The effect of single or repeated applications of "therapeutic" ultrasound on plasma extravasation during silver nitrate induced inflammation of the rat hindpaw ankle joint in vivo.

The effect of "therapeutic" ultrasound upon plasma extravasation during the inflammatory process induced in the rat hindpaw ankle by intra-articular injection of silver nitrate was investigated in two series of experiments. Both series utilised three ultrasonic frequencies, 0.75, 1.5, and 3.0 MHz, and two pulse ratios, mark:space 1:4 and 1:1. Series 1 examined the effect of two durations of ultrasound, 1 or 2 min, administered once only, and series 2 examined the effect of single or repeated insonations of 1 min duration. It was found that ultrasound treatment increased plasma extravasation compared to controls during the first 24 hr, but later reduced it significantly compared to controls. This secondary effect of reduction in plasma extravasation was delayed in animals given three insonations, this number of insonations being found to prolong the plasma extravasation phase.