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Chapter 16 Electrophysiology
Published in B H Brown, R H Smallwood, D C Barber, P V Lawford, D R Hose, Medical Physics and Biomedical Engineering, 2017
There is one situation where a relatively large sensory nerve action potential is obtained and this can be useful for demonstration and teaching purposes. Following stimulation of the median nerve at the wrist, nerve impulses will be conducted in both directions along the nerve fibres; conduction up the sensory nerves in the normal direction is termed orthodromic conduction and conduction in the opposite direction is called antidromic conduction. Antidromic conduction gives rise to quite a large nerve action potential if recording electrodes are placed around the base of the index finger and a stimulus applied to the median nerve at the wrist. This signal can be recorded without a signal averager and should have a latency of about 5 ms to the peak of the action potential.
Deep brain stimulation programming strategies: segmented leads, independent current sources, and future technology
Published in Expert Review of Medical Devices, 2021
Bhavana Patel, Shannon Chiu, Joshua K. Wong, Addie Patterson, Wissam Deeb, Matthew Burns, Pamela Zeilman, Aparna Wagle-Shukla, Leonardo Almeida, Michael S. Okun, Adolfo Ramirez-Zamora
DBS involves applying an electrical field directly into a brain region and modulating connected circuitry. DBS may lead to the opening and closing of voltage-gated sodium channels and subsequent propagation of orthodromic or antidromic action potentials, ultimately affecting the release of neurotransmitters [19,20]. The clinical benefits of DBS are well known, however the time course ranges from seconds to minutes (i.e., tremor suppression) to weeks to months (i.e., improvement in dystonia, tics, obsessive-compulsive disorder). This variability in time course suggests multiple biological changes and potential mechanisms of action. It may also infer that we may not have achieved the most efficient form of stimulation for specific disorders or symptoms [20–22]. Since its introduction, the exact mechanism of action of DBS has been elusive, although several hypotheses have been proposed. We will summarize some of the most common hypotheses.
A novel fast-acting sub-perception spinal cord stimulation therapy enables rapid onset of analgesia in patients with chronic pain
Published in Expert Review of Medical Devices, 2021
Clark S. Metzger, M. Blake Hammond, Jose F. Paz-Solis, William J. Newton, Simon J. Thomson, Yu Pei, Roshini Jain, Michael Moffitt, Luca Annecchino, Que Doan
Paresthesia-based spinal cord stimulation (SCS) has been used for decades to treat chronic pain. Historically, antidromic activation of the nerve fibers in the dorsal columns has been thought by some to be capable of ‘closing the gate’ resulting in analgesia, while orthodromic activation elicits paresthesias [1]. The relationship between the induction of paresthesia and analgesia was therefore assumed to be linked given that the location of pain relief has been demonstrated to correlate with paresthesia overlap [2]. However, nearly 40 years after the inception of SCS, Yearwood, and Foster described SCS cases wherein analgesia was achieved at amplitudes below the paresthesia threshold, and current SCS approaches now exist that do not produce paresthesia, variously described as ‘paresthesia-free’, ‘paresthesia-independent’, or ‘sub-perception’ SCS [3–6]. Intriguingly, sub-perception SCS yields a slower onset of analgesia after turning on stimulation (typically several hours to days) in contrast to paresthesia-based SCS in which analgesia is usually observed within minutes [7–10]. This has contributed to various hypotheses regarding potential mechanisms of action that mediate pain relief produced by sub-perception-based approaches [10–12].
Burst and high frequency stimulation: underlying mechanism of action
Published in Expert Review of Medical Devices, 2018
Shaheen Ahmed, Thomas Yearwood, Dirk De Ridder, Sven Vanneste
SCS is being used to treat neuropathic pain, failed back surgery syndrome (FBSS), complex regional pain syndrome (CRPS), angina pectoris, and ischemic limb pain [10–12]. SCS is advantageous in part because it is minimally invasive, making it a safer and more cost-effective technique than surgical methods. Furthermore, SCS can achieve targeted pain relief and even reduce opioid use, all with little to no side effects [13]. Traditionally, SCS therapy is delivered via tonic stimulation, usually with a frequency between 40 and 50 Hz, an amplitude between 2 and 4 mA, and a pulse width that falls between 300 and 500 µs. The mechanism of action of SCS can be understood through both spinal and supraspinal mechanisms [14,15]. Electrical stimulation produces both orthodromic and antidromic action potentials. The action potential travels antidromically into the dorsal horn, where Aβ fibers synapse with the wide-dynamic-range neurons and release inhibitory neurotransmitters such as γ-amino butyric acid (GABA) and adenosine. The orthodromic potentials travel to the dorsal column, inducing inhibition via serotonergic and noradrenergic pathways [16,17].