Conference ProceedingsThe Rationale Driving the Evolution of Deep Brain Stimulation to Constant-Current Devices
Section snippets
INTRODUCTION
Deep brain stimulation (DBS) is an effective therapy for the treatment of select patients with advanced Parkinson’s disease, dystonia, tremor, and neuropsychiatric disorders. Long-term follow-up data for 10 years and beyond have begun to emerge, and challenges as well as opportunities for improving the technology have been presented. The effectiveness and, conversely, the side effects of DBS depend on what gray and white matter brain structures are affected and on the density of stimulation in
WHY IMPEDANCE MATTERS IN DBS
Impedance plays a critical role in how stimulation is delivered to the brain. Under voltage-based stimulation, electrode impedance directly predicts the amount of current delivered to the tissue (Figs. 1 and 2). The current delivery dictates the volume of tissue activated (VTA) through the use of specific stimulation parameters. Constant-current stimulation has the advantage of reducing the number of variables needed to maintain a constant VTA. Under constant-current or voltage stimulation,
MEASURING IMPEDANCE
When a user requests an impedance measurement from the programmer, for each contact a short test pulse of known current (I) is delivered to the contact using the case as a return electrode, and the voltage required to deliver the current (V) is measured. The access resistance is computed as V/I for each contact and reported to the user.
Accurately measuring impedance is clearly important if it changes over time. The impedance-checking capabilities of the different devices were assessed by Patel
DOES IMPEDANCE CHANGE OVER TIME?
As the amount of current is dependent on both voltage and impedance, and voltage is held constant, then alterations in current over time will be mainly due to changes in impedance. This has been shown experimentally by studying nonhuman primates using a scaled-down version of the human DBS lead (8). In the 7 days following implantation, electrode impedance progressively increases, resulting in less current delivered. After application of continuous stimulation through the DBS electrode,
DOES THE USE OF CONSTANT CURRENT IMPACT CLINICAL OUTCOMES?
The data available in the literature suggest that impedance changes immediately following DBS implantation but then seems to stabilize. The amount of stimulation (i.e. current), however, will vary during initial activation and DBS programming, even when the voltage setting is not changed. Impedance can also change several months following DBS implantation, but it is unknown whether these changes are clinically relevant. To address this concern, Dr. Zvi Israel performed a small pilot study
CONCLUSIONS
There has been little reporting of constant-current DBS devices in movement and neuropsychiatric disorders; however, clinicians treating other neurological disorders (e.g., epilepsy) have already embraced the technology. As impedance varies considerably between patients and over time and there can be encapsulation, it makes sense that all new devices will likely use constant current. It is unlikely, given the potential benefits of constant-current devices, that we will observe many head-to-head
Authorship Statements
Drs. Bronstein, Tagliati, and Wertheimer conceived and organized the consensus conference and formed the agenda, and all authors participated in discussions at the meeting. Dr. Bronstein prepared the first draft of the manuscript, and all authors reviewed, critiqued, and approved of the final version.
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2021, Revue NeurologiqueCitation Excerpt :The present study is, to our knowledge, the second having analyzed the practical issues of the replacement of CV-nrIPG by a CC-rIPG in PD. CC stimulation reduces current fluctuations seen with CV stimulation [18], which are directly related to impedances variations [19]. This difference is thought to bring some benefits in terms of clinical outcome, but only one study has assessed the effect of switching from CC to CV stimulation in movement disorders, and it only included 13 PD patients [14].
Innovations in deep brain stimulation in aging: A focus on Parkinson disease
2021, Assessments, Treatments and Modeling in Aging and Neurological Disease: The Neuroscience of Aging
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Source of financial support: This paper was composed as a result of a consensus meeting in Princeton, NJ, on March 20, 2012, sponsored by the Parkinson Alliance.