Assessing Upper Extremity Function in Chronic Stroke Survivors Through Acute Intermittent Hypoxia

The KAIST Upper Limb Synergy Investigation System (KULSIS) will be utilized. KULSIS was developed in collaboration with Neuro-

Figure 1: Design of the KULSIS Rehabilitation Engineering Lab at Korea Advanced Institute of Science and Technology, South Korea (Figure 1). It comprises a modular hand and wrist attachment, which connects to a linear actuator. To construct the linear actuator, ball-screw type linear motion module (RS-075N-Z05PR, Robostar, South Korea) was combined with a 100 W AC servo motor (SGM7J-01AFD2C, Yaskawa, Japan). The linear actuator has stroke range of 400 mm, which is ample for adjusting the position of modular hand or wrist attachment to the participant's upper arm before the outcome assessment. Once adjusted, the power of linear actuator will be turned off to fix the position.

A six degrees of freedom (DOF) Force/Torque sensor (Series Delta, ATI-Inc. Apex, NC, USA) is positioned between the module and the linear actuator to measure the force and torque applie

Stretch reflex thresholds will be assessed using a custom-designed tendon tapper system (Figure 2.A) based on a Linmot® linear motor (Linmot S.A., Spreitenbach, Switzerland). This system includes a stator and slider with integrated position sensing via a Hall effect sensor, ensuring precise control of tendon indentations and taps. The motor is mounted on a micrometer-driven positioner (Velmex, Bloomfield, NY, USA) for reliable placement of the tapper on the biceps brachii tendon. A multiaxial load cell (Series Nano17, ATI Industrial Automation, Apex, NC, USA) is attached at the tapping end to record applied forces and the resultant reflex responses. Additionally, the tendon tapper integrates a wireless ultrasound device(Figure 2.B) at its tip to provide real-time transverse imaging of the tissue composition surrounding the distal biceps tendon. The ultrasound device features an image resolution of 384 pixels (width) by 400-600 pixels (depth), corresponding to a physical size of 38.4 m

Surface EMG signals will be recorded using two systems to capture muscle activity during isometric contractions. The Bagnoli-8 EMG system (Delsys Inc, Boston, MA, USA), equipped with standard wired bipolar surface EMG electrodes, will provide localized muscle activity measurements. Additionally, high-density surface EMG (HDsEMG) recordings will be conducted using a 128-channel Refa system (TMSi; Oldenzaal, NL) with an 8×8 electrode grid (8.5 mm inter-electrode distance) to map spatially distributed muscle activity with high resolution (Figure 3). These complementary systems will allow a comprehensive assessment of muscle activation patterns during the study.

Standard bedside monitoring- a 2-lead tracing to identify dysrhythmias. EKG to be performed throughout hypoxia administration. 12 lead ECG to be performed at visit 1 at resting state with no other ongoing activities

A simple yes/no subjective checklist will be asked and repeated to the subject. Specifically: Chest pain, Shortness of breath, Light headedness, neck pain, dizziness, arm pain, sweaty, sensory changes, increased weakness