Ureteroscopic
laser lithotripsy is a commonly used technique to treat
ureteral calculi.The type of energy source used is one of the main influences of retrograd
calculi propulsion. Using a momentum pendulum under-water set-up the induced momentum and the initial velocity were investigated.
Pulsed laser light from three different clinically available
laser systems, including a
Ho:YAG laser, a frequency-doubled double-pulse (second harmonic generation, SHG)
Nd:YAG laser and a flash-lamp pumped
dye (FLPD)
laser, were transmitted via flexible fibres of different core diameter to the front of the pendulum sinker. Single pulses at variable pulse energy, according to the clinical
laser parameter settings, were applied to the target sinker, thus causing a repulsion-induced deflection which was documented by video recording. The maximum deflection was determined. Solving the differential equation of a pendulum gives the initial velocity, the
laser-induced momentum and the efficiency of momentum transfer. The induced deflection as well as the starting velocity of the two short-duration
pulsed laser systems (SHG Nd:YAG, FLPD) were similar (s (max) = 2-3.6 cm and v (0) = 150-200 mm/s, respectively), whereas both values were lower using the
Ho:YAG laser with a long pulse duration (s (max) = 0.9--1.6 cm and v (0) = 60-105 mm/s, respectively). The momentum I induced by the
Ho:YAG laser was only 50% and its transfer efficacy η (Repuls) was reduced to less than 5% of the values of the two short-
pulsed laser systems. This investigation clearly showed the variable parts and amounts of repulsion using different
pulsed lasers in an objective and reproducible manner. The momentum transfer efficiency could be determined without any physical friction problems. Further investigations are needed to compare stone fragmentation techniques with respect to
laser repulsion and its clinical impact.