Relationship Between Clinical Signs and Pulmonary Function Estimated by the Single Breath Diagram for CO2 (SBD-CO2) in Horses with Chronic Obstructive Pulmonary Disease

The pulmonary health of 66 horses was assessed by a clinical examination and simple supplementary diagnostic methods. Single breath diagrams for CO 2 (SBD-CO 2 ) and derived lung function indices were used to determine pulmonary function. The clinical signs in different groups were related to the results of the lung function indices derived from the SBD-CO 2 . In horses with moderate to severe chronic obstructive pulmonary disease (COPD), a significant relationship was found between the respiratory frequency and the ratio of Bohr's dead space to the tidal volume (VD Bohr /VT), and between the physiological dead space/tidal volume ratio (VD phys /VT) and the ratio of the alveolar dead space to the alveolar tidal volume (VD alv /VT alv ), but no significant associations were found between the arterial oxygen tension (P a O 2 ) and lung function indices derived from the SBD-CO 2 . The occurrence of cough, the viscosity of tracheobronchial mucus and the amount of polynuclear neutrophils in tracheobronchial aspirates were significantly related to the expiratory tidal volume (VT), the total expired volume of CO 2 (VCO 2 ), VD Bohr /VT, VD phys /VT and VD alv /VT alv . We conclude that abnormal findings in these clinical parameters indicate a measurable ventilation and perfusion (V A /Q) mismatch which is reflected by increases in dead space, VD Bohr /VT and VD phys /VT as well as VD alv /VT alv .