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

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 ultrasound on thrombus formation in vivo is unexplored. The present study was designed to investigate this matter.

In a blind randomized study, standardized arteriotomies and intimectomies were performed on the central arteries of the ears of 25 rabbits. The rabbits were allocated to two groups, an untreated control group and a group 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)). Immediately after reperfusion, patency was confirmed by a manual empty/refill test, after which blood-flow was monitored using ultrasonic flow-probes twice a minute for two hours. At two hours, patency was rechecked.

All vessels were patent at reperfusion, but only seven vessels (three 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 the treated group. Flow-rate curves in patent vessels in both groups were similar. Microscopic investigation at one week showed no difference in thrombus accumulation.

Ultrasound with the above characteristics does not significantly improve patency in vivo.