Statistical shape analysis of volumetric capnograms: evaluation of a new approach for the assessment of pulmonary function in horses with chronic obstructive pulmonary disease.

The shape of the volumetric capnogram is modified by airway obstruction, and the evaluation of this deformation could allow an indirect measurement of bronchial patency. The study included 35 horses; five horses without evidence of pulmonary disease (group I) and 30 horses suffering from different degrees of chronic obstructive pulmonary disease (COPD) (groups II-IV). Data of recorded CO2 and volume curves were off-line plotted and statistically analysed using regression analysis. Analyses were performed separately for fractions 25-95% (VTE25-95), 25-50% (VTE25-50) and 50-95% (VTE50-95) of expiratory tidal volume. For VTE25-95 estimates of linear and quadratic regression parameters were significantly different between groups. For VTE25-50 linear terms were significant in all clinical groups and decreased considerably from group I to group IV. Linear and quadratic terms for VTE50-95 were significant in all clinical groups and increased with the severity of COPD. The difference of total expiratory CO2 volume was significant between all groups. Statistical analysis of the volumetric capnogram is a precise method for description of shape deformities of the single breath diagram for CO2 (SBD-CO2) in horses with COPD and global models including phase II and III of the SBD-CO2 are helpful in the detection of pulmonary function impairment. However, although the model of the statistical shape analysis of the SBD-CO2 is precise, it may not necessarily be a useful test to discriminate horses with minor, moderate and severe COPD for clinical use.