Improving Mobility in Peripheral Artery Disease Using an Ankle Foot Orthosis

Peripheral artery disease (PAD) is a common cardiovascular disease manifesting from atherosclerotic blockages in the arteries of the legs. The most prevalent symptom of PAD is intermittent claudication, defined as pain or discomfort in the legs that is produced by physical activity and is relieved only through rest. PAD results in significant functional limitations such as slower walking velocity and an overall sedentary lifestyle. Prior research has documented significant deficits in gait biomechanics; specifically, an inability of the ankle plantar flexors to generate normal torque and power. Furthermore, insufficient blood flow was not found to be the only mechanism contributing to gait dysfunction in patients with PAD, but the affected muscle also demonstrates a myopathy that prevents normal leg function in these patients. Thus, treatment must consider muscular function and hemodynamics to improve function and increase activity levels. Supervised treadmill walking exercise is an effective treatment for increasing the distances patients with PAD can walk. However, there is a critical treatment gap for individuals whose disease presentations warrant a non--operative treatment plan but lack the motivation, time, access and monetary resources for supervised therapy. An ankle--foot orthosis (AFO) to offset ankle plantar flexor torque and power deficiency is a novel approach to increase the walking distances and physical activity levels in those with PAD. Made of a carbon-- composite material, AFOs are adjustable, affordable and could be prescribed and worn long--term to overcome the reduced propulsion and improve walking economy. The spring--like properties of carbon--composite AFOs allow energy storage at weight acceptance and return at the point of toe off, when the ankle plantar flexors are supposed to propel into the next step. Improvements in ankle kinetics and angular momentum have been reported by using an AFO with stroke, and other neuromuscular disorders affecting the legs. However, AFOs are typically worn for foot drop, and have never been implemented in patients with PAD to improve forward propulsion. Pilot work has shown that walking with an AFO instantly increases the initial and absolute walking distances in patients with PAD as much as pharmacotherapy for six months. An AFO addresses both the myopathy and low blood flow problems associated with claudication. Mechanical force from the AFO compensates for the insufficient propulsion force of the myopathic gastrocnemius muscles, while at the same time decreasing blood flow demand and muscular stress effects of ischemia. Thus an AFO allows patients to walk longer without pain or walk the distance needed to complete daily activities with less stress to the affected leg, and may preserve/improve the overall health of the PAD limb by lowering oxygen demands to PAD muscle and effort induced ischemia and stress.

Hypothesis: An AFO improves walking performance in patients with PAD by reducing the energy cost of walking and these improvements can be seen from the first time the patient uses the AFO. Further, an AFO intervention improves walking performance by improving the muscular function of patients' affected legs.

Specific Aim 1: Test the hypothesis that from its first use an AFO produces improvements in walking performance of patients with PAD by decreasing the required muscle contribution and energy cost of walking.

Specific Aim 2: Test the hypothesis that using an AFO for three months leads to progressive improvements in walking performance, physical activity levels and quality of life of patients with PAD and that these improvements correlate with improvements in the morphometric measurements, oxygenation levels, and muscle strength and endurance characteristics of the affected legs. A crossover design will be used, in which half of subjects will complete a three--month control period before, and half after, the AFO intervention.

Specific Aim 3: To determine the feasibility of a three month AFO intervention by examining acceptability (satisfaction, intent to continue use), demand (actual use, perceived demand), implementation (degree of use, success or failure of use, factors affecting use), and practicality (effects, ability of participants to use AFO).

If the hypothesis is correct, the study will be the first to demonstrate that a simple, accessible AFO device can rapidly improve functional status and quality of life in patients with PAD immediately by decreasing the required muscular contribution and oxygen demands to PAD muscle. Additionally, Aim #2 will evaluate the long--term effects of wearing an AFO on functional status and quality of life. Aim #3 will help the investigative team ensure it is feasible to implement the AFO in our target population. Detailed measures of mechanisms related with walking performance, muscle contribution, physical activity, quality of life and how these mechanisms change after wearing the AFO for three months will provide the evidence required to implement an AFO therapy that will improve functional status and quality of life in individuals with PAD.