Ventilator-Assisted Inspiratory and Expiratory Breath-Hold Thoracic Computed Tomographic Scans Can Detect Dynamic and Static Airway Collapse in Dogs with Limited Agreement with Tracheobronchoscopy

SIMPLE SUMMARY: Airway collapse consists of the partial/complete narrowing of an airway with subsequent restriction to the airflow. It can occur anywhere along the trachea or bronchial tree in dogs and may be present throughout the respiratory cycle (i.e., static collapse) or it may be associated with a specific phase of respiration (e.g., expiration), hence “dynamic collapse”. In dogs, the clinical signs of an airway collapse may overlap those of other respiratory diseases. This study aimed to determine whether ventilator-assisted computed tomography (CT) with images acquired at inspiration and expiration would detect static and dynamic airway collapse in dogs with spontaneous respiratory disease and to compare the CT results with those obtained with tracheobronchoscopy, a modality which is commonly used to assess the airways in anesthetized dogs. The study found that the variation in the size of the airway was more profound for the trachea, the right mainstem bronchus and the right middle lobar bronchus in dogs with an airway collapse. Static collapse was only seen in the trachea of dogs with an airway collapse. The agreement between the CT and tracheobronchoscopy results was slight to moderate. The study shows that inspiratory and expiratory CT scans can detect static and dynamic airway collapse with it having limited agreement with the tracheobronchoscopy results. Scoring systems that are tailored to the clinical manifestations of function impairments may improve the comparisons in the future. ABSTRACT: Airway collapse (AC) in dogs includes a tracheal collapse, mainstem and lobar bronchial collapse, and bronchomalacia (i.e., segmental/subsegmental bronchial collapse). The clinical presentation of AC may overlap with non-collapsible airway disease (NCAD) or another non-lower airway respiratory disease (NLARD). This study determined whether paired inspiratory (I)/expiratory (E)-breath-hold computed tomography (I/E-BH CT) can detect a static and dynamic AC in dogs with spontaneous respiratory disease and it compared the CT-derived metrics of the AC to the tracheobronchoscopy metrics. The CT-acquired I and E diameter and cross-sectional area (CSA) for the trachea, mainstem and lobar bronchi in dogs with an AC (n = 16), NCAD (16), and NLARD (19) served for a dynamic percent of the airway narrowing (%AN) calculation. A scoring system assessed the bronchomalacia. The circularity was calculated for each airway. The results were compared to the tracheobronchoscopy collapse grading. In the dogs with an AC, the %AN was larger for the trachea, right mainstem bronchus and right middle lobar bronchus when they were compared to the dogs with NCAD and NLARD. Flattening was only identified for the trachea of the AC dogs. The agreement between the CT and tracheobronchoscopy scores was 20% from trachea to the lobar bronchi and 47% for the segmental/subsegmental bronchi. Paired I/E-BH CT can detect static and dynamic AC with limited agreement with the tracheobronchoscopy metrics. Independent scoring systems that are tailored to the clinical manifestations of functional impairments are needed.