Influence of water temperature on pressure pulses generated by an electromagnetic type lithotripter

The need to survey and compare in vitro investigations on the effect of extracorporeally generated pressure pulses demands precise description of experimental conditions. We determined the effect of water temperature on the pressure characteristics in and around the focus area of an electromagnetic type lithotripter. The peak pressure amplitude at the geometrical focus of the lens was reduced to 60% of the original peak pressure if water at room temperature was used instead of water with human body temperature. By decreasing the temperature of the lithotripter's internal water, we observed shifting of the focus point at a rate of 1.4 mm per degree. This dramatic reduction of the peak pressure and the shifting of the focus point resulting from changes in the acoustic and thermal parameters of the propagation medium and of the focusing device could lead to differences of up to 80% of peak pressure amplitude.