Applied potential tomography: a new technique for monitoring pulmonary function

An electrical impedance tomographic imaging system has been developed which can monitor changes in the resistivity of the thorax at a rate of 5 frames per second. There is a high correlation (r greater than 0.95) between changes in resistivity of the lungs and the volume of air inspired. Calibration of the system allows continuous monitoring of the level of ventilation on exercise up to a minute volume of 45 l min-1. The volumetric accuracy of the system is generally within +/- 10% of spirometric measurements. Studies of the effect of changes in posture on the calibration of the system show changes of between +9.5% and -3.8% in normal male subjects. The performance of the system compares favourably with existing techniques for the noninvasive monitoring of ventilation.