Spasticity and pain are significant complications of neurological disorders and injuries. Common treatments include nerve conduction blocks, via chemical blocks and surgical interventions, which can be invasive and do not benefit all patients. High-intensity focused ultrasound (HIFU) is a therapeutic modality that can non-invasively achieve focal heating and mechanical disruption of small volumes of internal tissue without damaging intervening tissues. By employing these unique capabilities of HIFU, the goal of this research has been to investigate the use of HIFU as a novel method of nerve conduction block. The range of effects, from partial to complete block, which can be achieved with variance in HIFU dose, has also been investigated. HIFU-induced nerve blocks could potentially provide more effective treatment of spasticity and pain.; Initial work determined the feasibility of ultrasound image-guided HIFU to target and block the sciatic nerves of rabbits. HIFU with frequency of 3.2-MHz, 1480-1930W/cm2 intensity and duration of 5--40sec produced complete conduction block in 34 rabbit sciatic nerves. Ultrasound imaging was used for HIFU targeting and monitoring. In long-term investigations such blocks resulted in distal axon degeneration.; Furthermore, preliminary investigations suggested a range of dose-dependent effects of HIFU on rat sciatic nerve conduction over 28 days. Four doses of 5.7-MHz HIFU (390--7890W/cm2, 5sec duration) were applied directly to 53 exposed rat sciatic nerves and the amplitude of compound muscle action potentials (CMAP) in the foot were observed over time (groups observed at 0, 7, or 28 days). For groups treated with the three lower doses, CMAP decreased up to 4 hours or 7 days after HIFU treatment yet recovered to near baseline by 28 days. CMAP remained negligible at 28 days for the group treated with the highest dose. For each time point group, CMAP amplitude diminished with increased HIFU dose.; These in vivo investigations indicate that HIFU can produce dose-dependent effects on nerve conduction ranging from partial and temporary block to complete and permanent block. A graded suppression of nerve conduction could enhance the clinical potential of HIFU: applications include treatment of spasticity in patients with spinal cord injury or pain in cancer patients.
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