Noninvasive measurement of intrathoracic fluids.

(A) BAND ELECTRODE ARRAY (B) CIRCUMFERENTIAL SPOT (C) LONGITUDINAL SPOT ELECTRODE ARRAY ELECTRODE ARRAY FIGUBE 1. Four terminal systems for the measurement of thoracic impedance. A. Flexible metal electrodes encircling neck and thorax. 50 kHz constant sinusoidal current (1 mA rms) was applied to electrodes 1, 4. Voltage changes reflecting thoracic impedance changes were picked up from electrodes 2, 3. B. Stainless steel “spot” electrodes (1 cm diameter) sutured to chest wall at level of sixth intercostal space. Twenty kllz constant sinusoidal current (1 mA rms) was applied to electrodes 2, 4, and impedance changes between other pairs of electrodes were recorded. C. Standard disposable ECG type electrodes were applied to thorax as shown. Twenty kHz constant sinusoidal current (1 mA rms) was applied to electrodes 1, 6, and impedance changes between electrodes 2, 3, or 4, 5 were recorded.