Electrical impedance tomography can monitor dynamic hyperinflation in dogs

We assessed in eight dogs the accuracy with which electrical impedance tomography (EIT) can monitor changes in lung volume by comparing the changes in mean lung conductivity obtained with EIT to changes in esophageal pressure (Pes) and to airway opening pressure (Pao) measured after airway occlusion. The average volume measurement errors were determined: 26 mi for EIT; 35 mi for Pao; and 54 mi for Pes. Subsequently, lung inflation due to applied positive end-expiratory pressure was measured by EIT (Delta V-EIT) and Pao (Delta V-Pao) under both inflation and deflation conditions. Whereas Delta V-Pao was equal under both conditions, Delta V-EIT was 28 mi greater during deflation than inflation, indicating that EIT is sensitive to lung volume history. The average inflation Delta V-EIT was 67.7 +/- 78 mi greater than Delta V-Pao, for an average volume increase of 418 mi. Lung inflation due to external expiratory resistance was measured during ventilation by EIT (Delta V-EIT,V-vent) and Pes (Delta V-Pes,V-vent) and at occlusion by EIT (Delta V-EIT,V-occl), Pes, and Pao. The average differences between EIT estimates and Delta V-EIT,V-occl were 5.8 +/- 44 ml for Delta V-EIT,V-vent and 49.5 +/- 34 mi for Delta V-EIT,V-occl. The average volume increase for all dogs was 442.2 mi. These results show that EIT can provide usefully accurate estimates of changes in lung volume over an extended time period and that the technique has promise as a means of conveniently and noninvasively monitoring lung hyperinflation.