An in silico analysis of neuromodulation for pain relief: Determining the role of classical electrodynamics.

There has been ongoing debate about the efficacy and mechanism of action of neuromodulation devices in pain relief applications. It has recently been suggested that both issues may be resolved if electromagnetic theory is incorporated into the understanding and application of this technology, and we therefore undertook an in silico analysis to further explore this idea. We created a CAD replication of a standard neuromodulation electrode array with a generic linear 3/6 mm 8-contact lead, developed a parameterized algorithmic model for the pulse delivered by the device and assigned material properties to biologic media to accurately reflect their electromagnetic properties. We then created a physical simulation of the device's output both in air and in the biophysical environment. The simulations confirmed the presence of an electromagnetic field (EM field). Variations in programming of the device affected the strength of the EM field by orders of magnitude. The biologic media all absorbed the EM field, an effect which was particularly pronounced in cerebrospinal fluid and muscle. We discuss the implications of all these findings in relation to the literature. We suggest that knowledge of electromagnetic theory and its application within the biophysical space is required for the optimal use of neuromodulation devices in pain relief applications.

On the Origin of Pain - the 'Pain Channel' Hypothesis.

Theories of pain have traditionally attributed the sensory experience of pain to the brain. We present here a new hypothesis on the origin of pain which is based on a novel approach to the management of persistent pain. We call it the 'pain channel' hypothesis of the origin of pain. There are key components to the development of our hypothesis: [1] Our clinical outcome of a persistently pain-free state, representing a maintained pain score of 0/10 has been achieved in a growing cohort of various presentations of persistent pain now exceeding 130 patients over the course of the last five years. With complete control of pain, the patients rapidly return to their premorbid state and level of function. This result requires careful consideration and explanation. [2] Regional anaesthesia has been used as a diagnostic tool to confirm the clinically suspected source of the persistent pain. The pharmacodynamics of local anaesthetics identify the sodium channel of the primary nociceptive sensory neuron as the critical subcellular structure generating pain. [3] Sodium channel function has been recognised as a bioelectromagnetic phenomenon. [4] Neuromodulation has been used to provide our long-term pain relief result. We understand the neuromodulation unit as producing an electromagnetic field within the super low wavelength range of the electromagnetic spectrum and we have devised a strategy which we believe delivers maximal electromagnetic field effect to the intended sodium channels to create a long-term conduction block. We believe that our clinical outcome challenges the current understanding of the role of the brain in pain. We hypothesise that pain is a peripheral phenomenon rather than being a construct of the brain, as our strategy is peripherally based and completely reverses the presenting clinical profile of persistent pain. More specifically we hypothesise that the sensory phenomenon of pain is a function of specific sodium channels which are coded for pain and which are part of the subcellular structure of peripheral nociceptive sensory nerves. We believe that these hypotheses can lead to a change in focus in the diagnosis and management of pain and drive improvement in current technology and medications to facilitate effective treatment of persistent pain.

Successful peripheral neuromodulation for phantom limb pain.

SETTING: For decades, the heterogeneity of the amputee population and the complex interaction of biopsychosocial factors have confounded researchers' attempts to develop an effective treatment for phantom limb pain. Therefore, it remains difficult to treat, and affected patients often experience decreased quality of life, increased psychological distress, and poorer health outcomes. PATIENT: In the case study, we report a novel strategy for the peripheral placement of neuromodulation leads for the treatment of phantom limb pain in a patient who subsequently described complete and consistent pain relief independent of significant variations in psychosocial stress.

The "axillary tunnel": an anatomic reappraisal of the limits and dynamics of spread during brachial plexus blockade.

BACKGROUND: Various anatomic factors have been described as affecting the distribution of a solution injected around the brachial plexus. Using computerized axial tomography dye studies, we introduce a new concept. METHODS: Ten patients with brachial plexus catheters sited using the bent needle supraclavicular technique were studied. After the catheter tip was located, 20 mL 50% diluted Omnipaque dye was injected through the catheter. The limits of spread of dye and patterns of dye distribution were described and quantified. RESULTS: The brachial plexus is contained within, and closely surrounded by, rigid muscular and bony boundaries, which effectively create a tunnel. Tunnel unit volumes are small (5.21-9.5 cm3), differing significantly from the volume of dye injected (P < 0.001), so spread must occur along the tunnel. Tunnel dimensions vary, with potential points of resistance at the apex of the axilla and in the subcoracoid region. Catheters placed for shoulder surgery, with tips located inferomedial to the medial edge of the coracoid process, were associated with 90% retrograde flow (95% C.I. = 83-97). Catheters placed for more distal surgical procedures, with tips located inferolateral to the medial edge of the coracoid process, were associated with equally antero- and retrograde flow. CONCLUSIONS: We conclude that the brachial plexus is contained within a rigid-walled tunnel of variable dimensions, which we call the "axillary tunnel." The scapula/subscapularis complex, related to the subcoracoid point of resistance, may account for the differing patterns of dye distribution observed.

Rectus sheath catheters for continuous analgesia after upper abdominal surgery.

The segmental nerves T6-T11 pass through and innervate the rectus abdominis muscle and overlying skin. The arcuate lines compartmentalize the rectus, but they are deficient posteriorly and hence a catheter tunnelled into the posterior sheath can be used to achieve an effective continuous analgesic block. Volume is important to fill the compartment. It is a simple surgical procedure that has several advantages and appears a viable alternative to epidural analgesia.

The sheath of the brachial plexus: fact or fiction?

BACKGROUND: The concept of the axillary "sheath" has been a central tenet of brachial plexus regional anesthesia for many years. Recent investigations have cast doubt on its nature and existence. This study further examines the issue. METHODS: Computerized axial tomographic dye studies were performed using continuous catheter systems for the sciatic nerve and the brachial plexus. The resultant images were compared and contrasted. RESULTS: The images of the two catheter systems were the same, with the exception that one was of the upper extremity and the other was of the lower extremity. CONCLUSIONS: The sciatic nerve is not surrounded or enveloped by a "sheath"--it lies in the tissue plane between rigid anatomical structures. Similarly, the brachial plexus lies in the tissue plane between the rigid anatomy of the chest wall, scapula, humerus, and pectoral fascia. This finding is inconsistent with the concept of the axillary sheath.

A magnetic resonance imaging analysis of the infraclavicular region: can brachial plexus depth be estimated before needle insertion?

In this study we examined the anatomy of the infraclavicular region to assess the possibility of estimating brachial plexus depth before performing an infraclavicular block, by using readily identifiable landmarks such as the coracoid process (CP) and the clavicle (CL). Four parasagittal planes across the infraclavicular region were analyzed in 21 individual series of magnetic resonance imaging studies. Measurements included distance to the plexus from the skin of the anterior chest wall, position of the plexus relative to the CL, and clavicular width. The brachial plexus is located directly below the CL in the parasagittal plane 1 cm medial to the CP. If one inserts a needle in this same plane at a point in line with the inferomedial edge of the CP, then plexus depth can be estimated as follows. If the needle is raised, as a whole, straight up from the planned point of insertion to be level with the top of the CL, then the distance from the tip of the needle to a point midway across the width of the CL is equivalent to the distance from the insertion point to the plexus. Furthermore, not only is it uncommon to find the lung in this same parasagittal plane, but when it does appear, it is well behind the plexus. Estimating plexus depth, or "depth gauging," in the infraclavicular region is achievable and is a potentially useful strategy. Further study is required to confirm this finding in the clinical environment.