# Severity-Dependent Peripheral Circulatory Responses to Neuroprosthetic Functional Electrical Stimulation in Chronic Stroke: A Four-Week Time Course Study

## TL;DR

This study shows that neuroprosthetic FES can improve blood flow in stroke patients, with effects appearing faster in those with milder symptoms.

## Contribution

The study introduces severity-dependent timelines for circulatory improvements using NP-FES in chronic stroke rehabilitation.

## Key findings

- NP-FES significantly increased blood flow in severe stroke patients after four weeks.
- Mild stroke patients showed circulatory improvements as early as two weeks with sensory stimulation.
- Subjective improvements in limb awareness and reduced cold sensation were reported by participants.

## Abstract

Background and objective

Chronic hemiplegia after stroke often results in disuse of the paretic limb, impaired peripheral circulation, and cold sensation. While functional electrical stimulation (FES) has been studied for motor recovery, its circulatory effects remain less explored. Neuroprosthetic FES (NP-FES), which delivers stimulation synchronized with voluntary electromyography (EMG) activity, may provide additional vascular benefits. This feasibility study aimed to evaluate whether NP-FES can induce observable changes in peripheral circulation in a day rehabilitation setting and whether response timelines differ between severe and mild hemiplegia.

Methods

Sixteen chronic stroke patients (eight severe, Brunnstrom ≤2; 8 mild, ≥5) participated in a randomized crossover trial. Each participant underwent four weeks of NP-FES and four weeks of sensory stimulation, separated by a two-week washout. Estimated blood flow (Q) was modeled from venous vessel width (VVW), skin surface temperature (Skin_Temp), and estimated hemoglobin (Hb) value. Assessments were performed pre-, post-, and 3 minutes post-stimulation at baseline, week 2, and week 4. Analyses included paired t-tests with Bonferroni correction and Bayes factors.

Results

No carryover effects were observed. In the severe group, NP-FES significantly increased Q at week 4, accompanied by an increased contribution of venous vessel width. In the mild group, sensory stimulation produced significant improvements as early as week 2. Subjective improvements, including enhanced limb awareness, initiation of use, and, in some cases, reduced cold sensation, were reported by 50% of patients with severe cases and 75% of mild cases.

Conclusions

Peripheral circulatory responses to NP-FES can be feasibly detected in clinical rehabilitation practice. The distinct timelines observed-four weeks for severe cases and two weeks for mild cases-suggest severity-specific expectations for circulation-based outcomes. These findings highlight feasibility rather than definitive efficacy and provide direction for future randomized controlled trials.