Monitoring changes in lung air and liquid volumes with electrical impedance tomography

Abstract

Electrical impedance tomography (EIT) uses electrical measurements at electrodes placed around the thorax to image changes in the conductivity distribution within the thorax. This technique is well suited to studying pulmonary function because the movement of air, blood, and extravascular fluid induces significant conductivity changes within the thorax. We conducted three experimental protocols in a total of 19 dogs to assess the accuracy with which EIT can quantify changes in the volumes of both gas and fluid in the lungs. In the first protocol, lung volume 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 ml. In the second protocol, EIT measurements were made at end expiration and end inspiration during regular ventilation with tidal volume ranging from 100 to 1,000 ml. The average error in the EIT estimates of tidal volume was 90 +/- 43 ml. In the third protocol, lung liquid volume was measured by instilling 5% albumin solution into a lung lobe in increments 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 into 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.

Effect of High-Flow Nasal Cannula and Body Position on End-Expiratory Lung Volume: A Cohort Study Using Electrical Impedance Tomography

“…A good correlation has been previously demonstrated between changes in lung impedance measured by EIT and changes in lung volume, 30,[33][34][35][36][37] suggesting that the application of high-flow therapy could increase functional residual capacity. This finding was already reported in a recent study, 19 where HFNC significantly increased global EELI in a population of post-cardiac surgery patients with respiratory dysfunction.…”

Regional lung derecruitment after endotracheal suction during volume- or pressure-controlled ventilation: a study using electric impedance tomography

“…Before starting the experimental protocol ventilation induced changes in electric impedance were calibrated against known lung volumes using a super syringe [85,86]. In steps of 200 ml, 800 ml was inflated and then deflated.…”

“…The EIT device used (Papers III and IV) for continuous FRC evaluation measures impedance changes in a ~ 5 cm thick slice of the thoracic cavity. The thickness of the slice is radius dependent [86] but also electrode size dependent. Movements of the lung could result in different parts of the lung being measured during a respiratory cycle.…”

Detection of unreliable measurements in multi-sensor devices

“…The measurement system used for these experiments has 16 electrodes; for each current pattern, there are 13 electrode pairs not used for current application at which the voltage is read. Data were acquired from a previous study in which mechanically ventilated mongrel dogs were monitored with sixteen EIT electrodes spaced evenly around the shaved thorax [2].…”