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Global Translational Medicine BCI-FES with static magnetic field in SCI

acquisition frequency was 1 kHz. The instructor gave a   Mus
voice command to the participant, saying, “Extend as much Mus NORM =  av av  × =100 %BB Pre (I)
as possible” to perform knee joint extension movement for  BB Pre 
approximately 5s and giving an interval of approximately
10s before repeating the activity. Concurrently with the where Mus is the rectus femoris or vastus lateralis muscle.
knee extension movement request, a digital output was The superscript NORM indicates normalization with a
percentage value of the biceps brachii muscle in the pre-
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activated using the OpenSignals program. This allowed
for the evaluation of spasticity simultaneously with the assessment period (BB ). The subscript av indicates whether
Pre
activation of the digital output in the OpenSignals the assessment is conducted before (pre) or after (post).
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program to avoid any interference in the evaluation of 2.3. Spasticity assessment
voluntary contraction in the knee extensor muscle group.
The same evaluation was performed on the bilateral biceps In all sessions, the participant underwent assessment using
brachii (dominant) muscle as a normalization criterion the modified Ashworth scale (MAS) for knee extension and
(Section 2.2.3), before the first intervention (pre) and after bilateral ankle dorsiflexion movements, evaluated through
the ninth session (post). passive mobilization of these joints, and was conducted
pre- and post-interventions (conducted intraday for both).
2.2.2. Surface electromyography processing
2.4. Interventions
Signal processing was performed using a custom routine
in the program Octave 2, and from the 5 s registered, a 2 s In the sessions following the initial evaluation (pre),
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intermediate was selected for processing. The signals were nine interventions were carried out (once a week for
filtered with a fourth-order bandpass Butterworth filter 9 consecutive weeks), with which the participant was
with a passband of 10 – 450 Hz, reducing the effect of the already familiar, having performed three sessions before
electrical network, mainly the 60, 120, 180, 240, 300, 360, the evaluation. During each session, the participant was
and 420 Hz components. The descriptors were extracted instructed to remain seated in his wheelchair while the
from the temporal and spectral domains. For temporal static magnetic field was positioned, and the electrodes
features, we selected the root mean squared (RMS) value of the sNES (Section 2.4.2) and sFES (Section 2.4.3) were
(sEMG-RMS), whereas for spectral characteristics, the fixed accordingly, as described in the subsequent sections.
median frequency (sEMG-MDF) was calculated. The learning curve of the sNES-sFES interface by the user
was evaluated by classifier accuracy and the number of
2.2.3. Signals normalization misses and hits to the sFES trigger.
The maximum voluntary isometric contraction is one 2.4.1. Static magnetic field
of the most recurrent methods for evaluating sEMG
signals. However, people with spinal cord injuries often The static magnetic field (SMF) was obtained using a
lack voluntary contractions. Unlike other neurological neodymium magnet (measuring 2 cm × 3 cm × 4 cm)
conditions, such as after a stroke, where the affected side positioned at the level of the affected spinal cord segment
can be compared with the healthy side, in SCI, this is (C7) of the participant. The value of magnetic induction to
not possible. However, in a study conducted by Fukuda determine the exact position of the SMF was approximately
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et al., sEMG signals of 24 young, physically active 0.1 T, measured using a Tunkia portable digital
female participants (20 ± 6 years old) with a body mass gaussmeter, and the intervention period with the SMF
index between 18.5 kg/m and 25 kg/m , were acquired. lasted approximately 1 h, applied during the intervention
2
2
In that study, the rectus femoris and biceps brachii were with the NES-FES interface.
analyzed using sEMG-RMS. Activities were performed 2.4.2. Surface neuroelectric signals
during (i) maximum voluntary isometric contraction and
holding dumbbells of (ii) 2, (iii) 4, (iv) 6, and (v) 8 kg, In all sessions, brain activity was recorded using gold
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respectively. Normalization was achieved by calculating electrodes (Maxxi Gold ) distributed in a 10-10 system
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the mean values along the activities of the rectus femoris pattern on the scalp with conductive paste (Carbofix ) and
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with the biceps brachii, resulting in a value of 0.54. Thus, conductive gel (Electro Ultra-gel ). The channels (unipolar)
the average value during rectus femoris muscle contraction were positioned in the Cz, C1, FCz, and CPz regions and
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is approximately 54% of that of the biceps brachii muscle. fixed with the aid of a customized EEG cap. Reference
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In this sense, the signals were normalized by the biceps channels A1 and A2 were fixed using Ag/AgCl electrodes
brachii muscle on the right side (or left when the right side on the mastoid processes of the temporal bones bilaterally.
was not accessible), as shown in Equation I: EEG data were acquired using commercial Cyton OpenBCI
Volume 3 Issue 1 (2024) 4 https://doi.org/10.36922/gtm.2285