Tidal breathing flow-volume loop analysis for clinical assessment of airway obstruction in conscious dogs

Using a mask, pneumotachograph, and X-Y recorder, tidal breathing flow-volume loops (TBFVL) were evaluated in 33 healthy dogs and in 18 dogs with acquired obstructive respiratory tract disease. The loops were evaluated for qualitative shape, tidal volume (VT), respiratory rate, peak and midtidal inspiratory flow (PIF and IF50, respectively), peak and midtidal expiratory flow (PEF and EF50, respectively), inspiratory and expiratory flow at end expiratory volume plus 25% VT (IF25 and EF25, respectively), inspiratory time, and expiratory time. Indices of loop shape were developed by division of flow measurements (eg, PEF/PIF and IF50/IF25). Twenty healthy dogs had the same TBFVL (type 1). Typically, PEF occurred at the beginning of expiration, and PIF occurred toward the end of inspiration. Three other TBFVL types were identified in the remaining dogs. Mean coefficients of variation for TBFVL indices ranged from 7% to 18%. Dogs with a fixed-type upper airway obstruction (pharyngeal or laryngeal mass, n = 7) had TBFVL abnormalities, indicating inspiratory and expiratory phase flattening. Concavity or late expiratory phase flattening was detected in TBFVL from dogs with chronic bronchitis/tracheal collapse (n = 11). The TBFVL were easily evaluated in conscious dogs and were useful in the functional assessment of airway obstruction.