Remote Electrical Stimulation by Means of Implanted Rectifiers

Miniaturization of active implantable medical devices is currently compromised by the available means for electrically powering them. Most common energy supply techniques for implants – batteries and inductive couplers – comprise bulky parts which, in most cases, are significantly larger than the circuitry they feed. Here, for overcoming such miniaturization bottleneck in the case of implants for electrical stimulation, it is proposed to make those implants act as rectifiers of high frequency bursts supplied by remote electrodes. In this way, low frequency currents will be generated locally around the implant and these low frequency currents will perform stimulation of excitable tissues whereas the high frequency currents will cause only innocuous heating. The present study numerically demonstrates that low frequency currents capable of stimulation can be produced by a miniature device behaving as a diode when high frequency currents, neither capable of thermal damage nor of stimulation, flow through the tissue where the device is implanted. Moreover, experimental evidence is provided by an in vivo proof of concept model consisting of an anesthetized earthworm in which a commercial diode was implanted. With currently available microelectronic techniques, very thin stimulation capsules (diameter <500 µm) deliverable by injection are easily conceivable

Microstructural analysis of deformation-induced hypoxic damage in skeletal muscle

Deep pressure ulcers are caused by sustained mechanical loading and involve skeletal muscle tissue injury. The exact underlying mechanisms are unclear, and the prevalence is high. Our hypothesis is that the aetiology is dominated by cellular deformation (Bouten et al. in Ann Biomed Eng 29:153–63, 2001; Breuls et al. in Ann Biomed Eng 31:1357–364, 2003; Stekelenburg et al. in J App Physiol 100(6):1946–954, 2006) and deformation-induced ischaemia. The experimental observation that mechanical compression induced a pattern of interspersed healthy and dead cells in skeletal muscle (Stekelenburg et al. in J App Physiol 100(6):1946–954, 2006) strongly suggests to take into account the muscle microstructure in studying damage development. The present paper describes a computational model for deformation-induced hypoxic damage in skeletal muscle tissue. Dead cells stop consuming oxygen and are assumed to decrease in stiffness due to loss of structure. The questions addressed are if these two consequences of cell death influence the development of cell injury in the remaining cells. The results show that weakening of dead cells indeed affects the damage accumulation in other cells. Further, the fact that cells stop consuming oxygen after they have died, delays cell death of other cells

Effects of electrical stimulation-induced gluteal versus gluteal and hamstring muscles activation on sitting pressure distribution in persons with a spinal cord injury

Study design:Ten participants underwent two electrical stimulation (ES) protocols applied using a custom-made electrode garment with built-in electrodes. Interface pressure was measured using a force-sensitive area. In one protocol, both the gluteal and hamstring (gh) muscles were activated, in the other gluteal (g) muscles only.Objectives:To study and compare the effects of electrically induced activation of gh muscles versus g muscles only on sitting pressure distribution in individuals with a spinal cord injury (SCI).Setting:Ischial tuberosities interface pressure (ITs pressure) and pressure gradient.Results:In all participants, both protocols of g and gh ES-induced activation caused a significant decrease in IT pressure. IT pressure after gh muscles activation was reduced significantly by 34.5% compared with rest pressure, whereas a significant reduction of 10.2% after activation of g muscles only was found. Pressure gradient reduced significantly only after stimulation of gh muscles (49.3%). gh muscles activation showed a decrease in pressure relief (Δ IT) over time compared with g muscles only.Conclusion:Both protocols of surface ES-induced of g and gh activation gave pressure relief from the ITs. Activation of both gh muscles in SCI resulted in better IT pressure reduction in sitting individuals with a SCI than activation of g muscles only. ES might be a promising method in preventing pressure ulcers (PUs) on the ITs in people with SCI. Further research needs to show which pressure reduction is sufficient in preventing PUs. © 2012 International Spinal Cord Society All rights reserved

Gluteal blood flow and oxygenation during electrical stimulation-induced muscle activation versus pressure relief movements in wheelchair users with a spinal cord injury

<p>Background: Prolonged high ischial tuberosities pressure (IT pressure), decreased regional blood flow (BF) and oxygenation (%SO2) are risk factors for developing pressure ulcers (PUs) in patients with spinal cord injury (SCI). Electrical stimulation (ES)-induced gluteal and hamstring muscle activation may improve pressure distribution by changing the shape of the buttocks while sitting and also increase BF and %SO2.</p><p>Objective: To compare acute effects of ES-induced gluteal and hamstring muscle activation with pressure relief movements (PRMs) on IT pressure, BF and %SO2.</p><p>Participants and methods: Twelve men with SCI performed PRMs - push-ups, bending forward and leaning sideward - and received surface ES (87 +/- 19 mA) to the gluteal and hamstring muscles while sitting in their wheelchair. Ischial tuberosities pressure was measured using a pressure mapping system; (sub) cutaneous BF and %SO2 were measured using reflection spectroscopy and laser Doppler, respectively.</p><p>Results: Compared with rest (156 +/- 26 mm Hg), IT pressure was significantly lower during all other conditions (push-ups 19 +/- 44; bending forward 56 +/- 33; leaning sideward 44 +/- 38; ES 67 +/- 45 mm Hg). For the whole group, all PRMs significantly augmented BF (+39 to -96%) and %SO2 (+6.0 to -7.9%-point), whereas ES-induced muscle activation did only for peak BF. In all, 63% of the participants showed an increased BF (average 52%) with ES.</p><p>Conclusion: PRMs acutely reduced IT pressure and improved oxygenation and BF in SCI. The currently used ES method cannot replace PRMs, but it may be used additionally. ES-induced muscle activation is not as effective for acute pressure relief, but the frequency of stimulation is much higher than the performance of PRMs and can therefore be more effective in the long term.</p>