Parameters influencing piezoelectric shock wave lithotripsy of biliary calculi

A total of 225 human gallbladder stones were divided into sets of two, three, or four identical calculi (with maximum diameters of 6-26 mm) and submitted to piezoelectric shock wave lithotripsy in vitro in order to investigate the influence of the following parameters on stone disintegration: shock wave intensity, pulse frequency, and various physicochemical parameters such as the volume and viscosity of the fluid surrounding the stone, the hardness of the calculus, and its chemical composition. The fragmentation efficacy increased with enhanced shock wave energy (P less than 0.01). If the volume of the fluid (30 mL) surrounding the calculus was small, the disintegration end-point (defined by maximum fragment diameters less than or equal to 4 mm) was achieved after a lower number of pulses (median: 250 pulses) than in the case of a large fluid volume (80 mL) (500 pulses; P less than 0.01). On the other hand, however, factors such as the shock wave pulse rate (0.9 Hz vs 1.6 Hz), variations in viscosity of a water-jelly mixture surrounding the stone, the chemical composition of the stones as determined by X-ray diffractometry, and stone hardness were found to have no significant influence on the fragmentation efficacy.