Feasibility of closed-loop controller for righting seated posture after spinal cord injury

Abstract

Abstract-Spinal cord injury (SCI) can compromise the ability to maintain an erect seated posture. This study examined the feasibility of a sensor-based threshold controller to automatically modulate stimulation to paralyzed hip and trunk extensor muscles to restore upright sitting from forward leaning postures. Forward trunk tilt was estimated from the anterior-posterior component of gravitational acceleration sensed by a sternum-mounted wireless accelerometer. Stimulation increased if trunk tilt exceeded a specified flexion threshold and ceased once upright sitting was resumed. The controller was verified experimentally in five volunteers with SCI and successfully returned all subjects to upright postures from forward leaning positions. Upper-limb effort exerted while returning to erect posture was significantly reduced (to 7.4% +/-3.7% of body mass) pooled across all volunteers while using the controller compared with using continuous and no stimulation (p < 0.03). Controller response times were consistent among subjects when applied while sitting with (0.30 +/-0.05 s) or without (0.34 +/-0.11 s) a backrest. The controller enabled volunteers to lean farther forward (59.7° +/-16.4°) in wheelchairs without upper-limb effort than with no stimulation. Clinical utility of the system for facilitating reach or preventing falls remains to be determined in future studies.

Detecting destabilizing wheelchair conditions for maintaining seated posture

“…Neural stimulation can improve skeletal alignment, alter trunk position, enable bimanual reach and expand seated work volume, and restore erect upright sitting from a fully forward flexed position [20]. Electrically activating the paralyzed core hip and trunk muscles can stabilize seated posture and improve manual wheelchair efficiency [21] and prevent forward falls in response to applied disturbances [22,23]. Results of this study indicate that potentially destabilizing events can be detected from a relatively small number of sensors with relatively simple classification algorithms.…”

Functional Electrical Stimulation and Spinal Cord Injury

“…Moreover, they resulted in tools for evaluating more sophisticated control systems that might allow users to set their own task-dependent postures, and maintain balance during internal or external perturbations. Recent studies have established the feasibility of a self-righting control system that works on the dynamic movement of the trunk to automatically return to an erect posture from forward-flexed positions by monitoring trunk tilt and modulating stimulation to the trunk and hip extensors appropriately (Figure 7) 62 . In this study, five individuals with SCI volunteered to test a simple threshold-based set-point controller.…”

Towards transfers in paraplegia assisted by electrical stimulation and inertial system

“…This large number of transfers also contributes to the development or perpetuation of secondary upper limbs musculoskeletal impairments over time and it is known that after SCI, individuals have great risks of pain and injury in the upper limb due to joint overloads during activities of daily living [11], [1], [2]. Functional electrical stimulation (FES) can be used as a potential technological resource to assist these people during transfers [8], [10], [6], [5]. However, how the user activates the stimulation poses a problem.…”