Effect of Pulse Width on Object MovementIn VitroUsing Holmium:YAG Laser

Abstract

Background and Purpose: The holmium:YAG laser is an effective modality for intracorporeal lithotripsy. The fiber tip needs to be in contact with the calculus for maximal effect. Laser energy can cause stone retropulsion, necessitating cumbersome repositioning of the fiber. We examined the effect of varying the laser pulse width on object movement in vitro. Materials and Methods: Two experiments were conducted using a holmium:YAG laser at the 350-μsec and 700-μsec pulse-width settings. In the first experiment, one pulse was delivered to a non-fragmentable ball bearing at increasing energy settings, and object displacement was measured. In the second experiment, a train of pulses was delivered to a fragmentable soda lime phantom at increasing energy settings, and the total energy delivered before movement from the tip of the fiber was determined. Results: The mean ball bearing movement was significantly greater at the 350-μsec setting with a 200-μm fiber (P < 0.0001), as well as a 400-μm fiber (P < 0.0069). More disparity in movement was noted at higher energy settings. The total energy delivered to the soda lime phantom before migration was significantly greater using the 700-μsec setting (P < 0.0018). Conclusions: Pressure waves from Ho:YAG lithotripsy are less than with other modalities, yet some retropulsion occurs. The duration of the laser pulse can influence shockwave generation and object migration. Longer pulse width results in less object movement after one shock and more energy delivery during repetitive shocks. Clinically, this regimen may reduce the need for fiber readjustment and lead to more efficient stone fragmentation.