James E. Lingeman, M.D. gave a state-of-the-art lecture at the 2008 American Urological Association Meeting in Orlando, Florida titled “SWL: A Problem of Technology or Technique?”
Under a grant from the National Institute of Diabetes and Digestive and Kidney Diseases, Dr. Lingeman and colleagues at the Indiana University School of Medicine are researching ways to protect the kidney from the tissue damage that can occur with a clinical dose of shock waves. Dr. Lingeman provided up-to-date information about how shock waves break stones, the implications of that information for using lithotripsy most effectively, and how the technology might evolve in the future to leverage the new knowledge we have about how shock waves work. Dr. Lingeman is Director of Research at the Methodist Hosptial Institute for Kidney Stone Disease and co-director of the International Kidney Stone Institute, both in Indianapolis.
When the FDA approved the first lithotripsy machine in 1984, the same year Dr. Lingeman first performed the procedure, very little was known about how it worked. The machine was developed by German aircraft manufacturer Dornier.
“It was Dornier’s first medical device, and this was an entirely new field of medicine,” Dr. Lingeman said. “One of their employees, a brillaint physicist and engineer, came up with the lithotriptor concept as a variation of the systems Dornier had developed to reprodcue shock waves to test airplane parts. The physicist was the son of a German urologist, Dr. Werner Forssmann, who received the Nobel Prize in 1956 for doing the first heart catheterization on himself.”
The animal and human study data Dornier submitted to the FDA for approval of its lithotripsy machine showed no side effects from breaking the kidney stones. “When my colleagues and I did our first lithotripsy procedures in the United States, we noted that some patients were bleeding from their kidneys. Other people reported the same thing. As we began to dig into this problem, we realized that shock waves actually bruise the kidney as they go through it,” Dr. Lingeman said.
“Our research has shown that a number of factors are improtant in understanding how to make the shock waves break stones more efficiently and, at the same time, have less effect on the kidneys. One of the factors is the rate at which the shock waves are administered,” he said.
Dr. Lingeman explained that as shock waves pass through kidney stones, they compress the stones and create a negative pressure behind them. “The compressive component squeezes the stone, and the tensile component, or negative pressure, produces cavitation, which means the negative pressure creates a vacuum and forms cavities or bubbles behind the stone. The bubbles shield the stone from the next shock wave,” he said.
“We now know from our research there is an inverse relationship between the rate of shcok wave administration and the efficiency of stone fragmentation,” Dr. Lingeman continued. “The faster the shock waves are administered, the less well the stones break up. The clinical application is that if a patient’s stones are not breaking down with lithotripsy, the urologist should slow down the shock wave rate.”
Another factor important to the safety and efficiency of the lithotripotors is the size of the shock wave. “The data presented shows that the size of the shock wave relative to the stone is very important in how well the stone fragments,” Dr. Lingeman said. “if the focus of the shock wave is smaller than the size of the stone, the ability of the wave to fragment the stone is less effective than if the focus is wider than the stone.”
Dr. Lingeman also discussed how to cause less trauma to kidneys by starting the lithotriptor at a low power setting and gradually increasing the power. “The best treatment of kidney stone patients is an issue both of technology and technique.” he said.
For more information on this subject, please contact Methodist Urology at 317-962-2485.
