Acute pulmonary edema assessed by electrical impedance imaging

Abstract

Acute Iung injury, with decreased cardiac output, and arterid PO2 and increased pulmonary arterial pressure was produced by intravenous injection of oleic acid in dogs. During the next three hours, resistivity decreased in two regions of the chest. corresponding lo the lungs, as measured by elecuical impedance imaging. Overall resistivity in the enlire image decreased from 179 to 143 ohm-cm in 3 hours, while the peak lung resistivity decreascd from 248 to 207 ohm-cm. We conclude that impcdance imaging holds promise for clinical monitoring of acute pulmonary edema. Introduction Pulmonary edema and Adult Respiratory Discress Syndrome remain important complications following major surgery and multiple muma. Clinical diagnosis relies on physiological tests of gas exchange, including merial blood gas measurements. wilh calculation of intrapulmonary shunt, auscultation, and chest radiographs. The present study was conducted to determine if Electrical Impedance Imaging can also provide a clinically useful assessment of pulmonary edema. Electrical Impedance Imaging is a technique for forming images of the interior of the body based on electrical measurements made From electrodes applied to the skin. Known currencs are passed through the bcdy, and the voltages resulting on the electrodes are measured. A reconstruction algorithm then uses these data to solve the inverse problem and clsplay a map or image of the resistivity in the region surrounded by the electrodes. Since significant decreases in resistivity may occur in the lungs during edema formation, they might be detectabIe by Impedance Imaging. This hypothesis is an extension of an earlier study which showed decreases in overall thoracic resistivity in pulmonary edema patients [ I ] , We have studied dogs wilh pulmonary edema induced by intravenous infusion of oleic acid, a well-studied model of acule lung injury [2]. Images of the lungs showed progressive localized decreases in resistiviv throughout Ihe edema forma-