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F H Cocks

Publications and source records attributed to F H Cocks.

18 recordsLinked to original sources
PubMed1997

Controlled, forced collapse of cavitation bubbles for improved stone fragmentation during shock wave lithotripsy.

The feasibility of using controlled, forced collapse of cavitation bubbles for improved stone fragmentation during shock wave lithotripsy was demonstrated using microsecond tandem shockwave pulses. High-speed photography revealed that a secondary shock wave, released in less than 500 microseconds (microsec.) following a lithotripter-generated shock wave, can be used to control and force the collapse of cavitation bubbles toward target concretions. This timely enforced shockwave-bubble interaction was found to greatly enhance the cavitational activity near the stone surface, with a resultant up to 43% increment in stone fragmentation. Since most of the cavitation energy is directed and concentrated toward the target stones and fewer shock waves are needed for successful stone comminution, tissue injury associated with this new lithotripsy procedure may also be reduced. This novel concept of shock wave lithotripsy may be used to improve the treatment efficiency and safety of existing clinical lithotripters, as well as in the design of new shock wave lithotripters.

Feasibility Studies↗
PubMed1997

Transient oscillation of cavitation bubbles near stone surface during electrohydraulic lithotripsy.

Using high-speed photography and acoustic emission measurements, we studied the dynamics of a transient cavitation bubble near a stone surface and the concomitant shockwaves generated during electrohydraulic lithotripsy (EHL). At each spark discharge, a vapor plasma and subsequently a cavitation bubble oscillating around the tip of an EHL probe are produced. Simultaneously, three distinctive shockwave pulses are generated. The first shockwave is produced by the rapid expansion of the vapor plasma, while the second and third waves are produced by rebounds of the cavitation bubble. Depending on the proximity of the probe to the stone surface, the collapse of the cavitation bubble may be symmetric, resulting in a strong shockwave emission; or asymmetric, leading to the formation of a liquid jet. For the Nortech AUTOLITH lithotripter with a 1.9F probe that was used in this study, maximum shockwave emission is produced when the probe is about 1 mm from the stone surface, whereas the maximum jet velocity is produced when the probe tip is at distance equivalent to the maximum bubble radius of about 3 mm. These findings are consistent with clinical experience, which suggests that for optimal treatment results, the EHL probe should be placed close to the stone surface.

Acoustics↗
PubMed1997

Inertial cavitation and associated acoustic emission produced during electrohydraulic shock wave lithotripsy.

The inertial cavitation and associated acoustic emission generated during electrohydraulic shock wave lithotripsy were studied using high-speed photography and acoustic pressure measurements. The dynamics of cavitation bubble clusters, induced in vitro by an experimental laboratory lithotripter, were recorded using a high-speed rotating drum camera at 20,000 frames/s. The acoustic emission, generated by the rapid initial expansion and subsequent violent collapse of the cavitation bubbles, was measured simultaneously using a 1-MHz focused hydrophone, The expansion duration of the cavitation bubble cluster was found to correlate closely with the time delay between the first two groups of pressure spikes in the acoustic emission signal. This correlation provides an essential physical basis to assess the inertial cavitation produced by a clinical Dornier HM-3 shock wave lithotripter, both in water and in renal parenchyma of a swine model. In the clinical output voltage range (16-24 kV), the expansion duration of the primary cavitation bubble cluster generated by the HM-3 lithotripter in water increases from 158 to 254 microseconds, whereas the corresponding values in renal parenchyma are much smaller and remain almost unchanged (from 71 to 72 microseconds). In contrast, subsequent oscillation of the bubble following its primary collapse is significantly prolonged (from 158-235 microseconds in water to 1364-1373 microseconds in renal parenchyma). These distinctive differences between lithotripsy-induced inertial cavitation in vitro and that in vivo are presumably due to the constraining effect of renal tissue on bubble expansion.

Acoustics↗
PubMed1995

A novel variable-gravity simulation method: potential for astronaut training.

Zero gravity conditions for astronaut training have traditionally used neutral buoyancy tanks, and with such tanks hypogravity conditions are produced by the use of supplemental weights. This technique does not allow for the influence of water viscosity on any reduced gravity exercise regime. With a water-foam fluid produced by using a microbubble air flow together with surface active agents to prevent bubble agglomeration, it has been found possible to simulate a range of gravity conditions without the need for supplemental weights and additionally with a substantial reduction in the resulting fluid viscosity. This new technique appears to have application in improving the simulation environment for astronaut training under the reduced gravity conditions to be found on the moon or on Mars, and may have terrestrial applications in patient rehabilitation and exercise as well.

Astronauts↗
PubMed1993

Would revision arthroplasty be facilitated by extracorporeal shock wave lithotripsy? An evaluation including whole bone strength in dogs.

Extracorporeal shock-wave lithotripsy has been proposed as a modality to facilitate the removal of bone cement during revision arthroplasty; however, concomitant cortical microfractures have been reported. The current study examines the effect on whole bone strength of extracorporeal shock-wave lithotripsy directed at the cement-bone complex. Canine femora were subjected to manual cement extraction or lithotripsy followed by manual cement extraction. Contralateral femora served as controls. Torsional fractures were created, and maximum torque, maximum angular displacement, and energy capacity to failure were determined. Although cement extraction alone reduced mean torque by 6.6% and failed to reduce mean torque angle or mean energy capacity, the combination of lithotripsy and cement extraction reduced mean torque by 7.3%, mean torque angle by 14.3%, and mean energy capacity by 18.3%. No statistical significance was demonstrated between the two groups in torque, angle, or energy capacity. At magnitudes and numbers of shock waves previously shown to significantly reduce cement-bone interface mechanical strength, lithotripsy exposure had a minimal and insignificant effect on whole bone strength.

Animals↗
PubMed1990

Mechanical property studies of human gallstones.

The recent development of gallstone fragmentation methods has increased the significance of the study of the mechanical properties of human gallstones. In the present work, fracture strength data and microhardness values of gallstones of various chemical compositions are presented as tested in both dry and simulated bile environments. Generally, both gallstone hardness and fracture strength values were significantly less than kidney stone values found in previous studies. However, a single calcium carbonate stone was found to have an outer shell hardness exceeding those values found for kidney stones. Diametral compression measurements in simulated bile conclusively demonstrated low gallstone fracture strength as well as brittle fracture in the stones tested. Based on the results of this study, one may conclude that the wide range of gallstone microhardnesses found may explain the reported difficulties previous investigators have experienced using various fragmentation techniques on specific gallstones. Moreover, gallstone mechanical properties may be relatively sensitive to bile-environment composition.

Bile↗
PubMed1987

Extracorporeal shock wave lithotripsy: the use of chemical treatments for improved stone comminution.

Extracorporeal shock wave lithotripsy (ESWL) can require more than two thousand acoustic shocks to achieve an adequate degree of renal calculus comminution. A decrease in the number of shocks necessary for effective treatment offers both technical and clinical benefits. The results presented here demonstrate that it is possible in particular cases to increase substantially the degree of comminution produced using a fixed number of acoustic impulses by exposing the stones to solutions of controlled pH and chemical composition during acoustic shock treatment. The largest increase in comminution was observed for magnesium ammonium phosphate hexahydrate/apatite stones exposed to citrate solutions. The smaller particle sizes are shown to result not only from stone dissolution but also from an increase in the ease of stone fracture during acoustic shocking. The degree of comminution of the largest fragment sizes was also found to be slightly increased for calcium oxalate stones by exposure to synthetic urine of elevated pH. These chemical methods of increased stone comminution appear to be directly applicable to particular cases and may have general clinical utility if suitable conditions affecting all stones can be found.

Calcium Oxalate↗
PubMed1986

Effect of pH on the microhardness of renal calculi.

The effects of synthetic urine environments of pH 4, 6, and 9.5 on the microhardness of renal calculi have been investigated. Tests were made, using both Vickers and Knoop indenters, on three compositions of calculi: 100% calcium oxalate monohydrate (whewellite), 100% uric acid, and 98% magnesium ammonium phosphate hexahydrate (struvite) mixed with 2% carbonate apatite. Whewellite calculi hardness was lowered, relative to (dry) values by 45-55% when saturated with a solution of pH 9.5. Exposure to lower pH conditions was not as effective in lowering hardness in this case. Struvite calculi hardness was lowered by 41-52% compared to the dry hardness and uric acid calculi hardness decreased by 25-36%, compared to dry hardnesses. For uric acid stones the reduction in hardness did not depend on pH within the range of pH values investigated. For struvite stones, acid pH conditions appear to give an increased softening, compared to other pH values.

Biomechanical Phenomena↗
PubMed1980

Measurement of in vivo corrosion rates in baboons, and correlation with in vitro tests.

The Lineal Polarization Technique was used to determine the polarization resistances and corrosion currents of various dental restorative and implant alloys and amalgams placed in the teeth of animals, and as laboratory samples in artificial saliva. Gold- and chromium-containing alloys corroded the least, and amalgams generated the highest corrosion currents. There was good agreement between measurements made in vivo and in vitro. This is the first time that corrosion current have been measured in the mouth repeatedly over a long time span. These methods may be developed into useful predictive tests of in vivo corrosion.

Animals↗
PubMed1980

Corrosion behavior of Au and Ag modified Cu-Ni-Mn alloys.

The linear electrochemical polarization method was used to provide quantitative in vitro measurements of corrosion rates as a function of exposure time for Cu-Ni-Mn, Cu-Ni-Mn-Au, Cu-Ni-Mn-Ag, and Cu-Ni-Mn-Au-Ag alloys in artificial saliva. Both Au and Ag additives to dental-cast Cu-Ni-Mn alloys lowered the corrosion rate significantly.

Copper↗
PubMedDate not supplied

Experimental laboratory lithotripter: design, construction, and operation.

A laboratory lithotripter has been constructed and used to comminute (crush to a powder) both kidney stones and gallstones. The stones are placed in the second focus (f2) of an ellipse of revolution whose linear eccentricity is 4.7 cm and then acoustically shocked an average of 200 times by an underwater spark discharge at the first focus (f1). The energy levels available from the capacitors (3 to 52 joules) of this unit extend below and above the range of commercially available clinical devices. The electrical and mechanical design of this unit is presented. At a relatively low cost (approximately $15,000) the unit appears to have considerable application in non-clinical research in lithotripsy. Quantitative results of the application of this device to the comminution of human kidney stones are presented.

Cholelithiasis↗