title: Effect of holmium:YAG laser pulse width on lithotripsy retropulsion in vitro.
abstract: OBJECTIVE
  The effect of laser pulse width on calculus retropulsion during ureteroscopic lithotripsy is poorly defined because of the limited availability of variable pulse-width lasers. We used an adjustable pulse-width Ho:YAG laser to test the effect of pulse width on in vitro phantom-stone retropulsion and fragmentation efficiency.
  
  
  METHODS
  An Odyssey 30 Ho:YAG laser (Convergent Laser Technologies, Oakland, CA) with adjustable pulse width (350 or 700 microsec) was used to treat spherical 10-mm plaster calculi in a model ureter (N = 40) and calix (N = 16) utilizing 200- and 400-microm fibers (10 Hz, 1.0 J). Calculi were placed in a waterfilled clear polymer tube, and laser energy was applied continuously in near contact until the stone had moved 8 cm. The time (seconds) and energy (joules) needed to cause the stone to traverse this distance was recorded. Stones were also placed in a stainless-steel mesh calix model in which retropulsion was limited. Laser energy was applied for 5 minutes at each pulse width. A laser-energy meter (Molectron Detector Inc, Portland OR) was used to quantify fiber transmission efficiency after 1 minute of continuous lithotripsy for each fiber at each pulse width.
  
  
  RESULTS
  Retropulsion was greater for stones treated at 350 microsec, indicated by a shorter time to traverse the model ureter. For the 200-microrm fiber at 350 microrsec, the average time was 11.5 seconds v 20.3 seconds at 700 microsec (P < 0.001). The average total energy delivered was 114.9 J at 350 microsec v 199.8 J at 700 microsec (P < 0.001). For the 400-microm fiber at 350 microsec, the average time was 5.8 seconds v 11.9 seconds at 700 microsec (P < 0.001). The average total energy was 57.1 J at 350 microsec v 127.3 J at 700 microsec (P < 0.001). In the caliceal model, at 350 and 700 microsec with the 200- and 400-microm fibers, mass loss was 34.9% and 33.4% (P = 0.8) and 14.6% and 21.6% (P = 0.04), respectively. The reduction in energy transmission at 350 microsec and 700 microsec with the 200- microm fiber after 60 seconds of continuous lasing was 8.82% v 9%, respectively (P = 0.95). For the 400-microm fiber, the transmission loss was 18.4% at 350 microsec v 4.4% at 700 microsec (P = 0.0002).
  
  
  CONCLUSIONS
  When treating ureteral calculi, retropulsion can be reduced by using a longer pulse width without compromising fragmentation efficiency. For caliceal calculi, the longer pulse width in combination with a 400-microm fiber provides more effective stone fragmentation.
authors.affiliation: Department of Urology, University of California Irvine Medical Center, Orange, California 92868, USA.
authors.forename: David S
authors.initials: DS
authors.lastname: Finley
authors.forename: Jasen
authors.initials: J
authors.lastname: Petersen
authors.forename: Corollos
authors.initials: C
authors.lastname: Abdelshehid
authors.forename: Michael
authors.initials: M
authors.lastname: Ahlering
authors.forename: David
authors.initials: D
authors.lastname: Chou
authors.forename: James
authors.initials: J
authors.lastname: Borin
authors.forename: Louis
authors.initials: L
authors.lastname: Eichel
authors.forename: Elspeth
authors.initials: E
authors.lastname: McDougall
authors.forename: Ralph V
authors.initials: RV
authors.lastname: Clayman
mesh_terms: D000535:Aluminum; D002137:Calculi / Q000601:surgery*; D006695:Holmium; D006801:Humans; D066298:In Vitro Techniques; D017602:Lithotripsy, Laser / Q000379:methods*; D008954:Models, Biological; D015019:Yttrium
chemical_list: C503779:yttrium-aluminum-garnet; D015019:Yttrium; D000535:Aluminum; D006695:Holmium