Physiological Responses to Upper Limb NMES

Exploring Local Physiological Changes in the Arm During NMES Using the Firefly® Device

The primary objective of this study is to explore the application of the Firefly® device for delivering NMES to anatomically defined regions of the upper limb and to observe associated physiological changes. Specifically, the study will assess alterations in arterial and venous blood flow, as well as local muscle oxygen saturation, as potential indicators of muscle perfusion during NMES.

Study Overview

• Status: Completed
• Conditions: Healthy Adult Participants
• Intervention / Treatment: Device: Firefly NMES device

Detailed Description

Participants will undergo NMES using the Firefly® device, applied to two predefined regions of the upper limb: one targeting the anterior arm nerve bundle (a collective term referring to motor and sensory nerves within the anterior and medial compartments of the upper arm, including the musculocutaneous and adjacent (median, medial cutaneous, ulnar and radial) nerves, and the other targeting the median nerve in the proximal forearm.

Vascular responses will be assessed at two sites, the brachial artery and axillary vein, using Doppler ultrasound. For each nerve-vascular site pairing, NMES will alternate between stimulation OFF and ON conditions (10 OFF and 10 ON cycles), comprising one stimulation block of approximately 20 minutes. Each participant will complete four stimulation blocks in total.

During both ON and OFF phases, blood flow volume and haemodynamic parameters, including peak systolic velocity (PSV), end-diastolic velocity (EDV), and resistive index (RI), will be recorded. Additionally, local muscle oxygen saturation (SmO₂) will be continuously monitored using functional near-infrared spectroscopy (fNIRS) to assess tissue-level physiological changes.

The total study participation time per individual is approximately 2 hours.

• Study Type: Interventional
• Enrollment (Actual): 10
• Phase: Not Applicable

Contacts and Locations

Study Locations

• United Kingdom
  • Buckinghamshire
    • High Wycombe, Buckinghamshire, United Kingdom, HP11 1JX
      • Firstkind

Participation Criteria

Eligibility Criteria

• Ages Eligible for Study: Adult
• Accepts Healthy Volunteers: No

Description

Inclusion Criteria:

• Aged 18 to 45 years (inclusive)
• No known history of vascular or neurological conditions affecting the upper extremities
• Able to read, understand, and communicate in English to ensure informed consent and safe participation in the study

Exclusion Criteria:

• Presence of any condition that contraindicates the use of neuromuscular electrical stimulation (e.g., implanted pacemaker, epilepsy)
• Current or recent injury to the upper limbs that may interfere with stimulation or measurement
• Anatomical variations in the brachial artery or axillary vein, specifically vascular branching outside expected anatomical locations, as identified by ultrasound, which may impair accurate blood flow measurement or device placement
• Currently participating in another interventional or physiological research study or having done so within the past 30 days.
• Currently pregnant

Study Plan

How is the study designed?

Design Details

• Primary Purpose: Basic Science
• Allocation: N/A
• Interventional Model: Single Group Assignment
• Masking: None (Open Label)

Number of Arms

1

Arms and Interventions

Participant Group / Arm	Intervention / Treatment
Experimental: Single experimental arm: Firefly NMES	Device: Firefly NMES device; Firefly NMES device applied to the upper limb during a single-visit exploratory pysiological study

What is the study measuring?

Primary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Change in upper-limb blood flow volume during NMES (ON vs OFF)	Within-subject change in upper-limb blood flow volume (mL/min) measured using Doppler ultrasound during neuromuscular electrical stimulation (NMES) delivered via the Firefly device, comparing stimulation ON versus OFF conditions. Measurements will be collected across repeated stimulation cycles at predefined upper-limb stimulation zones and vascular assessment sites.	During single study visit (approximately 2 hours), across repeated stimulation ON/OFF cycles
Change in upper-limb peak systolic velocity during NMES (ON vs OFF)	Within-subject change in upper-limb peak systolic velocity (PSV; cm/s) measured using Doppler ultrasound during NMES delivered via the Firefly device, comparing stimulation ON versus OFF conditions across repeated stimulation cycles at predefined upper-limb stimulation zones and vascular assessment sites.	During a single study visit (approximately 2 hours), across repeated stimulation ON/OFF cycles.
Change in upper-limb end-diastolic velocity during NMES (ON vs OFF)	Within-subject change in upper-limb end-diastolic velocity (EDV; cm/s) measured using Doppler ultrasound during NMES delivered via the Firefly device, comparing stimulation ON versus OFF conditions across repeated stimulation cycles at predefined upper-limb stimulation zones and vascular assessment sites.	During a single study visit (approximately 2 hours), across repeated stimulation ON/OFF cycles.
Change in upper-limb resistive index during NMES (ON vs OFF)	Within-subject change in upper-limb resistive index (RI; unitless ratio) derived from Doppler ultrasound measurements during NMES delivered via the Firefly device, comparing stimulation ON versus OFF conditions across repeated stimulation cycles at predefined upper-limb stimulation zones and vascular assessment sites.	During a single study visit (approximately 2 hours), across repeated stimulation ON/OFF cycles.
Change in upper-limb muscle oxygen saturation during NMES (ON vs OFF)	Within-subject change in upper-limb muscle oxygen saturation (SmO₂; %) measured continuously using functional near-infrared spectroscopy (fNIRS) during NMES delivered via the Firefly device, comparing stimulation ON versus OFF conditions across repeated stimulation cycles at predefined upper-limb stimulation zones and assessment sites.	During a single study visit (approximately 2 hours), across repeated stimulation ON/OFF cycles.

Secondary Outcome Measures

Outcome Measure	Measure Description	Time Frame
Incidence of adverse events and device-related effects	Number and type of adverse events (AEs), serious adverse events (SAEs), adverse device effects (ADEs), serious adverse device effects (SADEs), and device deficiencies observed during study participation.	During single study visit (approximately 2 hours)

Collaborators and Investigators

• Sponsor: Kieron.Day

Study record dates

Study Major Dates

• Study Start (Actual): September 19, 2025
• Primary Completion (Actual): October 3, 2025
• Study Completion (Actual): October 3, 2025

Study Registration Dates

• First Submitted: April 10, 2026
• First Submitted That Met QC Criteria: June 3, 2026
• First Posted (Actual): June 9, 2026

Study Record Updates

• Last Update Posted (Actual): June 9, 2026
• Last Update Submitted That Met QC Criteria: June 3, 2026
• Last Verified: June 1, 2026

More Information

Terms related to this study

• Keywords: Neuromuscular Electrical Stimulation; Hemodynamics; Muscle Contraction; Blood Circulation
• Other Study ID Numbers: FFR-ARM-002 (Other Grant/Funding Number: Firstkind)

Plan for Individual participant data (IPD)

• Plan to Share Individual Participant Data (IPD)?: YES
• IPD Plan Description: Available upon request
• IPD Sharing Supporting Information Type: STUDY_PROTOCOL; ICF

Drug and device information, study documents

• Studies a U.S. FDA-regulated drug product: No
• Studies a U.S. FDA-regulated device product: No
• product manufactured in and exported from the U.S.: No