Heart rate and oxygen demand of powered exoskeleton-assisted walking in persons with paraplegia.

INTRODUCTION The wheelchair remains the primary option for mobility for persons with spinal cord injury (SCI) and lower-limb paralysis. However, at present, a few classes of assistive devices are commercially available to enable these people to ambulate overground. One option is hip-knee-ankle-foot orthoses, which refer to a class of purely passive mechanical devices that enable the user to ambulate overground by keeping the knee in full extension but permitting rotation at the hip. This type of orthotic device is available in various versions and styles, which include hip guidance orthoses [1-3], reciprocating gait orthoses (RGOs) [1,4-5], and advanced reciprocating gait orthoses (ARGOs) [1,6]. Although these orthotics have been available to assist in ambulation for decades, they have not been adapted for routine use because of the high energy cost required to ambulate, difficulty in standing and sitting, and the inability to climb stairs [1,6]. Other types of devices using functional electrical stimulation (FES) to ambulate overground have been investigated. These devices provide FES on specific muscle groups of the lower-limb muscles to power leg movement. Devices using FES alone have been successful in enabling users to ambulate, but their use has been limited because of rapid muscle fatigue and difficulty controlling joint movement [7]. Hybrid systems have also been explored, combining FES and a lower-limb orthotic [8-10] with decreased associated energy expenditure because of a reduction in muscle activity of the upper limb [11]. Further attempts to improve these systems have led to other variations, such as stored-energy hybrid systems, which combine FES with an orthotic brace that transfers energy from one joint movement to drive another joint [12-13], or controlled brake orthoses, which incorporate a computer-controlled brake system to lock out the joint and control joint speeds during ambulation [14]. Most of these devices remain as concepts or prototypes and have not been commercialized. Dating back to the 1970s, efforts have been reported to make more efficient devices for overground ambulation by creating a robotic-based orthotic that incorporates motorized joints to power exoskeleton frames [15-16]. During this earlier era, the computing and battery technology was too primitive for this technology to progress to clinical use, and as such, further development of this approach was abandoned. However, recent technological advances have led to the aggressive development of a new series of powered exoskeletal devices that enable gait in persons with paralysis [17-23]. These exoskeletal systems also have the ability to address some of the limitations of prior orthotic devices because they are powered and can provide coordinated and controlled joint movements rather than rigid knee and ankle fixation. One system, ReWalk (ReWalk Robotics; Marlborough, Massachusetts), has been reported to be safe and well tolerated by the users [19-20,24] and approved by the U.S. Food and Drug Administration for use at home and in the community. The ReWalk powered exoskeleton allows the user with paralysis to perform maneuvers of standing, sitting, walking, and ascending and descending stairs [25-27]. This expanded functionality addresses a few of the limitations of the nonpowered orthotic devices. To date, the energy expenditure required to use a powered exoskeleton system for overground ambulation has not been reported. As such, the aim of this study was to investigate energy expenditure and heart rate (HR) during powered exoskeletal-assisted use during sitting, standing, and walking. Oxygen uptake (V[O.sub.2]) while using the powered exoskeleton was compared with that of other reports that have investigated the use of passive gait orthotics in persons with paraplegia. METHODS Study Design A prospective, single-group observational study was conducted at the James J. Peters Department of Veterans Affairs (VA) Medical Center, Bronx, New York, after approval from the Institutional Review Board and registration with clinicaltrials. …