Authors
   Adler A. Shinozuka N. Berthiaume Y. Guardo R. Bates JH.
Institution
   Meakins-Christie Laboratories, McGill University, Montreal, Quebec,
   Canada.
Title
   Electrical impedance tomography can monitor dynamic hyperinflation in
   dogs.
Source
   Journal of Applied Physiology. 84(2):726-32, 1998 Feb.
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 (delta VEIT) and Pao (delta VPAO) under both inflation and
   deflation conditions. Whereas delta VPAO was equal under both conditions,
   delta VEIT was 28 ml greater during deflation than inflation, indicating
   that EIT is sensitive to lung volume history. The average inflation delta
   VEIT was 67.7 +/- 78 ml greater than delta VPAO, for an average volume
   increase of 418 ml. Lung inflation due to external expiratory resistance
   was measured during ventilation by EIT (delta VEIT,vent) and Pes (delta
   VPes,vent) and at occlusion by EIT (delta VEIT,occl), Pes, and Pao. The
   average differences between EIT estimates and delta VEIT,occl were 5.8 +/-
   44 ml for delta VEIT,vent and 49.5 +/- 34 ml for delta VEIT,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.