[Pulmonary water and thoracic impedance. Evaluation of a measurement technic]

We measured transthoracic electrical impedance in 17 anesthetized and mechanically ventilated dogs with a four-electrode system. A current (5 KHZ, 50 mu A) is injected and detected at axillary levels. Transthoracic impedance was 67 +/- 14 ohms (S.D.) with insignificant shifts in control animals. Pulmonary edemas were induced by saline and dextrose overloads with large but opposite variations in impedance. Fifty to hundred per cent increases in total lung water content (determined at autopsy) were induced by intravenous injection of alloxan or instillation of endotracheal saline. Significant but small decreases in impedance followed. Validity of experimental pulmonary edemas with or without blood resistivity and pulmonary blood volume changes is discussed.