Applied potential tomography: a new technique for monitoring pulmonary function

Abstract

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>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 +or-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.