Introduction: Deep brain stimulation (DBS) has been used to treat movement disorders, drug resistant epilepsy, chronic pain and treatment resistant psychiatric disorders for over three decades. However, its exact mechanism of action is largely unknown or poorly understood with much debate recently about whether constant current or constant voltage imparts therapeutic effects. This study was carried out in the laboratory to compare head-to-head performances of voltage based and current based DBS-devices.
Methods: We studied two different primary cell dual channel implantable pulse generators (IPGs): the first was voltage based and the second was current based IPG. Each IPG was connected in a series circuit of standard lead-extender, standard DBS-lead, variable resistance box (representing impedance) and multimeter to measure the electric output in µAm. The IPG case was set as an anode and the DBS contact as a cathode. The output of each IPG was measured against a range of impedance from 100 to 2600O. The following IPG settings were tested: 1- amplitude (A) 2.5, pulse width (PW) 90 µS, and rate (R) 130 Hz, 2- A=3.5, PW=210 & R=130, A=5.5, PW=210 & R=130, 3- A=5.5, PW=210 & R=130, 4- A=5.5, PW=450 & R=130 and 5- A=5.5, PW=450 & R=60.
Results: Voltage based IPG output in µAm was inversely related to impedance as per Ohm’s law e.g. at setting number 2, the output was 298.4 µAm at 100O and at 2000O the output fell to 3.1 µAm. While the current based IPG output remained at constant level till 1800O where the output fell sharply to zero.
Conclusions: Constant current IPGs provided constant output at impedance of up to 1800O while constant voltage IPGs provided inverse output in relation to impedance. If the mechanism of action of DBS is dependent upon the current output then constant current IPGs should provide more reliable steady therapeutic effect with reduced requirement for reprogramming and adjustments of settings over time as the impedance varies over time.
Patient Care: By learning the difference between constant current and constant voltage patients with DBS programming might change to the better.
Learning Objectives: The delegate will learn bout the role of DBS in movement disorders and the difference between current, voltage and impedance. How these parameters affect the therapeutic effects.