Local Analgesia from Percutaneous Electrical Stimulation: A Peripheral Mechanism

Pain and touch thresholds to a needle stimulus were measured on a finger of each of 11 subjects as a function of the presence or absence of continuous, 100-hertz, 1-msec electrical stimulation delivered proximally to the digital nerves of the finger tested at intensities of either 10 to 12 v, 22 v, or 50 v. At 10 to 12 v touch threshold alone was elevated; at 22 v both touch and pain thresholds were elevated; and at 50 v anesthesia and analgesia resulted. The averaged median nerve compound action potential resulting from either periodic bursts or continuous 50-v, 100-Hz, 0.5-msec duration electrical stimulation to the digital nerves of a finger was studied in each of five subjects. An A-delta wave was recorded with periodic bursts of stimuli, but was absent with continuous stimulation. These results indicate that analgesia from electrical stimulation results from peripheral blockade of A-delta fibers.