Posts Tagged Pulse width

[BLOG POST] Understanding the factors that impact the effectiveness of Functional Electrical Stimulation (FES) – pulse width and charge & torque

In the final of a series of blog articles, we are going to look at the factors that impact the effectiveness of FES. This one covers pulse width and charge & torque.

Read the first article here

Read the second article here

Pulse width

The available pulse widths in FES devices vary, most commonly between 150 and 300us, however much wider variations (50us to 2500us) in pulse width can have differing effects upon the target muscle tissue.

Practically, a longer pulse width causes the stimulus to remain in the tissues for longer, depolarising a greater number of nerve fibres, indiscriminate of motor, sensory or pain. Higher pulse widths have been shown to generate greater levels of torque and can often allow tetanic muscle contractions resulting in physiological joint movement at lower levels of amplitude, which can be useful when attempting to maximise torque in those with intact sensation.

However, when looking for a specific muscle contraction, for example a bicep’s, if too great a pulse width is applied it is common to see overflow into surrounding or opposing muscle groups. Compared to pulse frequency and current amplitude, the role of pulse duration is less appreciated in its possible influence on maximising torque output.

Alon et al back in 1983 showed that motor stimulation could be achieved with pulse durations in the range of 20 to 200 microseconds, without stimulation of pain response. In contrast, Hultman et al (1983) showed that a pulse duration of 500 microseconds resulted in 40% greater torque output compared to 150 microseconds.

Moreover, a pulse duration of 450 microseconds has been shown to be effective in conducting electrically induced resistance training in individuals with spinal cord injury (Kendell et al., 2006, Burnham et al., 1997, cited by Dolbow and Gorgey, 2016).

However, despite this evidence, most researchers have used pulse durations of 300 microseconds or below in their studies, which could potentially limit the outcome of Neuromuscular Electric Stimulation (NMES) protocols in maximising elicited torque output. The controversy regarding pulse duration selection reflects the limited amount of knowledge regarding the optimal pulse duration required to maximise torque output.

Charge & Torque

Total charge, the product of combined amplitude and pulse width, determines the force produced from the resultant muscle contraction. Maximising the charge, by applying maximal amplitude and pulse width, is likely to result in the maximum torque.

However, as stated above, patient tolerance is the determinant of how much charge may be applied. Manipulating both amplitude and pulse width can help to generate sufficient charge to result in a forceful muscle contraction, without becoming unbearable for the patient.

This article is taken from our white paper “The integration of Functional Electrical Stimulation (FES) technology and neurorehabilitation”.

via Understanding the factors that impact the effectiveness of Functional Electrical Stimulation (FES) – pulse width and charge & torque | Cyclone

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[Abstract] The interaction of pulse width and current intensity on the extent of cortical plasticity evoked by vagus nerve stimulation.

Abstract

Background

Repeatedly pairing a tone with a brief burst of vagus nerve stimulation (VNS) results in a reorganization of primary auditory cortex (A1). The plasticity-enhancing and memory-enhancing effects of VNS follow an inverted-U response to stimulation intensity, in which moderate intensity currents yield greater effects than low or high intensity currents. It is not known how other stimulation parameters effect the plasticity-enhancing effects of VNS.

Objective

We sought to investigate the effect of pulse-width and intensity on VNS efficacy. Here, we used the extent of plasticity induced by VNS-tone pairing to assess VNS efficacy.

Methods

Rats were exposed to a 9 kHz tone paired to VNS with varying current intensities and pulse widths. Cortical plasticity was measured as changes in the percent of area of primary auditory cortex responding to a range of sounds in VNS-treated rats relative to naïve rats.

Results

We find that a combination of low current intensity (200 μA) and short pulse duration (100 μs) is insufficient to drive cortical plasticity. Increasing the pulse duration to 500 μs results in a reorganization of receptive fields in A1 auditory cortex. The extent of plasticity engaged under these conditions is less than that driven by conditions previously reported to drive robust plasticity (800 μA with 100 μs wide pulses).

Conclusion

These results suggest that the plasticity-enhancing and memory-enhancing effects of VNS follow an inverted-U response of stimulation current that is influenced by pulse width. Furthermore, shorter pulse widths may offer a clinical advantage when determining optimal stimulation current. These findings may facilitate determination of optimal VNS parameters for clinical application.

via The interaction of pulse width and current intensity on the extent of cortical plasticity evoked by vagus nerve stimulation – Brain Stimulation: Basic, Translational, and Clinical Research in Neuromodulation

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