Wide-pulse electrical stimulation of the quadriceps allows greater maximal evocable torque than conventional stimulation

PURPOSE

The effectiveness of a neuromuscular electrical stimulation (NMES) program has been shown to be proportional to the maximal evocable torque (MET), which is potentially influenced by pulse characteristics such as duration and frequency. The aim of this study was to compare MET between conventional and wide-pulse NMES at two different frequencies.

METHODS

MET-expressed as a percentage of maximal voluntary contraction (MVC) torque-and maximal tolerable current intensity were quantified on 71 healthy subjects. The right quadriceps was stimulated with three NMES protocols using different pulse duration/frequency combinations: conventional NMES (0.2 ms/50 Hz; CONV), wide-pulse NMES at 50 Hz (1 ms/50 Hz; WP50) and wide-pulse NMES at 100 Hz (1 ms/100 Hz; WP100). The proportion of subjects reaching the maximal stimulator output (100 mA) before attaining maximal tolerable current intensity was also quantified.

RESULTS

The proportion of subjects attaining maximal stimulator output was higher for CONV than WP50 and WP100 (p < 0.001). In subjects who did not attain maximal stimulator output in any protocol, MET was higher for both WP50 and WP100 than for CONV (p < 0.001). Maximal tolerable current intensity was lower for both WP50 and WP100 than for CONV and was also lower for WP100 than for WP50 (p < 0.001).

CONCLUSION

When compared to conventional NMES, wide-pulse protocols resulted in greater MET and lower maximal tolerable current intensity. Overall, this may lead to better NMES training/rehabilitation effectiveness and less practical issues associated with maximal stimulator output limitations.

Feasibility and optimal choice of stimulation parameters for supramaximal stimulation of motor evoked potentials

PURPOSE

The aim was to investigate the feasibility and optimal stimulation parameters for supramaximal stimulation of muscle recorded transcranial electrical stimulation motor evoked potentials (mTc-MEP).

METHODS

Forty-seven consecutive patients that underwent scoliosis surgery were included. First, the feasibility of supramaximal stimulation was assessed for two settings (setting 1: pulse duration 0.075ms, interstimulus interval (ISI) 1.5ms; setting 2: pulse duration 0.300ms, ISI 3ms). Thereafter, three mTc-MEP parameters were considered for both settings; (1) elicitability, (2) amplitude, and (3) if supramaximal stimulation was achieved with ≥ 20 V below maximum output. Finally, ISIs (1ms-4ms) were optimized for setting 1.

RESULTS

Nine patients (19.15%) were excluded. Of the remaining patients, supramaximal stimulation was achieved in all patients for setting 1, and in 26 (68.42%) for setting 2. In one patient, mTc-MEPs were elicitable in more muscles for setting (1) Amplitudes were not significantly different. Stimulation voltage could be increased ≥ 20 V in all 38 patients for setting 1 and in 10 (38.46%) for setting (2) Optimal ISI's differed widely.

CONCLUSION

We recommend using setting 1 when monitoring mTc-MEPs with supramaximal stimulation, after which an individualized ISI optimization can be performed. Moreover, when using supramaximal stimulation, short ISI's (i.e. 1ms or 1.5ms) can be the optimal ISI for obtaining the highest mTc-MEP amplitude.

Effect of Different Pulse Durations on the Efficacy of Long-Pulsed Alexandrite-Assisted Hair Removal; A Split-Face Comparison Study

Introduction: Laser-assisted hair removal is widely used by a large number of patients complaining of unwanted hair. However, little is known about the effect of varying the pulse duration on clinical results and side effects. This study aimed to investigate the effectiveness of hair removal using an alexandrite laser with different pulse durations. Methods: Fifty female patients with facial hirsutism were subjected to a hair removal procedure with an alexandrite laser, using 3 and 10 milliseconds pulse durations on each side of the face every 5 weeks for three sessions. Photographs were taken and hair counts were checked before the treatment and one month postoperatively. Results: one month after the laser treatment, the clearance rate was 56% with both 3 and 10 milliseconds pulse durations. There was not any significant difference in clinical efficacy or the side effect profile. Conclusion: Using a 755 nm alexandrite laser for hair removal is an effective and safe method for delaying hair regrowth and this delay is not markedly different by increasing the pulse duration from 3 to 10 milliseconds.

Influence of Er:YAG laser pulse duration on the long-term stability of organic matrix and resin-dentin interface

The purpose of this study was to explore the influence of Er:YAG laser irradiation with different pulse durations on the organic matrix, micromorphology of the hybrid layer (HL), and bond strength over time. Sixty caries-free human molars were cut to obtain flat dentin surfaces which were randomly divided into 4 groups: control (not irradiated-G1) and laser groups (80 mJ/2 Hz) with pulse duration ranging between 50 (G2), 300 (G3), and 600 μs (G4). A self-etch adhesive system (Universal 3M ESPE) was applied on pre-treated dentin surfaces and cylinders of resin composite were built up and stressed in a universal testing machine (μSBS) at 24 h and after12 months (n = 12). In addition, 3 other dentin-bonded specimens were prepared as previously described for each group with the adhesive doped with 0.1 wt% Rhodamine B to analyze hybrid layer morphology under Confocal Laser Microscope Scanning (CLMS). Organic matrix and collagen fibrils were analyzed by second harmonic generation (SGH). Two-way ANOVA and Tukey's test detected significantly higher μSBS values for the control group, whereas the lower values were observed in all laser groups at 24 h (p < 0.05). Storage in artificial saliva did not reduce μSBS in all groups. The low signal emitted by SHG images below the irradiated area demonstrated thermal damage of the collagen matrix. CLMS images of laser groups exhibited thicker and irregular resin-dentin interfaces than the control group. Regardless of the pulse duration, Er:YAG laser pre-treatment altered the organic matrix and HL formation which resulted in low μSBS values at 24 h. The alterations on dentin's organic structure did not jeopardize the μSBS after 1 year of saliva storage.

Pulse Duration as Well as Current Direction Determines the Specificity of Transcranial Magnetic Stimulation of Motor Cortex during Contraction

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Selective stimulation of inputs to corticospinal neurons may be achieved by manipulating current direction and pulse duration.

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Neural populations recruited by brief (30 μs) anterior–posterior currents exhibited the greatest sensitivity to somatosensory input.

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Pulse duration is an important determinant of what is activated with TMS in human motor cortex.

Background

Previous research suggested that anterior–posterior (AP) directed currents induced by TMS in motor cortex (M1) activate interneuron circuits different from those activated by posterior–anterior currents (PA). The present experiments provide evidence that pulse duration also determines the activation of specific interneuron circuits.

Objective

To use single motor unit (SMU) recordings to confirm the difference in onset latencies of motor-evoked potentials (MEPs) evoked by different current directions and pulse durations: AP₃₀, AP₁₂₀, PA₃₀ and PA₁₂₀. To test whether the amplitude of the MEPs is differentially influenced by somatosensory inputs from the hand (short-latency afferent inhibition, SAI), and examine the sensitivity of SAI to changes in cerebellar excitability produced by direct current stimulation (tDCS_Cb).

Methods

Surface electromyograms and SMUs were recorded from the first dorsal interosseous muscle. SAI was tested with an electrical stimulus to median or digital nerves ~20–25 ms prior to TMS delivered over the M1 hand area via a controllable pulse parameter TMS (cTMS) device. SAI was also tested during the application of anodal or sham tDCS_Cb. Because TMS pulse specificity is greatest at low stimulus intensities, most experiments were conducted with weak voluntary contraction to reduce stimulus threshold.

Results

AP₃₀ currents recruited the longest latency SMU and surface MEP responses. During contraction SAI was greater for AP₃₀ responses versus all other pulses. Online anodal tDCS_Cb reduced SAI for the AP₃₀ currents only.

Conclusions

AP₃₀ currents activate an interneuron circuit with functional properties different from those activated by other pulse types. Pulse duration and current direction determine what is activated in M1 with TMS.

Systematic evaluation of a holmium:yttrium-aluminum-garnet laser lithotripsy device with variable pulse peak power and pulse duration

OBJECTIVE

The Holmium:yttrium-aluminum-garnet (Ho:YAG) laser is the standard lithotrite for ureteroscopy. This paper is to evaluate a Ho:YAG laser with a novel effect function in vitro, which allows a real-time variation of pulse duration and pulse peak power.

METHODS

Two types of phantom calculi with four degrees of hardness were made for fragmentation and retropulsion experiments. Fragmentation was analysed at 5 (0.5 J/10 Hz), 10 (1 J/10 Hz), and 20 (2 J/10 Hz) W in non-floating phantom calculi, retropulsion in an ureteral model at 10 (1 J/10 Hz) and 20 (2 J/10 Hz) W using floating phantom calculi. The effect function was set to 25%, 50%, 75%, and 100% of the maximum possible effect function at each power setting. Primary outcomes: fragmentation (mm3), the distance of retropulsion (cm); ≥5 measurements for each trial.

RESULTS

An increase of the effect feature (25% vs. 100%), i.e., an increase of pulse peak power and decrease of pulse duration, improved Ho:YAG laser fragmentation. This effect was remarkable in soft stone composition, while there was a trend for improved fragmentation with an increase of the effect feature in hard stone composition. Retropulsion increased with increasing effect function, independently of stone composition. The major limitations of the study are the use of artificial stones and the in vitro setup.

CONCLUSION

Changes in pulse duration and pulse peak power may lead to improved stone fragmentation, most prominently in soft stones, but also lead to increased retropulsion. This new effect function may enhance Ho:YAG laser fragmentation when maximum power output is limited or retropulsion is excluded.