Evaluation of variables to describe the shape of volumetric capnography curves during bronchoconstriction in dogs

The aim of the study was to investigate changes in volumetric capnography (VC) variables during bronchoconstriction in dogs and compare it with total respiratory resistance (RL) measured with a Fleisch pneumotachograph. Six dogs were challenged with increasing concentrations of carbachol until obvious signs of bronchoconstriction were seen. All VC parameters were obtained before, directly after, 10 and 20 min after maximal bronchoconstriction. The slope of phase III (SIII) and airway and alveolar dead space parameters were significantly different from baseline directly after the challenge. The VC curve obtained a typical shape at the time of maximal bronchoconstriction and a trend to return to baseline shape was seen over time. A significant correlation was found for all aforementioned parameters with RL. We conclude that the shape of the VC curve in combination with dead space calculation can be used to verify bronchoconstriction on a breath-to-breath basis.