IMSE Publications

A small, wearable, low-weight, and low-power-consumption device for plethysmography capacitive sensing is proposed herein. The device allows carrying out real-time monitoring of leg volume changes in patients suffering from heart failure (HF) conditions. The dynamic of fluid overload in patients with acute HF serves as a prognosis marker for this type of severe disease and, consequently, these patients can benefit from a wearable monitoring system to measure their body volume evolution during and after hospitalization. Our approach is based on contactless capacitive wearable structures implemented by two different sensor realizations located in the ankle: 180°-parallel capacitor plates (two modes of operations are compared, with the patient’s body connected to ground and to the average voltage between plates) and planar-parallel capacitor plates whose overlapped surface varies with the volume of the patient’s leg. Both realizations exhibit good sensitivity to leg volume changes. The acquisition of capacitance values is performed via a simple circuit that achieves notable performance in simulated volume analysis. A preliminary pilot clinical prototype is described as well.

This work presents a procedure to calculate the edema time-evolution in HF patients from bioimpedance (BI) measurements performed in their corresponding legs. The data for diagnosis are picked-up using a wearable device specifically developed for the application in accuted heart failure patients in the context of HF-VOLUM project. The main objective of the project is the calculus of the edema or volume evaluation in legs as a consequence of liquid accumulation, basically, water, as a procedure to real time supervision of the patient health. For that, as an initial step, a calibration method is proposed to extract the extracellular volume component from bioimpedance measurements done in healthy subjects, and then, applied to unhealthy ones. In the method, intra and extra cellular resistances are calculated from fitted Cole-Cole model parameters derived from BI spectroscopy measurements, and employed for the calculus of the extracellular resistance. Results obtained in a small pilot assay, with four healthy subject and two heart failure subjects, show sensitivities in the ranges of -5.2 to -1.94 ml/Ω in leg volume for healthy people, and -122.4 to -41.47 ml/Ω in unhealthy people. Measurements taken at test point of 50 kHz frequency show comparable sensitivities. We expect to extend this pilot to a wider sample to further validation and confirmation of the proposed calibration method for wearable device here described.