Biomedical subjects

James C Williams

Publications and source records attributed to James C Williams.

24 records · Page 2Linked to original sources

PubMed2003

In vitro assessment of ultrasonic lithotriptors.

PURPOSE: Ultrasonic lithotriptors are commonly used to fragment and remove stones during percutaneous nephrolithotomy. To date a comparative assessment of current units has not been accomplished without potential operator bias. An objective testing environment is required for optimal appraisal of the efficiency of ultrasonic lithotriptors. MATERIALS AND METHODS: An in vitro test system was devised to evaluate the ability of ultrasonic lithotriptors to core through artificial stones. The system consisted of an irrigation sheath (Cook Urological, Spencer, Indiana) through which ultrasonic probes were placed. Ultrasonic hand pieces and probes were secured in an upright position. An Ultracal-30 (U.S. Gypsum, Chicago, Illinois) stone cylinder (mean length 12.8 +/- 0.6 mm, mean diameter 7.6 +/- 0.07 mm) was centered on the probe tip. A weight (62.7 gm) was placed atop the stone to provide a constant force. We evaluated the Olympus LUS-1 and LUS-2 (Olympus, Melville, New York), Circon-ACMI USL-2000 (Circon-ACMI, Southborough, Massachusetts), Karl Storz Calcuson (Karl Storz, Culver City, California) and Richard Wolf model 2271.004 (Richard Wolf, Vernon Hills, Illinois). All probes had outer diameters of 3.4 mm except for the Circon-ACMI unit (3.8 mm). Using 100% power settings times for complete stone penetration were assessed for all units. Differences in mean stone penetration times were compared using ANOVA. RESULTS: The Olympus LUS-2 had the fastest mean stone penetration time (28.8 +/- 2.7 seconds). This value was used to normalize the data into efficiency ratios, where other unit times were expressed as multiples of the LUS-2 time: Olympus LUS-2 (1.0 +/- 0.1) equals Circon-ACMI USL-2000 (1.1 +/- 0.3) greater than Karl Storz Calcuson (1.4 +/- 0.3) greater than Olympus LUS-1 (2.1 +/- 0.5) greater than Richard Wolf (3.6 +/- 0.8). Efficiencies of the LUS-2 and USL-2000 units were essentially equivalent, with all others significantly less efficient (p <0.05). CONCLUSIONS: This new in vitro testing model provides an objective, reproducible method for evaluating the efficiency of intracorporeal lithotriptors. Of the units tested the Olympus LUS-2 and Circon-ACMI USL-2000 were the most efficient.

Equipment Design↗

PubMed2002

Stone fragmentation during shock wave lithotripsy is improved by slowing the shock wave rate: studies with a new animal model.

PURPOSE: The current trend toward ungated shock wave lithotripsy means that more patients are being treated with shock waves delivered at a rapid rate (120 shock waves per minute or greater). However, no benefit of an increased shock wave rate has been shown and in vitro studies indicate that slowing the shock wave rate actually improves stone fragmentation. We tested the effect of the shock wave rate on stone comminution in a new animal model. MATERIALS AND METHODS: Gypsum model stones were inserted via upper pole percutaneous access into the lower pole calix of the kidneys of female pigs weighing approximately 100 pounds. Shock wave lithotripsy was performed (400 shock waves uninterrupted at 20 kV. and 30 or 120 shock waves per minute) 2 hours later using an unmodified HM3 lithotriptor (Dornier Medical Systems, Marietta, Georgia). After en bloc excision of the urinary tract stone fragments were collected and sieved through 2 mm. mesh. The particles were weighed and surface area was determined. RESULTS: Stones treated at 30 shock waves per minute broke more completely than stones treated at 120 shock waves per minute. The percent of fragments greater than 2 mm. was significantly higher for stones treated at the fast rate of 120 versus the slow rate of 30 shock waves per minute (mean +/- SEM 81% +/- 14% versus 45% +/- 12%, p <0.005). When stone fragmentation was expressed as the percent increase in fragment surface area, significantly greater fragmentation occurred at the slower than at the more rapid rate (327% +/- 63% versus 135% +/- 136%, p <0.02). CONCLUSIONS: Slowing the rate of shock wave administration during shock wave lithotripsy significantly improves the efficiency of stone fragmentation in vivo.

Animals↗

PubMed2002

Kidney damage and renal functional changes are minimized by waveform control that suppresses cavitation in shock wave lithotripsy.

PURPOSE: In studies to understand better the role of cavitation in kidney trauma associated with shock wave lithotripsy we assessed structural and functional markers of kidney injury when animals were exposed to modified shock waves (pressure release reflector shock pulses) that suppress cavitation. Experiments were also performed in isolated red blood cells, an in vitro test system that is a sensitive indicator of cavitation mediated shock wave damage. MATERIALS AND METHODS: We treated 6-week-old anesthetized pigs with shock wave lithotripsy using an unmodified HM3 lithotriptor (Dornier Medical Systems, Marietta, Georgia) fitted with its standard brass ellipsoidal reflector (rigid reflector) or with a pressure release reflector insert. The pressure release reflector transposes the compressive and tensile phases of the lithotriptor shock pulse without otherwise altering the positive pressure or negative pressure components of the shock wave. Thus, with the pressure release reflector the amplitude of the incident shock wave is not changed but cavitation in the acoustic field is stifled. The lower pole of the right kidney was treated with 2,000 shocks at 24 kV. Glomerular filtration rate, renal plasma flow and tubular extraction of para-aminohippurate were measured in the 2 kidneys 1 hour before and 1 and 4 hours after shock wave lithotripsy, followed by the removal of each kidney for morphological analysis. In vitro studies assessed shock wave induced lysis to red blood cells in response to rigid or pressure release reflector shock pulses. RESULTS: Sham shock wave lithotripsy had no significant effect on kidney morphology, renal hemodynamics or para-aminohippurate extraction. Shock waves administered with the standard rigid reflector induced a characteristic morphological lesion and functional changes that included bilateral reduction in renal plasma flow, and unilateral reduction in the glomerular filtration rate and para-aminohippurate extraction. When the pressure release reflector was used, the morphological lesion was limited to hemorrhage of vasa recta vessels near the tips of renal papillae and the only change in kidney function was a decrease in the glomerular filtration rate at the 1 and 4-hour periods in shock wave treated kidneys. Red blood cell lysis in vitro was significantly lower with the pressure release reflector than with the rigid reflector. CONCLUSIONS: These data demonstrate that shock wave lithotripsy damage to the kidney is reduced when cavitation is suppressed. This finding supports the idea that cavitation has a prominent role in shock wave lithotripsy trauma.

Animals↗

PubMed2002

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.

Animals↗

PubMed2002

Effect of overpressure and pulse repetition frequency on cavitation in shock wave lithotripsy.

Cavitation appears to contribute to tissue injury in lithotripsy. Reports have shown that increasing pulse repetition frequency [(PRF) 0.5-100 Hz] increases tissue damage and increasing static pressure (1-3 bar) reduces cell damage without decreasing stone comminution. Our hypothesis is that overpressure or slow PRF causes unstabilized bubbles produced by one shock pulse to dissolve before they nucleate cavitation by subsequent shock pulses. The effects of PRF and overpressure on bubble dynamics and lifetimes were studied experimentally with passive cavitation detection, high-speed photography, and B-mode ultrasound and theoretically. Overpressure significantly reduced calculated (100-2 s) and measured (55-0.5 s) bubble lifetimes. At 1.5 bar static pressure, a dense bubble cluster was measured with clinically high PRF (2-3 Hz) and a sparse cluster with clinically low PRF (0.5-1 Hz), indicating bubble lifetimes of 0.5-1 s, consistent with calculations. In contrast to cavitation in water, high-speed photography showed that overpressure did not suppress cavitation of bubbles stabilized on a cracked surface. These results suggest that a judicious use of overpressure and PRF in lithotripsy could reduce cavitation damage of tissue while maintaining cavitation comminution of stones.

Equipment Design↗

PubMed2002

High resolution detection of internal structure of renal calculi by helical computerized tomography.

PURPOSE: There is considerable interest in using radiological imaging to predict kidney stone fragility before patient treatment. Case series of shock wave lithotripsy show that shock wave lithotripsy is repeated and/or ancillary procedures are done to remove shock wave resistant stones in a significant number of cases. If the fragility of stones were predicted at diagnosis, unnecessary shock wave treatment would be avoided. However, plain radiography allows little discrimination of stone type and simple numerical analysis of computerized tomography (CT) images by measuring Hounsfield units has been shown to be limited in its ability to predict stone fragility. MATERIALS AND METHODS: Urinary stones of known composition were imaged by helical CT in vitro at various slice widths and the images were assessed using a range of window settings. RESULTS: Visualization of stone structure was greatly enhanced using bone windows and a narrow slice width. Surface structure, such as crystalline leaves of calcium oxalate dihydrate, and internal structure showing the heterogeneity of composition or cracks were detected. Stones of similar mineral composition differed dramatically in terms of CT visible structure. CONCLUSIONS: Using a narrow slice width and bone windows greatly improves the visualization of kidney stone structure on helical CT. These results open up new possibilities for determining the relationship of stone structure and fragility for shock wave lithotripsy.

Humans↗