Effects of high-intensity focused ultrasound on nerve conduction

The effects of various exposures (intensity, duration) of high-intensity focused ultrasound (HIFU) on sciatic nerve conduction were investigated in vivo in rats. The objective was to identify HIFU exposures that produce biological effects ranging from partial to complete conduction block, indicating potential use of HIFU as an alternative to current clinical methods of inducing nerve conduction block. In the study, 26 nerves were exposed and treated with 5-s applications of 5.7-MHZ HIFU with acoustic intensities of 390, 2,255, 3,310, and 7,890 W/cm(2) (spatial peak, temporal peak). Compound muscle action potentials (CMAPs), in response to electrical stimulation of the nerve proximal to the HIFU site, were recorded from the plantar foot muscles immediately before and after HIFU treatment and 2 and 4 h after treatment. Furthermore, a preliminary long-term investigation was performed on 27 nerves with the same four sets of HIFU parameters. CMAPs were measured at the survival endpoint for each animal (7 or 28 days after treatment). For nerves treated with the three lower exposures, CMAPs decreased initially within 4 h or 7 days after HIFU treatment and then recovered to their baseline level at 28 days after treatment. For the highest exposure, however, CMAPs remained absent even 28 days after treatment. These exposure-dependent effects of HIFU on nerve function suggest its future potential as a novel treatment for severe spasticity and pain.