Muscle force development after low‐frequency magnetic burst stimulation in dogs

Abstract

Introduction: Magnetic stimulation allows for painless and non‐invasive extrinsic motor nerve stimulation. Despite several advantages, the limited coupling to the target reduces the application of magnetic pulses in rehabilitation. According to experience with electrical stimulation, magnetic bursts could remove this constraint. Methods: A novel burst stimulator was used to apply single and burst pulses to the femoral nerve in 10 adult dogs. A figure‐of‐eight coil was connected, and pulses were applied at 7.5 HZ. Contractions of the quadriceps muscle were measured via an angle force transducer. Results: Muscle forces were significantly higher upon burst stimulation than after single pulses. Four consecutive burst pulses proved most effective. Stimulation by more bursts resulted in fatigue. Conclusion: Burst stimulation is superior to standard magnetic single pulses, and 4 consecutive burst pulses proved most effective. Muscle Nerve, 2012

Modular multilevel TMS device with wide output range and ultrabrief pulse capability for sound reduction

“…The relative loudness of the Gaussian envelope pulses is due to a significant low-frequency sideband of the squared coil current, which is the dominant driving factor for the coil sound. However, these comparisons may be confounded since the simplified neural depolarization model is not able to correctly estimate the threshold for polyphasic pulses [28,29,47,54]. Moreover, we did not optimize any parameters of the Gaussian pulses such as the width of the envelope.…”

“…As shown in figure 1(b), each module employs an H-bridge circuit [36], implemented with high-voltage, high-current insulated-gate bipolar transistor (IGBT) switches and appropriate snubber and gate drive circuits, following our approach for prior, simpler TMS device designs [8][9][10]29]. The module's output voltage, Vi, depends on the switches' states and is equal to VCi, 0, or −VCi, where VCi denotes the energy storage capacitor of module i.…”

“…The first-order lowpass filter was implemented with the filter function in MATLAB (The MathWorks, USA). However, this linear model may overestimate the stimulation strength of ultrabrief rectangular pulses as it neglects ion-channel dynamics [45,46], and underestimates the stimulation strength of polyphasic pulses [28,29,47]. Thus, the peak ΔVm value should be interpreted only as a rough approximation for the effective stimulation strength.…”

“…The capability of MM-TMS to generate relatively complex pulse shapes is illustrated in figure 10 with sinusoidal polyphasic pulses with a Gaussian envelope. Compared to a conventional polyphasic pulse with a flat envelope [28,29], these pulses reduce the subharmonic sideband in the spectrum of the coil current, which could improve the acoustic performance of polyphasic pulses, as discussed in the following sections.…”

“…matching or exceeding the duration of conventional TMS pulses, enabling, for example, the measurement of extended strength-duration curves [12,27]. Further, the modular topology provides 21 voltage levels within a pulse, allowing the generation of complex waveforms such as polyphasic (multicycle) pulses that can reduce the neural activation threshold and produce more robust motor evoked responses [28,29]. The polyphasic pulses can also be amplitude-modulated, for example, with a Gaussian envelope, which has a narrower frequency bandwidth and was suggested to reduce the acoustic spectral sidebands and therefore the audible acoustic noise if the dominant frequency is concurrently shifted above the upper hearing limit [22].…”