A Clinical Evaluation of Thoracic Electrical Impedance

The objective of this study was to evaluate the application of electrical impedance plethysmography to thoracic hemodynamic measurements. The electrical impedance technique of computing cardiac output and detecting changes in pulmonary intravascular volume was investigated. Cardiac output, as determined by electrical impedance, was compared to cardiac output by thermal dilution on patients in the intensive care unit and cardiac catheterization laboratory. On the same patient groups, changes in pulmonary intravascular pressure were correlated against changes in thoracic baseline impedance. The study revealed that the impedance method was reliable and predictable for computing cardiac output when compared to thermal dilution. Although cardiac output by electrical impedance was slightly greater than the thermal dilution standard, changes in cardiac output as determined by these two methods were linear. The pulmonary-pressure vs. baseline-impedance comparison in this study revealed that changes in thoracic baseline impedance reflect small changes in pulmonary pressure. Alterations in pulmonary pressure due to changes in left ventricular function are consistently associated with a change in baseline impedance in the expected direction.