A preliminary investigation on the use of shape memory alloys for lower limb compression

Compression therapy is commonly prescribed for chronic venous insufficiency indication to mitigate various complications in lower extremities including pain, swelling, edema, skin changes, and ulcerations. Compression therapy also manages orthostatic intolerance, one of the principal causes of syncope, based on the assumption of increasing venous return. Compression achieved with stockings is effective only during the supine and walking conditions, while intermittent pneumatic pressure pumps are usually limited to non-ambulatory use. The purpose of this study was to conduct a preliminary investigation on the use of shape memory alloys (SMA) to produce intermittent compression on the human calf. Thus, the research contributes towards a better understanding of utilizing SMAs in the potential development of an active compression device for the lower extremity. An active compression brace proof-of-concept prototype (ACBPP), actuated by SMA wires, was developed along with an analytical model. The use of SMA wires as actuators was investigated by conducting tests applying varying compression on a calf model. After modifying the analytical model, the effect of calf deformation on the performance of the ACBPP due to external pressure was experimentally and analytically investigated when wrapped around a compressible and incompressible calf. Through the development of a 2D finite element model of the leg, the effects of applied external pressure on the internal tissue was examined. The performance, wearability, comfort, potential haemodynamic benefits, and ambulatory use of SMAs in the ACBPP were explored through tests conducted on healthy individuals. First, results of a study on twelve healthy individuals in a seated position showed that the SMA-based ACBPP could apply a constant initial pressure to the leg, similar to commercial compression stockings, and produce intermittent pressures exceeding 30 mmHg. Second, with fourteen healthy volunteers in a randomized, placebo controlled, cross-over, double-blind study, the haemodynamic effects of using the ACBPP on human calves were preliminarily investigated during ambulatory use. This proof-of-concept investigation showed that SMAs could potentially be used to increase stroke volume during tilting in healthy controls. Participants feedback showed good ratings for the ACBPP’s wearability and comfort in both studies.