Electrical impedance tomography can monitor dynamic hyperinflation in dogs

Abstract

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 ml for EIT; 35 ml for Pao; and 54 ml for Pes. Subsequently, lung inflation due to applied positive end-expiratory pressure was measured by EIT (ΔV(EIT)) and Pao (ΔV(Pao)) under both inflation and deflation conditions. Whereas ΔV(Pao) was equal under both conditions, ΔV(EIT) was 28 ml greater during deflation than inflation, indicating that EIT is sensitive to lung volume history. The average inflation ΔV(EIT) was 67.7 ± 78 ml greater than ΔV(Pao), for an average volume increase of 418 ml. Lung inflation due to external expiratory resistance was measured during ventilation by EIT (ΔV(EIT,vent)) and Pes (ΔV(Pes,vent)) and at occlusion by EIT (ΔV(EIT,occl)), Pes, and Pao. The average differences between EIT estimates and ΔV(EIT,oocl) were 5.8 ± 44 ml for ΔV(EIT,vent) and 49.5 ± 34 ml for ΔV(EIT,occl). The average volume increase for all dogs was 442.2 ml. 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.