Thoracic Impedance Gradient with Respect to Breathing

The transthoracic mutual-impedance responses to lung ventilation were measured for 37 normal subjects with 14 orthogonal lead systems. Spatial intravariability resulted from small errors in electrode placement on the thoracic surface. Temporal intravariability was determined by repeating the measurements for one subject on five consecutive days. Insignificant correlation coefficients were obtained between impedance sensitivity to lung ventilation and either age, height, weight, or chest-to-back distance of the subject. Intra-and intersubject variability were found to be of the same size for a given lead system. While the significant spatial intervariability can be easily correlated with local resistance changes due to lung volume shifts, the intersubject variability did not lend itself to correlation with subject somatotype variables.