Holmium : YAG lithotripsy: Photothermal mechanism

Objective: A series of experiments were conducted to test the hypothesis th at the mechanism of holmium:YAG lithotripsy is photothermal, Methods and Results: To show that holmium:YAG lithotripsy requires direct a bsorption of optical energy, stone loss was compared for 150 J Ho:YAG litho tripsy of calcium oxalate monohydrate (COM) stones for hydrated stones irra diated in water (17 +/- 3 mg) and hydrated stones irradiated in air (25 +/- 9 mg) v dehydrated stones irradiated in air (40 +/- 12 mg) (P < 0.01), To show that Ho:YAG lithotripsy occurs prior to vapor bubble collapse, the dyn amics of lithotripsy in water and vapor bubble formation were documented wi th video flash photography. Holmium:YAG lithotripsy began at 60 mu sec, pri or to vapor bubble collapse. To show that Ho:YAG lithotripsy is fundamental ly related to stone temperature, cystine, and COM mass loss was compared fo r stones initially at room temperature (similar to 23 degrees C) v frozen s tones ablated within 2 minutes after removal from the freezer. Cystine and COM mass losses were greater for stones starting at room temperature than c old (P less than or equal to 0.05), To show that Ho:YAG lithotripsy involve s a thermochemical reaction, composition analysis was done before and after lithotripsy, Postlithotripsy, COM yielded calcium carbonate; cystine yield ed cysteine and free sulfur; calcium hydrogen phosphate dihydrate yielded c alcium pyrophosphate; magnesium ammonium phosphate yielded ammonium carbona te and magnesium carbonate; and uric acid yielded cyanide. To show that Ho: YAG lithotripsy does not create significant shockwaves, pressure transients were measured during lithotripsy using needle hydrophones. Peak pressures were <2 bars. Conclusion: The primary mechanism of Ho:YAG lithotripsy is photothermal, Th ere are no significant photoacoustic effects.