There is some slight attenuation of transmission through tissue. The pressure that's generated is about 14,000 pounds per square inch, but you do lose energy when there's a different acoustical interface, and the place where that really occurs in the body is air. In our patients, I tell them to take some Mylicon to try to decrease the amount of bowel air as possible. We're going through the retroperitoneum so there's rarely air between where I'm generating the shock wave and where the shock wave is going to be developed. Again, you'll be close to the abdominal wall, there's not going to be much air between the abdominal wall and the gallbladder, so I don't think it's going to be much trouble. I'll tell you where it can become a problem, though, is in children. I doubt there's many children with gallstones that you'll be treating, but we treat a number of children with stones, and their lungs when they take a deep breath, the diaphragm is just above the kidney and you can actually shock wave the lung and when there's that acoustical interface we have seen some hemoptysis ¾ haven't had anybody get in any trouble with it, but they can create some damage there.
We've also had the opportunity to operate one time, very early in our experience, and of note was that there were petechiae around the bowel when we did do that surgery and I'm sure that's because there was an air-water interface at that point. There was no problem with the patient, just notice that there were these small petechiae along the bowel.