Does ultrasound influence experimentally induced thrombus formation in thecentral artery of the rabbit ear?

Background: Thrombosis is one of the most important causes of morbidity in the medical field. Several independent in vitro studies have shown that the fibrinolytic process may be enhanced by ultrasound, but the effect of ultr asound on thrombus formation in vivo is unexplored. The present study was d esigned to investigate this matter. Methods: In a blind randomized study, standardized arteriotomies and intime ctomies were performed on the central arteries of the ears of 25 rabbits. T he rabbits were allocated to two groups, an untreated control group and a g roup treated with ultrasound (10 pulses of frequency 1 MHz and intensity 1 W/cm(2) per millisecond giving an averaged intensity of 0.01 W/cm(2)). Imme diately after reperfusion, patency was confirmed by a manual empty/refill t est, after which blood-flow was monitored using ultrasonic flow-probes twic e a minute for two hours. At two hours, patency was rechecked. Results: All vessels were patent at reperfusion, but only seven vessels (th ree control, four treated) were patent when flow-rate measurements started. At 2 h, patency-frequencies were 12/23 in the control group and 11/22 in t he treated group. Flow-rate curves in patent vessels in both groups were si milar. Microscopic investigation at one week showed no difference in thromb us accumulation. Conclusions: Ultrasound with the above characteristics does not significant ly improve patency in vivo.