The long term goal of this project is to develop a monitor for acute pulmonary edema that is clinically useful. Electrical Impedance Imaging is a technology for making images of the interior of the body from measurements made at its surface. Small electric currents are passed through the body using electrodes attached to the skin; the resulting voltages are then measured and used by mathematical algorithms to reconstruct the values of the electrical conductivity and permittivity of the underlying structures. Because different tissues have different conductivity and permittivity, the resulting images show different anatomical structures. Further, the electrical properties of some organs, most notably the lung, change with their functional state. This offers the possibility of monitoring functions such as pulmonary edema. Present diagnostic techniques for pulmonary edema are relatively nonspecific, insensitive, and in the case of chest radiography, available only episodically and with attendant risk of ionizing radiation. Impedance imaging offers the potential to provide a continuous risk-free monitor for edema formation with regional specificity and high sensitivity. It is also possible that impedance imaging of tissue permittivity along with conductivity may provide the ability to differentiate between interstitial and alveolar edema. The investigators have developed an impedance imaging system, ACT III, which has sufficient speed and accuracy and a large enough number of electrodes to support a definitive clinical investigation of this potential application. The investigators need to determine the appropriate data to collect. Added practical concerns involve the appropriate shape, size and placement of the electrodes and their interconnection with the electronics. The ACT III electronics need to be repackaged and made more compact and reliable for clinical use. By providing a real-time bedside image of the impedance characteristics the thorax of patients who develop pulmonary edema, the investigators expect to provide a sensitive, reliable diagnostic instrument having higher sensitivity than present techniques and useful levels of regional specificity. Such an instrument is expected to have widespread clinical use in the critical care environment.