3aPAa9. Damage to tissue-like structure by wrinkled focused shock waves.

Session: Wednesday Morning, May 15

Author: Danny D. Howard
Author: Bradford Sturtevant
Location: Graduate Aeronautical Labs., California Inst. of Technol., Pasadena, CA 91125


Shock waves are focused in extracorporeal shock wave lithotripsy (ESWL) machines to strengths sufficient to fracture kidney stones. Substantial side effects---most of them acute---have resulted from this procedure, including injury to soft tissue. The focusing of shock waves through various layers of tissue is a complex process which stimulates many bio-mechano-chemical responses. This paper presents preliminary results of an in vitro study of the initial mechanical stimulus. Planar nitrocellulose membranes of order 10 (mu)m thick were used as models of thin tissue structures. Scattering media were used to simulate the effects of acoustic nonuniformity of tissue and to alter the structure of focusing shock waves. Hollow glass spheres of 65 (mu)m diameter were added to ethylene glycol, glycerin, and castor oil to vary the properties of the scattering media. Multiple layer samples of various types of phantom tissue were tested in degassed castor oil to gage the validity of the scattering media. The scattering media and tissue samples wrinkled the shock structure in a similar fashion. Membranes were damaged by shear stress induced by the altered structure: after about 20 shocks immersed in the scattering media and after about 100 shocks behind the tissue samples. The mode of failure was in shear with multiple tears about 0.1 cm to about 3 cm depending on the number of shocks and membrane thickness. [Work supported by NIH Grant P01 DK43881-01A3.]

from ASA 131st Meeting, Indianapolis, May 1996