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A Cumulative Shear Mechanism for Tissue Damage Initiation in Shock-Wave Lithotripsy

Freund, Jonathan B. and Colonius, Tim and Evan, Andrew P. (2007) A Cumulative Shear Mechanism for Tissue Damage Initiation in Shock-Wave Lithotripsy. Ultrasound in Medicine and Biology, 33 (9). pp. 1495-1503. ISSN 0301-5629. doi:10.1016/j.ultrasmedbio.2007.03.001.

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Evidence suggests that inertial cavitation plays an important role in the renal injury incurred during shock-wave lithotripsy. However, it is unclear how tissue damage is initiated, and significant injury typically occurs only after a sufficient dose of shock waves. Although it has been suggested that shock-induced shearing might initiate injury, estimates indicate that individual shocks do not produce sufficient shear to do so. In this paper, we hypothesize that the cumulative shear of the many shocks is damaging. This mechanism depends on whether there is sufficient time between shocks for tissue to relax to its unstrained state. We investigate the mechanism with a physics-based simulation model, wherein the basement membranes that define the tubules and vessels in the inner medulla are represented as elastic shells surrounded by viscous fluid. Material properties are estimated from in-vitro tests of renal basement membranes and documented mechanical properties of cells and extracellular gels. Estimates for the net shear deformation from a typical lithotripter shock (similar to 0.1 %) are found from a separate dynamic shock simulation. The results suggest that the larger interstitial volume (similar to 40%) near the papilla tip gives the tissue there a relaxation time comparable to clinical shock delivery rates (similar to 1 Hz), thus allowing shear to accumulate. Away from the papilla tip, where the interstitial volume is smaller (similar to 20%), the model tissue relaxes completely before the next shock would be delivered. Implications of the model are that slower delivery rates and broader focal zones should both decrease injury, consistent with some recent observations.

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Colonius, Tim0000-0003-0326-3909
Additional Information:© 2007 World Federation for Ultrasound in Medicine & Biology. Published by Elsevier Inc. Received 6 January 2007; revised 15 February 2007; in final form 5 March 2007. We are grateful to J. McAteer for comments on a draft of this paper. Portions of this work were supported by NIH grant PO1-DK043881.
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Subject Keywords:Shock-wave lithotripsy; Renal injury; Tissue damage; Numerical simulation
Issue or Number:9
Record Number:CaltechAUTHORS:20190718-165125075
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Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:97246
Deposited By: Melissa Ray
Deposited On:19 Jul 2019 14:45
Last Modified:16 Nov 2021 17:30

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