Novel clinical treatments to target peripheral nerves are being developed which primarily use electrical current. Recently, infrared (IR) light was shown to inhibit peripheral nerves with high spatial and temporal specificity. Here, for the first time, we demonstrate that IR can selectively and reversibly inhibit small-diameter axons at lower radiant exposures than large-diameter axons. We provide a mathematical rationale, and then demonstrate it experimentally in individual axons of identified neurons in the marine mollusk Aplysia californica, and in axons within the vagus nerve of a mammal, the musk shrew Suncus murinus. The ability to selectively, rapidly, and reversibly control small-diameter sensory fibers may have many applications, both for the analysis of physiology, and for treating diseases of the peripheral nervous system, such as chronic nausea, vomiting, pain, and hypertension. Moreover, the mathematical analysis of how IR affects the nerve could apply to other techniques for controlling peripheral nerve signaling.

Abstract. Nerve block can eliminate spasms and chronic pain. Kilohertz frequency alternating current (KHFAC) produces a safe and reversible nerve block. However, KHFAC-induced nerve block is associated with an undesirable onset response. Optical inhibition using infrared (IR) laser light can produce nerve block without an onset response, but heats nerves. Combining KHFAC with IR inhibition [alternating current and infrared (ACIR)] produces a rapidly reversible nerve block without an onset response. ACIR can be used to rapidly and reversibly provide onset-free nerve block in the unmyelinated nerves of the marine mollusk Aplysia californica and may have significant advantages over either modality alone. ACIR may be of great clinical utility in the future. © The Authors. Published by SPIE under a Creative Commons Attribution 3.0 Unported License. Distribution or reproduction of this work in whole or in part requires full attribution of the original publication, including its DOI.

BACKGROUND AND PURPOSE There is a lack of consensus in the literature as to which body habitus parameter most influences nerve cross‐sectional area (CSA). This study was specifically designed to determine if height or weight is more influential. METHODS Fifteen young healthy participants, 8 extremely tall and 7 heavy, with no peripheral nerve symptoms were recruited. The tall cohort consisted of males who were 74 inches or taller and females who were 68 inches or taller. The heavy cohort consisted of males who were 274 lbs or heavier and females who were 200 lbs or heavier. Measurements were obtained bilaterally at 7 sites using neuromuscular ultrasound: median nerve at the wrist and mid‐forearm, ulnar at the elbow, radial at the spiral groove, fibular at the knee, tibial at the ankle, and sural at the ankle. The nerve CSA at each site was measured by tracing of the nerve using the “freehand” trace function of the ultrasound device. RESULTS Weight tightly correlated with nerve CSA (R2 = .69, P < .001), while height did not significantly predict CSA (R2 = .10, P = .244). Nerve CSA for tall participants did not systematically deviate from an historical control group. Conversely, with exception of the tibial and sural nerves at the ankle, all nerve CSAs for heavy participants were higher than in the control group. CONCLUSION Weight was found to be the body habitus parameter that most influences nerve CSA. This will inform clinicians when using nerve imaging to evaluate participants at either extreme of weight.

No abstract

No abstract