Spinal cord injury (SCI) can result in paralysis of the core trunk and hip musculature which compromises the ability to stabilize the torso while reaching, resist disturbances to sitting balance, and efficiently propel a manual wheelchair. Constant stimulation of the trunk and hip extensor muscles can positively alter seated posture, extend bimanual reach, restore erect sitting, and improve wheelchair propulsion mechanics at slow speeds and on level surfaces. However, continuously activating the trunk and hip extensors is unresponsive to the dynamically changing demands of many activities of daily living and does not contribute to attaining forward leaning postures or resisting rearward directed disturbances. First-generation systems also require users to intentionally select a discrete pattern of stimulation for each desired function from a fixed menu of pre-programmed options. The purpose of this study is to expand the functional impact of neuroprostheses for seated posture and balance by a) incorporating the abdominal and hip flexor muscles to enhance trunk stiffness through co-contraction with the extensors, b) synchronizing stimulation with the stroke cycle to improve wheelchair propulsion efficiency, c) providing automatic righting actions to maintain upright posture, prevent falls and extend forward reach, and d) integrating these approaches into an advanced sensor-driven trunk control system with currently available implantable devices in preparation for transitioning to new technologies suitable for clinical dissemination. The implanted EMG telemetry and expanded channel count of our second-generation implanted stimulator-telemeter (IST) will be utilized to implement advanced neuroprostheses for seated function. Two channels of EMG data will detect transitions between contact and return phases of propulsion and switch between appropriate stimulus patterns without conscious effort by the user. Performance of continuous co-activation of the hip/trunk flexor and extensor muscles will be compared to phasic activation of the muscles in terms of propulsion mechanics, efficiency, and subjective perception of effort on level and inclined surfaces and at various speeds. Control systems based on an inexpensive commercially available wireless 3D accelerometer will be implemented to detect impending forward or lateral falls and appropriately modulate stimulation to restore upright posture and sitting balance. Efficacy will be evaluated in terms of forward reach, rejection of disturbances, independence and safety of transfers, and both patterns of usage and fear of falling in the home and community environments. Complementary information from upper body EMG and trunk accelerations will be combined into a single control system to automatically regulate stimulation for self-righting and propulsion over various surfaces and speeds without intentional intervention by the user. Ability to discriminate between dynamic activities such as starts, stops, bumpy or inclined terrain and obstacle collisions will be determined. Usage patterns and measures of independence in the home and community will document the effects of the comprehensive control system. This translational project will establish the feasibility of a new intervention fr maximizing seated stability, facilitating personal mobility and enhancing the safety and functional independence of veterans with SCI, and in so doing define the most effective implementation for future clinical trials and widespread distribution throughout the VA healthcare system.
Spinal cord injury (SCI) significantly restricts access to life opportunities and compromises the ability to work, engage in social or leisure activities, and assume an independent and productive lifestyle. Activating the paralyzed hip and trunk muscles can promote healthy skeletal alignment, restore and maintain erect sitting postures, extend bimanual reach and the ability manipulate objects, prevent falls, improve the efficiency of manual wheelchair propulsion and facilitate transfers and other activities of daily living. This project is important because it specifies a comprehensive control system for restoring sitting posture and balance that can improve seated function by stiffening the trunk in task-dependent manners without conscious effort by the user. It is directly applicable to the health and well-being of disabled veterans who are over-represented in the SCI population.
