Biological effects of shock waves: cavitation by shock waves in piglet liver.

Shock waves are known to generate cavitation in vitro. In vivo, extracorporeal shock waves may cause haemorrhages in tissues. Two types of changes were detected by conventional, real-time B-scan ultrasound when shock waves were administered to 5 piglet livers in vivo: transient changes consisting of bright signals in intrahepatic branches of the portal vein and tributaries of the hepatic vein, presumed to originate from gas bubbles, and stationary changes consisting of brightening of the area along the long axis of the high pressure field, presumed to indicate an increased number of gas-filled bubbles in this area. Transient changes appeared from the start of shock wave administration; bright signals were seen in liver vessels for several hundred microseconds before they were flushed away with the blood flow. Stationary changes appeared later, increased in intensity over several hundred shock waves and persisted for minutes after cessation of shock wave administration. Both types of signals were interpreted as direct evidence that lithotripter shock waves generated cavitation in vivo. Similar signals were received in the partly degassed water of the lithotripter tub. At autopsy of the piglets, focal intralobular haemorrhages and thrombi of portal veins were detected in the shock wave path. The occurrence of cavitation and tissue damage in the same gross area suggests that cavitation might be involved in the generation of tissue damage by shock waves.