title: Transthoracic electrical impedance: artifacts associated with electrode movement.
abstract: The applicability of transthoracic impedance measurements for estimating thoracic fluid volume and tidal volume is limited by large variations associated with electrode movement, repeated application of electrodes and inter-individual differences. These sources of variation were studied with a four-electrode impedance-measuring device in anaesthetized dogs. Electrode movement artifacts affecting both the resting expiratory value of impedance (Zo) and the respiratory change of impedance (deltaZ/VT) could be largely eliminated by rigidly fixing the distances between the current-supplying and the potential-sensing electrodes. The reproducibility of Zo and deltaZ/VT was found to be affected adversely by local conductivity changes in the skin induced by repeated removal of the glued electrodes. Inter-individual variations in Zo and deltaZ/VT correlated with the thickness of thoracic subcutaneous fat (r = 0.86) and thoracic circumference (r = -0.95) respectively. Correction for these sources of inter-individual variation allowed the standard deviations of Zo and deltaZ/VT to be reduced from 18% to 7% and from 51% to 17% of their respective mean values.
mesh_terms: D000818:Animals; D004285:Dogs; D004553:Electric Conductivity; D004566:Electrodes; D008176:Lung Volume Measurements; D008722:Methods; D011654:Pulmonary Edema / Q000175:diagnosis*; D013909:Thorax / Q000502:physiology; D013990:Tidal Volume