title: Stone retropulsion during holmium:YAG lithotripsy.
abstract: OBJECTIVE
  We modeled retropulsion during holmium:YAG lithotripsy on the conservation of momentum, whereby the force of ejected fragment debris off of the calculous surface should equal the force of retropulsion displacing the stone. We tested the hypothesis that retropulsion occurs as a result of ejected stone debris.
  
  
  METHODS
  Uniform calculous phantoms were irradiated with holmium:YAG energy in air and in water. Optical fiber diameter and pulse energy were varied. Motion of the phantom was monitored with high speed video imaging. Laser induced crater volume and geometry were characterized by optical coherence tomography. To determine the direction of plume laser burn paper was irradiated at various incident angles.
  
  
  RESULTS
  Retropulsion was greater for phantoms irradiated in air versus water. Retropulsion increased as fiber diameter increased and as pulse energy increased (p <0.001). Crater volumes increased as pulse energy increased (p <0.05) and generally increased as fiber diameter increased. Crater geometry was wide and shallow for larger fibers, and narrow and deeper for smaller fibers. The ejected plume propagated in the direction normal to the burn paper surface regardless of the laser incident angle.
  
  
  CONCLUSIONS
  Retropulsion increases as pulse energy and optical fiber diameter increase. Vector analysis of the ejected plume and crater geometry explains increased retropulsion using larger optical fibers. Holmium:YAG lithotripsy should be performed with small optical fibers to limit retropulsion.
authors.affiliation: Division of Urology, University of Texas Health Sciences Center, San Antonio, USA.
authors.forename: Ho
authors.initials: H
authors.lastname: Lee
authors.forename: R Tres
authors.initials: RT
authors.lastname: Ryan
authors.forename: Joel M H
authors.initials: JM
authors.lastname: Teichman
authors.forename: Jeehyun
authors.initials: J
authors.lastname: Kim
authors.forename: Bernard
authors.initials: B
authors.lastname: Choi
authors.forename: Navanit V
authors.initials: NV
authors.lastname: Arakeri
authors.forename: A J
authors.initials: AJ
authors.lastname: Welch
mesh_terms: D001696:Biomechanical Phenomena; D006801:Humans; D017602:Lithotripsy, Laser / Q000295:instrumentation; D008961:Models, Structural; D014545:Urinary Calculi / Q000628:therapy*