Effects of 60 Min Electrostimulation With the EXOPULSE Mollii Suit on Objective Signs of Spasticity

Abstract

Background: The EXOPULSE Mollii method is an innovative full-body suit approach for non-invasive electrical stimulation, primarily designed to reduce disabling spasticity and improve motor function through the mechanism of reciprocal inhibition. This study aimed to evaluate the effectiveness of one session of stimulation with the EXOPULSE Mollii suit at different stimulation frequencies on objective signs of spasticity and clinical measures, and the subjective perceptions of the intervention. Methods: Twenty patients in the chronic phase after stroke were enrolled in a cross-over, double-blind controlled study. Electrical stimulation delivered through EXOPULSE Mollii was applied for 60 min at two active frequencies (20 and 30 Hz) and in OFF-settings (placebo) in a randomized order, every second day. Spasticity was assessed with controlled-velocity passive muscle stretches using the NeuroFlexor hand and foot modules. Surface electromyography (EMG) for characterizing flexor carpi radialis, medial gastrocnemius, and soleus muscles activation, Modified Ashworth Scale and range of motion were used as complementary tests. Finally, a questionnaire was used to assess the participants' perceptions of using the EXOPULSE Mollii suit. Results: At group level, analyses showed no significant effect of stimulation at any frequency on NeuroFlexor neural component (NC) and EMG amplitude in the upper or lower extremities (p > 0.35). Nevertheless, the effect was highly variable at the individual level, with eight patients exhibiting reduced NC (>1 N) in the upper extremity after stimulation at 30 Hz, 5 at 20 Hz and 3 in OFF settings. All these patients presented severe spasticity at baseline, i.e., NC > 8 N. Modified Ashworth ratings of spasticity and range of motion did not change significantly after stimulation at any frequency. Finally, 75% of participants reported an overall feeling of well-being during stimulation, with 25% patients describing a muscle-relaxing effect on the affected hand and/or foot at both 20 and 30 Hz. Conclusions: The 60 min of electrical stimulation with EXOPULSE Mollii suit did not reduce spasticity consistently in the upper and lower extremities in the chronic phase after stroke. Findings suggest a need for further studies in patients with severe spasticity after stroke including repeated stimulation sessions. Clinical Trial Registration: https://ichgcp.net/clinical-trials-registry/NCT04076878, identifier: NCT04076878.

Keywords: electrical stimulation; medical instrument; muscle spasticity; outcome assessment; stroke.

Conflict of interest statement

The NeuroFlexor instrument has been patented (WO/2008/121067), and the PL is a shareholder in the manufacturing company Aggero MedTech AB. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Copyright © 2021 Pennati, Bergling, Carment, Borg, Lindberg and Palmcrantz.

Figures

Figure 1

The EXOPULSE Mollii suit. This figure has been reproduced with permission from EXONEURAL NETWORK AB.

Figure 2

Semi-structured questions asked to the patients during each of the three sessions of stimulation with EXOPULSE Mollii.

Figure 3

Example of NeuroFlexor force trace and electromyography signal before and after stimulation with EXOPULSE Mollii. (A) NeuroFlexor hand module resistance profile during the fast velocity movement, before and after 60 min of electrical stimulation with EXOPULSE Mollii at 30 Hz. Blue trace shows the angle of wrist movement, from 20° of palmar flexion to 30° of extension. Bright red trace shows resisting force to the passive stretch and the ticker dark red line shows resistance profile when the device ran without hand. Arrow shows the late resistance toward the end of the movement (P2 time point). Values of neural component (NC) are reported in Newton, N. (B) Electromyography (EMG) signal of the flexor carpi radialis recorded synchronized with the NeuroFlexor assessment from onset (i.e., 20° of flexion) until full extension of wrist (offset, i.e., 30°). The amplitude of EMG signal is reported in mV. After stimulation, a decreased NC was accompanied by a reduced EMG amplitude (i.e., smaller burst in EMG signal in green).

Figure 4

Changes in spasticity of the upper extremity during and after stimulation with EXOPULSE Mollii. A slight increase (p > 0.05) in (A) the NeuroFlexor neural component (in Newton, N) and in (B) the electromyography (EMG) amplitude of the flexor carpi radialis (in mV) was observed during and after stimulation with the EXOPULSE Mollii suit at different frequencies: OFF-settings = circles, 20 Hz = solid triangle and 30 Hz = square.

Figure 5

Individual changes in NeuroFlexor neural component in the upper extremity during and after stimulation with EXOPULSE Mollii, graphically presented by type of response (DeltaA−B NC). A high variability of the EXOPULSE Mollii effect on NeuroFlexor neural component (NC, in Newton, N) was observed at individual level. Three patients out of 20 presented a negative DeltaA−B NC (i.e., the difference in NC between after stimulation value and before stimulation value) in OFF-settings, six patients at 20 Hz and eight at 30 Hz. To notice, NC before electrical stimulation was >14 N for OFF-settings, >13 N for 20 Hz and >8 N for 30 Hz among these patients. Nine patients presented a positive DeltaA−B NC in OFF-settings, 11 patients at 20 Hz and seven patients at 30 Hz. DeltaA−B NC within the margin of measurement error of 1 N was considered stable.

Figure 6

Individual changes in spasticity in the upper and lower extremities after stimulation with EXOPULSE Mollii. Correlation between values of NeuroFlexor neural component (NC, in Newton, N) before electrical stimulation with the EXOPULSE Mollii suit, and DeltaA−B NC (i.e., the difference in NC between after stimulation value and before stimulation value) in (A) the upper extremity (N = 20) and (B) lower extremity (n = 10). Solid circles represent the reduction in NC beyond the margin of measurement error (i.e., 1 N).