Temporal properties of transcutaneous direct current motor conduction block.

Direct current (DC) electrical block of peripheral nerve conduction shows promise for clinical applications to treat spasticity, pain, and cardiac arrhythmias. Most previous work has used invasive nerve cuffs. Here we investigate the potential of non-invasive transcutaneous direct current motor block (tDCB). In anesthetized rat, force output from the tibialis and peroneus muscles was measured in response to stimulation proximally on the sciatic nerve. DC blocking waveforms were delivered via a surface electrode placed distally on the skin over the common peroneal nerve. The efficacy of the block was observed as the reduction/abolition of muscle force. Experiments using this model were performed with two different electrode types. The amplitude and time of delivery was then adjusted to elucidate the temporal properties of block. Higher levels of DC resulted in a larger block percentage. The amount of time need to induce block depended on the level of DC with smaller amplitudes resulting in longer induction times. When block was applied for a longer period of time (120s), the block was sustained. This “recovery period” was longer for higher amplitudes of block. In addition to the temporal effects, several different clinical concerns were evaluated. Skin damage was tested using the two types of electrodes, with a higher surface area mitigating damage. In some animals the efficacy of tDCB to block tetanic muscle contractions was successfully verified. Finally, the effect of tDCB on nerve health was verified using a second distal electrode for comparison. In this study, tDCB has been shown to reversibly blocked action potentials in peripheral motor nerves. A lower amplitude applied for a longer duration can produce delayed complete block as well as delayed partial block. Also, a higher amplitude is associated with a longer recovery time. These temporal properties are important considerations for potential clinical applications.