Background: Holmium laser lithotripsy research involves a number of variables that limit the wide applicability of study findings. Variables include modifiable factors such as size of the laser fiber and the type of generator used, as well as conditions not easily reproducible including the composition of stones tested and the experimental model used for the test. We describe a novel approach to standardize holmium lithotripsy experiments by using Ultracal-30 gypsum stones and by incorporating a device that hosts the stone-laser interaction and that minimizes human variability.
Materials and Methods: By altering the laser energy and pulse and consequently the power, we measured the total energy utilized by the holmium laser to break up Ultracal-30 gypsum stones. Under water, individual stones were anchored in place adjacent to the holmium laser fiber (Figure 1). The laser fiber was affixed to a specially designed sliding track for reproducible forward advancement during lithotripsy. Stone mass was evaluated before and after lithotripsy. All initial experiments were conducted on the same day using the 365 micron laser fiber. Outcomes measured include the efficacy of lithotripsy, quantified as the total energy needed for the fiber to penetrate the stone, and the residual stone mass weighed after lithotripsy.
Results: Laser settings included varied power (J) and frequency (Hz) levels. Comparison groups differed only in one of the two variables. Increasing power levels (1.0, 1.5, and 2.0 J) were compared while holding the frequency constant, as well as varying frequency levels (5 Hz vs. 10 Hz) with a constant energy of 1.0 J. After comparing the groups, we found that increasing the power from 1.0 to 1.5 J. did decrease the total energy required to penetrate the length of the stone (p<0.05), although the difference did not reach statistical significance. Small differences were also observed with other comparison groups of varying energy and frequency as well as stone weights.
Conclusion: Ultracal-30 gypsum stones incorporated into a novel experimental model device that minimizes human variability in holmium laser application may allow for the determination of optimal equipment settings, as well as comparisons of fiber instruments and operator techniques.

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