a novel stretch sensor to measure venous hemodynamics

Chronic venous insufficiency is a debilitating condition causing varicose veins and venous ulcers. The pathophysiology includes reflux and venous obstruction. The diagnosis is often made by clinical examination and confirmed by Venous Doppler studies. Plethysmography helps to quantitatively examine the reflux and diagnose the burden of deep venous pathology to better understand venous hemodynamics, which is not elicited by venous duplex examination alone. However, most of these tests are qualitative, expensive, and not easily available. In this paper, we demonstrate the potential use of a novel stretch sensor in the assessment of venous hemodynamics during different maneuvers by measuring the change in calf circumference. We designed the stretch sensor by using semiconductor strain gauges pasted onto a small metal bar to form a load cell. The elastic and Velcro material attached to the load cell form a belt. It converts the change in limb circumference to a proportional tension (force of distension) when placed around the calf muscle. We recorded the change in limb circumference from arrays of stretch sensors by using an in-house data acquisition system. We calculated the venous volume (VV), venous filling index (VFI), ejection fraction (EF) and residual venous volume (RVV) on two normal subjects and on two patients to assess venous hemodynamics. The values (VV > 60 ml, VFI < 2ml/s, EF > 60%, RVV < 35%) in normal subjects and (VV < 60 ml, VFI > 2ml/s, EF < 60%, RVV > 35%) in patients were comparable to those reported in the literature.