Monitoring pulmonary edema in CHF patients with a hybrid bio-impedance approach

Frequent monitoring of lung fluid content has a key role in the diagnosis and treatment of CHF patients as the edema severity can rapidly deteriorate to cause acute respiratory distress. Practiced techniques are divided into invasive or non-invasive, with the former being impractical for regular monitoring due to patient discomfort but also due to arguably low accuracy. Non-invasive techniques consist of imaging modalities, which again cannot be used on a daily basis or at home due to considerations e.g. costs and radiation. The bio-impedance technique has been proposed for over four decades as an alternative to existing non-invasive techniques, as in principle, the lung fluids content has a large impact on the thoracic electrical impedance. In this chapter we provide a concise overview on the research done thus far for adopting the bio-impedance principles to the measurement of lung congestion, starting from the transthoracic measurement approach proposed in the late 1960s to the more sophisticated electrical-impedance-tomography spectroscopy employed in recent years. The limitations and advantages of the various approaches will be discussed. In the main part of the chapter, we will present a hybrid bio-impedance approach that has been extensively studied in our lab for a robust and reliable diagnosis and monitoring of CHF patients. The technical design of a monitoring system, and the mathematics incorporated in the estimation of the left and right lung impedance values will be described. The results of several clinical studies that were aimed at evaluating the hybrid system's feasibility in detection, classification, and monitoring of edemic patients will be given, and we will conclude by discussing the implications of the results on the realization of hybrid bio-impedance systems in the clinic and home environments for the treatment of CHF patients.