Purpose: To study the effect of altering shockwave frequency on the efficiency of stone fragmentation using the MFL 5000 spark-gap lithotripter.
Materials and methods: Standardized solid plaster stones, 12.0 +/- 0.5 mm in diameter, were fragmented at an energy setting of 20 kV. The shockwave frequencies tested were 60, 80, and 117 per minute. Stones were fragmented throughout the entire lifespan of the electrode, from 0 to >100% consumption, at each frequency tested. Electrode pressure output was studied for each frequency.
Results: A greater number of shocks was required to fragment the plaster balls at higher frequencies (regression coefficient 1.93; p < 0.003). An inverse relation was found between the number of shocks necessary to break the stones and electrode consumption (regression coefficient -2.16; p < 0.001). The analysis of delivered pressure from the electrode failed to demonstrate a linear relation with frequency (regression coefficient -0.40; p < 0.728) or consumption (regression coefficient -1.11; p < 0.158).
Conclusions: The number of shocks required to fragment a stone is influenced in part by the frequency at which the shockwaves are delivered. Increasing the shockwave frequency from 60 to 117 per minute in this study caused a significant rise in the number of shocks required to break the stone. The pressure output of the electrode was similar at the frequencies tested, thus making the difference in stone fragmentation secondary to the mechanism of stone disintegration and not the function of the electrode.