Eike Matura

The mechanisms of stone disintegration by shock waves

Through interpretation of high-speed films at 10,000 frames per second of shock wave action on kidney stones and gallstones, the mechanism of stone destruction was analyzed in detail. This shows that the interaction of the shock wave with the targets firstly produces fissures in the stone material. Liquid then enters these small cracks. The actual disintegration is caused later by the enormous violence of imploding cavitation bubbles within these small split lines. That cavitation acts inside the stone and causes fragmentation even within the human gallbladder could furthermore be demonstrated by using scanning electron microscopy. These results should lead to a different process in gallstone lithotripsy leaving intervals between the shock wave treatments. This will allow the viscous bile fluids to occupy the fissures of the stones more completely and, therefore, should increase the cavitational activity on the subsequent treatment with shock pulses.

Apparatus for treating a patient with acoustic waves

An apparatus for treating a patient with acoustic waves has a source of acoustic waves and an X-ray locating system, which includes an X-ray radiator and a radiation detector, which are mounted opposite each other on a C-arm. The C-arm is adjustable along its outer circumference around its central axis. The source of acoustic waves is adjustable along the inner circumference of the C-arm such that the acoustic axis of the acoustic wave source constantly intersects the central axis of the C-arm.

In vivo assessment of shock-wave pressures: Implication for biliary lithotripsy

During extracorporeal shock-wave lithotripsy, the pressure profile, which is generated by the lithotriptor, determines the risk of tissue damage. In the present study, the pressure distribution of a lithotriptor (Lithostar; Siemens A.G., Erlangen, Federal Republic of Germany) was investigated in 10 pigs, five of which had gallstones surgically implanted into the gallbladder. The in vivo values were compared with in vitro data. Measurements were carried out along the shock-wave transmission path at the focus within the gallbladder, the adjacent liver, the diaphragmatic surface of the right lung, and the shock-wave exit site from the skin. Interposition of ribs did not cause a significant decrease in focal positive pressure. However, a gallstone positioned in the focus caused a 30%-65% reduction in pressure, recorded immediately behind the stone. Pressures obtained in vivo were always 15%-25% lower than those measured in vitro. The spatial distributions of the positive pressure in vivo and in vitro were almost identical. There was a high correlation between the pressures in vitro and in vivo (r = 0.88; P less than or equal to 0.01). This justifies assessment of shock-wave energies generated during biliary lithotripsy by extrapolation of in vitro data. It is concluded that it is possible to characterize different lithotriptors by in vitro pressure profile measurements.

Anesthetic requirements during electromagnetic extracorporeal shock wave lithotripsy.

An important aspect of modern extracorporeal shock wave lithotripsy is the ability to perform the procedure without anesthesia. Between June 1987 and April 1990, a total of 7,500 treatments were performed in our Lithotripsy Unit, using the Lithostar (Siemens AG, Erlangen, FRG): moreover 80% of the treatments were carried out as an anesthesia-free outpatient service. All treatments were reviewed for anesthetic requirements. Epidural anesthesia was performed in 74/7,500 (0.98%) treatments: during the initial period, the first 70 procedures were systematically performed under epidural anesthesia, and in 4 later cases of simultaneous endoscopic stone manipulation. Local skin infiltration was applied at the coupling site in 658/7,500 (8.7%) treatments. With increasing experience and technological improvement, 6,229/7,500 (83%) procedures were performed later on with only mild sedation: 1 mg of lorazepam orally 30 min before the treatment. Intravenous sedation was required in 510/7,500 (6.8%) cases because of painful local irritation, especially when treating calculi close to sites where shock waves can progress along the ribs. General anesthesia was required in all 28 children (0.4%).