Effect of the Leg Volume Change on the Performance of an Active Compression Brace Based on Shape Memory Alloys

Evaluating the efficacy of an active compression brace on orthostatic cardiovascular responses

Orthostatic intolerance, one of the principle causes of syncope, can occur secondary to concomitant venous pooling and enhanced capillary filtration. We aimed to evaluate a prototype portable calf active compression brace (ACB) designed to improve orthostatic haemodynamic control. Fourteen healthy volunteers participated in a randomized, placebo controlled, cross-over, double-blind study. Testing consisted of head-upright tilting and walking on a treadmill conducted on two consecutive days with a pair of ACBs wrapped around both calves. The ACB was actuated on one test day, but not on the other (placebo). Wearability, comfort, and ambulatory use of the ACB were assessed using questionnaires. The average calf pressure exerted by the ACB was 46.3±2.2 mmHg and the actuation pressure was 20.7±1.7 mmHg. When considering the differences between ACB actuation and placebo during tilt after supine rest there were trends for a larger stroke volume (+5.20±2.34%, p = 0.05) and lower heart rate (-5.12±2.41%, p = 0.06) with ACB actuation, with no effect on systolic arterial pressure (+4.86±3.41%, p = 0.18). The decrease in stroke volume after ten minutes of tilting was positively correlated with the height:calf circumference (r = 0.464; p = 0.029; n = 22; both conditions combined). The increase in heart rate after ten minutes of tilting was negatively correlated with the height:calf circumference (r = -0.485; p = 0.022; n = 22; both conditions combined) and was positively correlated with the average calf circumference (r = 0.539; p = 0.009; n = 22; both conditions combined). Participants reported good ACB wearability and comfort during ambulatory use. These data verify that the ACB increased stroke volume during tilting in healthy controls. Active calf compression garments may be a viable option for the management of orthostatic intolerance.

A Shape Memory Alloy-Based Compression Therapy Prototype Tested With Individuals in Seated Position

Orthostatic intolerance in patients can occur secondary to concomitant venous pooling and enhanced capillary filtration when standing upright, and is one of the principle causes of syncope or fainting. Compression therapy is commonly recommended for the management of syncope based on the assumption that it increases venous return. Technologies currently used include compression stockings, whose efficacy has, however, been challenged, and intermittent pneumatic pressure devices, which highly restrict the patients' mobility. This paper therefore investigates a novel active compression brace (ACB), which could potentially provide intermittent pressure while not restricting movements. The ACB, actuated by shape memory alloy (SMA) wires, in this work was tested with twelve healthy individuals in a seated position. The experimental observation showed that the ACB can apply a constant initial pressure to the leg similar to commercial compression stockings and also produce intermittent pressure exceeding 30 mmHg. A comparison between analytical and experimental results showed a maximum of 2.08 mmHg absolute averaged difference among all the participants. A correlation analysis showed that the normalized root-mean-square deviation (NRMSD) between the experimental and analytical results had a significant negative correlation with the estimated total calf circumference minus the calf fat cross-sectional area (CSA). A calibration formula, accounting for fat and circumference of the leg, was introduced to account for these two parameters. The comfort of the ACB was also compared to two other available compression devices using questionnaires. No participants reported discomfort in terms of pressure, skin irritation, or heat generated by the ACB.