Ambulatory sensor for circumference monitoring of lower limbs

The continuous monitoring of edema in the lower limbs of the human body is presently not possible as suitable devices are not available. This paper presents the characterization and the testing of a novel ambulatory device dedicated to the monitoring of circumference variations in the lower limb. The sensor, based on an inductive loop integrated into a textile band, is connected to a miniaturized electronic system which wirelessly sends the calculated perimeter value of the leg to a smart mobile device. In-vitro tests have demonstrated that the device enables the measurement of perimeters ranging from 25 cm to 33 cm with an accuracy of 0.3 cm. This result was obtained using a circular loop, which assumes that the shape of the leg remains circular at the location where the loop is positioned. To investigate the influence of the loop shape on the sensor response, three physical models of different shapes (circular, elliptic and triangular) were tested. It was found that self-inductance values of the loop can be predicted in an acceptable way using a theoretical model for the three different shapes. Experimental tests showed that the error in the perimeter value is around 5% of the full scale when changing the geometry from circular to elliptic but can reach 11 % from circular to triangular. The application interface developed for a smartphone is presented, which will enable the ambulatory monitoring of leg edemic swelling during daily activity and facilitate its assessment by the clinician.