Laser-induced shock wave lithotripsy. Influence of laser pulse energy and irrigation solutions on stone disintegration

Experimental utilization of the holmium laser in a model of ureteroscopic lithotripsy: energy analysis

BACKGROUND AND OBJECTIVE

Medical lasers have rapidly expanded in both indications and utilization. We have developed a simple model for the investigation of various modalities of lithotripsy using readily available silicate stones of uniform mass.

MATERIALS AND METHODS

The holmium:YAG VersaPulse Select (Coherent, Palo Alto, CA) was used in these experiments to define the relation between fiber diameter and efficacy of stone fragmentation. For each fiber, lithotripsy was performed in an incremental fashion at 0.6, 0.8, and 1.0 J at a frequency of 10, 16, and 20 pulses per second at each energy level.

RESULTS

Total kilojoules did not differ between any fibers investigated, supporting the consistency of our methodology. The power density of the holmium laser energy, as expressed as total kJ/area, decreases in proportion to increasing fiber diameter. We expected an increase in fragmentation success as fiber diameter decreased (at equal energy output). However, peak lithotripsy occurred with the 365- and 550-microm fibers, whereas neither the 200- nor the 1000-microm fibers was effective.

CONCLUSION

This model utilizing a silicate stone phantom supports our clinical observation that the 365-microm fiber (and additionally the 550-microm fiber) provides the best method for efficient intracorporeal lithotripsy.

Stress-wave-induced injury to retinal pigment epithelium cells in vitro

BACKGROUND AND OBJECTIVE

To determine the survival of in vitro retinal pigment epithelium (RPE) cells subjected to laser-generated stress transients (shock waves) and compare it to that of other cell lines.

STUDY DESIGN/MATERIALS AND METHODS

Normal and transformed human retinal pigment epithelium cell lines were used. The cells were imbedded in a gel to prevent motion and cavitation and located in a thin layer at the bottom of a pipette tube closed at one end by a polyimide film. Stress transients were generated by pulsed excimer laser (193 nm and 248 nm wavelength) ablation of the polyimide film. Cell survival, compared to that of unirradiated cells, was assessed by counting surviving cells. The stress was varied from 300 to 740 bars and the number of shock wave pulses applied varied from 5 to 150.

RESULTS

Cell survival decreased sharply at the higher stresses but some cells always survived. The lowest survival rate was 50%. Increasing the number of shock wave pulses did not increase cell killing after 20 pulses, demonstrating a saturation effect. In contrast to the transformed cell line, normal cells could not be killed at the highest stress available to us.

CONCLUSION

The susceptibility of RPE cells to damage by stress waves varies with cell line. Transformed retinal pigment epithelium cells are more susceptible than normal ones. Saturation of the damage versus number of pulses is observed and a threshold-like behavior for cell killing versus stress is found. Because at least 50% of the cells survived, normal cell growth can serve to replenish damaged cells.

Comparison of 2 pulsed lasers for lithotripsy of ureteral calculi: report on 154 patients

Extracorporeal lithotripsy does not always provide satisfactory results for the treatment of ureteral stones. Such cases appear to be excellent indications for endocorporeal lithotripsy based on an association of ureteroscopy and laser. To compare the performances of 2 pulsed lasers, the pulsed dye laser (Candela) and solid Q switched laser (HMT), for the treatment of these calculi 161 ureteral stones were treated successively from November 1990 to March 1992 by a combination of ureteroscopy and laser. Endocorporeal lithotripsy was performed in 102 cases with the Candela laser, in 47 with the HMT laser and in 7 with both lasers. With a stable success rate greater than 90%, both lasers demonstrated equivalent performances regardless of the location of the stone along the ureter. However, while stone fragmentation was more rapid with the Candela laser, the HMT laser appeared to be more effective for dark stones (monohydrate calcium oxidate).