MONITORING CHANGES IN LUNG AIR AND LIQUID VOLUMES WITH ELECTRICAL-IMPEDANCE TOMOGRAPHY

Electrical impedance tomography (EIT) uses electrical measurements at electrodes placed around the thorax to image changes in the conductivi ty distribution within the thorax. This technique is well suited to st udying pulmonary function because the movement of air, blood, and extr avascular fluid induces significant conductivity changes within the th orax. We conducted three experimental protocols in a total of 19 dogs to assess the accuracy with which EIT can quantify changes in the volu mes of both gas and fluid in the lungs. In the first protocol, lung vo lume increments from 50 to 1,000 ml were applied with a large syringe. EIT measured these volume changes with an average error of 27 +/- 6 m l. In the second protocol, EIT measurements were made at end expiratio n and end inspiration during regular ventilation with tidal volume ran ging from 100 to 1,000 ml. The average error in the EIT estimates of t idal volume was 90 +/- 43 ml. In the third protocol, lung liquid volum e was measured by instilling 5% albumin solution into a lung lobe in i ncrements ranging from 10 to 100 ml. EIT measured these volume changes with an average error of 10 +/- 10 ml and was also able to detect int o which lobe the fluid had been instilled. These results indicate that EIT can noninvasively measure changes in the volumes of both gas and fluid in the lungs with clinically useful accuracy.