Thoracic impedance used for measuring chest wall movement in postoperative patients.

Thoracic impedance (TTI) and rib cage inductance band (IB) signals were measured in 10 patients during the first night after abdominal surgery, and compared by successive correlation of the change in each signal. Poor matching of the signals occurred, on average, for 94 min either because of movement of differences in the waveform. There were frequent episodes of transient poor correlation, generally associated with transient respiratory disturbance, predominantly airway obstruction (58%). Thoracic impedance measurements are simpler than inductance band methods for detecting rib cage movement and may be useful for large studies of respiratory abnormalities in patients after operation.