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

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.