A constant current peripheral nerve stimulator (Neurostim T4). Description, and evaluation in volunteers

A pocket-size, battery-powered peripheral nerve stimulator featuring a calibrated constant current floating output (max. 80 mA) was evaluated in unanaesthetized volunteers. Modes of stimulation included continuous 1 Hz, continuous train-of-four every 15 s, and on-demand tetanus (50 Hz per 5 s). Within the limits of 0-250 V, voltage adjusted automatically for 0.2-ms monophasic square pulses. Between 20 and 80 mA, the dial error of current intensity was less than +/- 5%. Maximum allowable resistance for the generation of 40-mA pulses was 5 k omega--that is five times the average tissue impedance as measured in 15 volunteers. With surface electrodes, the current intensity required for maximal indirect muscle stimulation in another 50 individuals was 38 +/- 23 mA (mean +/- SD). With up to 80 mA stimulus current, supramaximal nerve stimulation was obtained in 94% of the volunteers.