In what universe do you exist if you think your doctor is going to do anything with this? Or are they going to stop reading after the abstract and incorrectly assume this is only SCI?
Sum of phase-shifted sinusoids stimulation prolongs paralyzed muscle output
Abstract
Neuroprostheses
that activate musculature of the lower extremities can enable standing
and movement after paralysis. Current systems are functionally limited
by rapid muscle fatigue induced by conventional, non-varying stimulus
waveforms. Previous work has shown that sum of phase-shifted sinusoids
(SOPS) stimulation, which selectively modulates activation of individual
motor unit pools (MUPs) to lower the duty cycle of each while
maintaining a high net muscle output, improves joint moment maintenance
but introduces greater instability over conventional stimulation. In
this case study, implementation of SOPS stimulation with a real-time
feedback controller successfully decreased joint moment instability and
further prolonged joint moment output with increased stimulation
efficiency over open-loop approaches in one participant with spinal cord
injury. These findings demonstrate the potential for closed-loop SOPS
to improve functionality of neuroprosthetic systems.
Introduction
Paralysis
due to spinal cord injury (SCI), stroke, or other upper motor neuron
injury often leads to limited mobility and wheelchair dependence. The
resulting sedentary lifestyle has numerous negative health consequences
including muscle deconditioning, decreased bone density, poor
circulation, pressure injuries, and cardiovascular disease [1].
Weight-bearing standing exercise can address these health concerns,
allow those that are wheelchair dependent to obtain level eyesight with
their peers, and expand their sphere of interaction with the world.
Standing after upper motor neuron injury can be achieved with neural stimulation that activates the paralyzed musculature of the lower extremities [2, 3]. However, due to the rapid muscle fatigue commonly induced by extracellular stimulation [4, 5] and exacerbated by physiological changes after paralysis [6], standing times with current systems are limited and highly variable. In our laboratory, the median standing time for participants with SCI is three minutes [3], and similarly short durations have been reported by others despite various interventions for improvement [7,8,9,10]. These systems are therefore mainly beneficial for short duration tasks, such as transfers into and out of a wheelchair. Extending standing times would enable users of neuroprostheses to obtain greater physiological, functional, and social benefits from these systems.
Conventional approaches deliver non-varying stimulus current waveforms through multiple knee extensor-activating electrode contacts to ensure the joint remains locked and stable during standing. However, simultaneously activating many knee extensor fibers continuously contributes to the rapid muscle fatigue and short standing times [11, 12]. Previous work shows implanted extra-neural cuff electrodes with multiple independent contacts can selectively activate independent yet synergistic populations of motor units [2, 13,14,15]. This selectivity enables a novel technique for prolonging paralyzed muscle output and extending standing durations, termed Sum of Phase-shifted Sinusoid (SOPS) stimulation [16]. SOPS stimulation modulates the pulse width (PW) delivered through each contact such that each independently activated motor unit pool (MUP) produces a sinusoidal joint moment. When these PW patterns are phase-shifted from each other and delivered through multiple contacts simultaneously, the resulting total joint moment is constant with a value greater than the peak moment from any MUP individually (Fig. 1). SOPS stimulation therefore reduces the duty cycle of each MUP by allowing brief periods of rest while maintaining a higher overall net moment.
More at link.
Standing after upper motor neuron injury can be achieved with neural stimulation that activates the paralyzed musculature of the lower extremities [2, 3]. However, due to the rapid muscle fatigue commonly induced by extracellular stimulation [4, 5] and exacerbated by physiological changes after paralysis [6], standing times with current systems are limited and highly variable. In our laboratory, the median standing time for participants with SCI is three minutes [3], and similarly short durations have been reported by others despite various interventions for improvement [7,8,9,10]. These systems are therefore mainly beneficial for short duration tasks, such as transfers into and out of a wheelchair. Extending standing times would enable users of neuroprostheses to obtain greater physiological, functional, and social benefits from these systems.
Conventional approaches deliver non-varying stimulus current waveforms through multiple knee extensor-activating electrode contacts to ensure the joint remains locked and stable during standing. However, simultaneously activating many knee extensor fibers continuously contributes to the rapid muscle fatigue and short standing times [11, 12]. Previous work shows implanted extra-neural cuff electrodes with multiple independent contacts can selectively activate independent yet synergistic populations of motor units [2, 13,14,15]. This selectivity enables a novel technique for prolonging paralyzed muscle output and extending standing durations, termed Sum of Phase-shifted Sinusoid (SOPS) stimulation [16]. SOPS stimulation modulates the pulse width (PW) delivered through each contact such that each independently activated motor unit pool (MUP) produces a sinusoidal joint moment. When these PW patterns are phase-shifted from each other and delivered through multiple contacts simultaneously, the resulting total joint moment is constant with a value greater than the peak moment from any MUP individually (Fig. 1). SOPS stimulation therefore reduces the duty cycle of each MUP by allowing brief periods of rest while maintaining a higher overall net moment.
More at link.
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