension in these subjects was compared to the background population of British Columbia. The analysis also considered whether the properties of shockwaves delivered by the original Dornier HM‐3 versus a modified Dornier HM‐3 differentially affected the risk of our subjects developing these diseases. We did not find that lithotripsy, let alone the type of lithotriptor, was a risk factor for developing hypertension and diabetes. We postulate that the development of renal calculi in our subjects is more indicative of an overall metabolic syndrome where there is increasing evidence that patients with kidney stones get hypertension and diabetes and vice‐versa. The development of these diseases is not related to shockwave lithotripsy, but rather to a systemic metabolic dysfunction.

OBJECTIVES

? To compare the prevalence of hypertension and diabetes mellitus (DM) in patients treated with an unmodified HM‐3 lithotripter (USWL) and a second‐generation modified HM‐3 lithotripter (MSWL) 20 years ago at our Centre with that in the provincial population. ? To determine whether the type of lithotripter was differentially associated with the development of these sequelae.

PATIENTS AND METHODS

? Retrospective review of 727 patients at Vancouver General Hospital who underwent shock‐wave lithotripsy (SWL) between 1985 and 1989. ? Our study group was compared with Statistics Canada data describing the provincial prevalence of these diseases. ? Multivariate analysis was performed.

RESULTS

? The response rate was 37.3%. ? There was a greater proportion of overweight and obese individuals in the study group compared with the provincial average. ? In univariate analysis, lithotripsy with an unmodified HM‐3 (USWL) was associated with a higher rate of DM than the provincial rate, whereas lithotripsy with the modified HM‐3 (MSWL) was not. ? Hypertension was more prevalent in all lithotripsy subjects. ? On multivariate analysis the type of lithotripter was not associated with the development of either sequela.

CONCLUSIONS

? No association between lithotripsy and the development of either DM or hypertension in a multivariate analysis ? Metabolic syndrome may have elevated the prevalence of DM and hypertension observed in our subjects on univariate analysis, which is in keeping with the fact that our study population had statistically higher body mass indices than the provincial rate. ? Lithotripsy using the HM‐3 was not associated with increased DM or hypertension.     

Shockwave lithotripsy: anecdotes and insights

Shockwave lithotripters have evolved considerably since the introduction of the Dornier HM3 machine 20 years ago. Although shockwave lithotripsy (SWL) remains the preferred treatment for the majority of symptomatic upper urinary-tract calculi, newer lithotripters are not as effective and may have a higher risk of side effects. Lack of progress in lithotripter evolution is attributable to inadequate understanding of how and why shockwaves produce effects on stone and tissue. Current knowledge suggests that stones fragment by the mechanisms of compression fracture, spallation, squeezing, and acoustic cavitation, while tissue damage from shockwaves is secondary to cavitation and non-cavitational forces such as sheer stress. It appears likely that most tissue damage from shockwaves is caused by cavitation. As the understanding of SWL matures, new lithotripter designs may emerge that truly represent an improvement on the original Dornier HM3 machine.     

A new integrated ultrasound system for shockwave lithotripsy

BACKGROUND AND PURPOSE: Inline ultrasound monitoring requires good image quality for accurate stone localization, as well as low shockwave shadowing and a robust transducer. In general, conventional transducers designed for another purpose, such as abdominal scanning, are employed. The distance between the transducer and the SWL focus can be varied by a mechanical drive. The drawback is reduced fragmentation at short distances and poor imaging at long distances. This paper introduces a new approach using a specially designed transducer without a mechanical drive. MATERIALS AND METHODS: A transducer prototype with optimized beam focusing (B-K Medical, Herlev, Denmark) was integrated into a modified Compact Delta II therapy head (Dornier MedTech, Wessling, Germany). Image quality was tested at two clinical sites, where 40 kidney and 14 ureteral stones were treated. The shockwave was characterized by model stone tests and fiberoptic hydrophone measurements. RESULTS: Both kidney and ureteral stone treatments could be monitored reliably. Despite the long distance to the SWL focus, the transducer could be operated with relatively high frequencies (3.5-6 MHz), so that high image resolution was obtained. Model stone tests yielded the same fragmentation as the standard Compact Delta II without a transducer. CONCLUSIONS: This study shows that the concept of an integrated transducer distant from the shockwave focus is feasible. Transducer elevation, which is accompanied by shockwave shadowing and early transducer failure, is avoided by employing a dedicated transducer design.     

Effects of lithotripter-generated high energy shock waves of mammalian cells in vitro.

The effects of high energy shock waves on an established human prostatic carcinoma cell line (PC-3) were investigated. HESW were administered to PC-3 cell suspensions using an electrohydraulic lithotripter (Dornier HM3). Experimental variables included the number of shocks to which the cells were exposed, spark generator potential, and the position of the cell sample in the acoustic field. Two types of cellular damage were observed: immediate cell destruction (lysis) as measured by electronic particle counting and the loss of reproductive capacity (viability) among the remaining cells as determined by colony formation assay. Over the range of the experimental variables studied, cell lysis was dependent to a greater extent on the number of shocks administered than the generator potential. Viability was affected less but was also dependent on both the generator potential and shock number. Cell lysis was strongly dependent on the position of the sample in the acoustic field with the extent of damage increasing as the sample was moved along the central axis of the shock wave from the f2 focus towards the electrodes. Possible mechanisms of damage and the relationship of the in vitro effects to the damage observed in normal tissues of patients undergoing extracorporeal lithotripsy for kidney stone disease are discussed.