Canine awake head-out plethysmography (HOP): Characterization of external resistive loading and spontaneous laryngeal paralysis

We applied a novel head-out plethysmographic (HOP) method to study awake canine responses to external resistive loading and natural laryngeal paralysis. Measurements of inspiratory and expiratory specific airway resistance (sRawinsp, sRawexp) were obtained before and after uni- and bidirectional loading (Radd = 5 cmH2O/L/s) in large-breed dogs (n = 9).Mean sRawinsp after inspiratory, and sRawexp after expiratory loading were 31.4 and 33.3 cmH2O s, respectively. Bidirectional loads induced a significantly greater rise in both sRawinsp and sRawexp (55.1 and 61.3 cmH2O s) compared to unidirectional loading (P < 0.001). Yet, type of loading did not affect flow-volume indices. The mean Raw of dogs was 4.81 cmH2O/L/s. Expiratory loading resulted in a significant 8.8% increase in functional-residual-capacity (FRC), compared to FRCbaseline (76.7 ml/kg). Dogs (n = 5) with laryngeal paralysis demonstrated a significant increase in sRaw and Raw compared to controls without changes in FRC. In conclusion, HOP precisely characterized sRaw in response to external resistive loading. Hence, we could accurately quantify airway obstruction in awake dogs with laryngeal paralysis.