Kilohertz frequency alternating current (KHFAC) waveforms reversibly block conduction in mammalian peripheral nerves. The initiation of the KHFAC produces nerve activation, called the onset response, ...before complete block occurs. An amplitude ramp, starting from zero amplitude, is ineffective in eliminating this onset activity. We postulated that initiating the ramp from a non-zero amplitude would produce a different effect on the onset.
Experiments were conducted in an in vivo rat model. KHFAC was applied at supra block threshold amplitudes and then reduced to a lower sub block amplitude (25, 50, 75 and 90% of the block threshold amplitude). The amplitude was then increased again to the original supra block threshold amplitude with an amplitude ramp. This ramp time was varied for each of the amplitude levels tested.
The amplitude ramp was successful in eliminating a second onset. This was always possible for the ramps up from 75 and 90% block threshold amplitude, usually from 50% but never from 25% of the block threshold amplitude.
This maneuver can potentially be used to initiate complete nerve block, transition to partial block and then resume complete block without producing further onset responses.
High-frequency alternating current (AC) waveforms have been shown to produce a quickly reversible nerve block in animal models, but the parameters and mechanism of this block are not well understood. ...A frog sciatic nerve/gastrocnemius muscle preparation was used to examine the parameters for nerve conduction block in vivo, and a computer simulation of the nerve membrane was used to identify the mechanism for block. The results indicated that a 100% block of motor activity can be accomplished with a variety of waveform parameters, including sinusoidal and rectangular waveforms at frequencies from 2 kHz to 20 kHz. A complete and reversible block was achieved in 34 out of 34 nerve preparations tested. The most efficient waveform for conduction block was a 3-5 kHz constant-current biphasic sinusoid, where block could be achieved with stimulus levels as low as 0.01 microCphase(-1). It was demonstrated that the block was not produced indirectly through fatigue. Computer simulation of high-frequency AC demonstrated a steady-state depolarisation of the nerve membrane, and it is hypothesised that the conduction block was due to this tonic depolarisation. The precise relationship between the steady-state depolarisation and the conduction block requires further analysis. The results of this study demonstrated that high-frequency AC can be used to produce a fast-acting, and quickly reversible nerve conduction block that may have multiple applications in the treatment of unwanted neural activity.
Electrical currents can be used to produce a block of action potential conduction in whole nerves. This block has a rapid onset and reversal. The mechanism of electrical nerve conduction block has ...not been conclusively determined, and inconsistencies appear in the literature regarding whether the block is produced by membrane hyperpolarization, depolarization, or through some other means. We have used simulations in a nerve membrane model, coupled with in vivo experiments, to identify the mechanism and principles of electrical conduction block. A nerve simulation package (Neuron) was used to model direct current (dc) block in squid, frog, and mammalian neuron models. A frog sciatic nerve/gastrocnemius preparation was used to examine nerve conduction block in vivo. Both simulations and experiments confirm that depolarization block requires less current than hyperpolarization block. Dynamic simulations suggest that block can occur under both the real physical electrode as well as adjacent virtual electrode sites. A hypothesis is presented which formulates the likely types of dc block and the possible block current requirements. The results indicate that electrical currents generally produce a conduction block due to depolarization of the nerve membrane, resulting in an inactivation of the sodium channels.
•The block inception time for kiloHertz frequency alternating current nerve block has not been measured previously.•A novel method was created to extract the block inception time from muscle force ...measurements.•The block inception time was found to be on average 5 ms to 10 ms, with the most rapid inception being 2.5 ms to 5 ms.•Block inception times for KHFAC nerve block were significant more rapid than previously estimated.
Kilohertz frequency alternating currents (KHFAC) produce rapid nerve conduction block of mammalian peripheral nerves and have potential clinical applications in reducing nerve hyperactivity. However, there are no experimental measurements of the block inception time (BIT) for the complete block of mammalian motor axons, i.e. the time from the start of delivery of the KHFAC to the axons reaching a fully blocked state.
A “counted cycles” method (CCM) was designed to exploit characteristics of the onset response, which is typical of KHFAC block, to measure the BIT with a millisecond time resolution. Randomized and repeated experiments were conducted in an in-vivo rodent model, using trains of KHFAC over a range of complete cycle counts at three frequencies (10, 20, and 40 kHz).
Complete motor nerve conduction block was obtained in the rat sciatic nerve (N = 4) with an average BIT range of 5 ms–10 ms. The fastest BIT measured was 2.5 ms–5 ms. There was no statistical difference between the block inception times for the three frequencies tested.
There are no comparable methods to measure the KHFAC BIT.
The KHFAC BIT is faster than previously estimated. KHFAC motor nerve block is established in milliseconds. These results may assist in the design of methods to eliminate the onset response produced by KHFAC nerve block.
The increase in global migration and the prioritization of English as an international language have resulted in science learning environments that include students whose primary language differs ...from the language of instruction. This worldwide phenomenon is not limited to geographical regions but occurs where diverse populations representing languages, cultures, ethnicities, and nationalities exist. English Language Learners (ELLs) in these classrooms face the task of learning science while learning to comprehend and participate in the discourse of science. Science teachers must therefore be strategic in providing experiences that will facilitate the development of ELLs’ literacy skills to do and engage science learning. We present how one middle school science teacher, engaging in practitioner inquiry, tapped into the potential of deliberate cognate instruction to support the learning of science vocabulary within the context of inquiry-based science teaching. The 7th grade teacher adapted a graphic organizer that served to focus on ELLs learning core ideas and through deliberate cognate instruction connected their Spanish language to English. Cognates, in conjunction with other teaching strategies, proved to be an effective way for the simultaneous learning of disciplinary content knowledge and vocabulary words. The knowledge generated from this practitioner inquiry had immediate impact and though not generalizable can offer insights beyond this immediate classroom. The Spanish-English cognate was a viable tool in bridging the language differences; however, we acknowledge that limitations will occur in classrooms where the languages may not have common roots to support cognate instructions.
To evaluate an implanted neuroprosthesis that allows tetraplegic users to control grasp and release in 1 hand.
Multicenter cohort trial with at least 3 years of follow-up. Function for each ...participant was compared before and after implantation, and with and without the neuroprosthesis activated.
Tertiary spinal cord injury (SCI) care centers, 8 in the United States, 1 in the United Kingdom, and 1 in Australia.
Fifty-one tetraplegic adults with C5 or C6 SCIs.
An implanted neuroprosthetic system, in which electric stimulation of the grasping muscles of 1 arm are controlled by using contralateral shoulder movements, and concurrent tendon transfer surgery. Assessed participants' ability to grasp, move, and release standardized objects; degree of assistance required to perform activities of daily living (ADLs), device usage; and user satisfaction.
Pinch force; grasp and release tests; ADL abilities test and ADL assessment test; and user satisfaction survey.
Pinch force was significantly greater with the neuroprosthesis in all available 50 participants, and grasp-release abilities were improved in 49. All tested participants (49/49) were more independent in performing ADLs with the neuroprosthesis than they were without it. Home use of the device for regular function and exercise was reported by over 90% of the participants, and satisfaction with the neuroprosthesis was high.
The grasping ability provided by the neuroprosthesis is substantial and lasting. The neuroprosthesis is safe, well accepted by users, and offers improved independence for a population without comparable alternatives.
An implantable, stimulated-muscle-powered piezoelectric active energy harvesting generator was previously designed to exploit the fact that the mechanical output power of muscle is substantially ...greater than the electrical power necessary to stimulate the muscle's motor nerve. We reduced to practice the concept by building a prototype generator and stimulator. We demonstrated its feasibility in vivo, using rabbit quadriceps to drive the generator. The generated power was sufficient for self-sustaining operation of the stimulator and additional harnessed power was dissipated through a load resistor. The prototype generator was developed and the power generating capabilities were tested with a mechanical muscle analog. In vivo generated power matched the mechanical muscle analog, verifying its usefulness as a test-bed for generator development. Generator output power was dependent on the muscle stimulation parameters. Simulations and in vivo testing demonstrated that for a fixed number of stimuli/minute, two stimuli applied at a high frequency generated greater power than single stimuli or tetanic contractions. Larger muscles and circuitry improvements are expected to increase available power. An implanted, self-replenishing power source has the potential to augment implanted battery or transcutaneously powered electronic medical devices.
A quick‐acting, quick‐reversing method for blocking action potentials in peripheral nerves could be used in the treatment of muscle spasticity and pain. A high‐frequency alternating‐current (HFAC) ...sinusoidal waveform is one possible means for providing this type of block. HFAC was used to block peripheral motor nerve activity in an in vivo mammalian model. Frequencies from 10 to 30 kHZ at amplitudes of between 2 and 10 V were investigated. A complete and reversible motor block was obtained at all frequencies. The block threshold amplitudes showed a linear relationship with frequency, the lowest threshold being at 10 kHZ. HFAC block has three phases: an onset response; a period of asynchronous firing; and a steady state of complete or partial block. The onset response and the asynchronous firing can be minimized by using an optimal frequency–amplitude combination. In general, the onset response was lowest for the combination of 30 kHZ and 10 V. Muscle Nerve, 2005
Neurotechnology has made major advances in development of interfaces to the nervous system that restore function in paralytic disorders. These advances enable both restoration of voluntary function ...and activation of paralyzed muscles to reanimate movement. The technologies used in each case are different, with external surface stimulation or percutaneous stimulation generally used for restoration of voluntary function, and implanted stimulators generally used for neuroprosthetic restoration. The opportunity to restore function through neuroplasticity has demonstrated significant advances in cases where there are retained neural circuits after the injury, such as spinal cord injury and stroke. In cases where there is a complete loss of voluntary neural control, neural prostheses have demonstrated the capacity to restore movement, control of the bladder and bowel, and respiration and cough. The focus of most clinical studies has been primarily toward activation of paralyzed nerves, but advances in inhibition of neural activity provide additional means of addressing the paralytic complications of pain and spasticity, and these techniques are now reaching the clinic. Future clinical advances necessitate having a better understanding of the underlying mechanisms, and having more precise neural interfaces that will ultimately allow individual nerve fibers or groups of nerve fibers to be controlled with specificity and reliability. While electrical currents have been the primary means of interfacing to the nervous system to date, optical and magnetic techniques under development are beginning to reach the clinic, and provide great opportunity. Ultimately, techniques that combine approaches are likely to be the most effective means for restoring function, for example combining regeneration and neural plasticity to maximize voluntary activity, combined with neural prostheses to augment the voluntary activity to functional levels of performance. It is a substantial challenge to bring any of these techniques through clinical trials, but as each of the individual techniques is sufficiently developed to reach the clinic, these present great opportunities for enabling patients with paralytic disorders to achieve substantial independence and restore their quality of life.
The feasibility of using the EEG signal to operate a hand grasp neuroprosthesis was investigated. Two able-bodied subjects and one neuroprosthesis user were trained to control the amplitude of the ...beta rhythm recorded over the frontal areas. After 6 months, all subjects exhibited a high level of control, being able to use this signal to move a cursor to targets on a computer screen with a high (>90%) accuracy rate. Control over the EEG signal was unaffected by upper extremity movement or electrical activation of the muscles, indicating that this signal would be adequate for neuroprosthetic use. To test this concept, the neuroprosthesis user operated his system with the cortical signal, and was able to effectively manipulate several objects.
PDF
