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Part 1. Computational Fluid Dynamics Using Computed Tomography to Assess Airway Resistance in English Bulldogs. Obstructive airway disease is common in brachycephalic dogs. Stenotic nares, edematous intranasal turbinates, mucosal swelling, and an elongated, thickened soft palate are sources of airflow resistance. Surgery has traditionally focused on resection of excessive nares and soft palate, without objective measures to validate efficacy. Twenty-one non-operated brachycephalic dogs were recruited for this pilot study. A 128 multi-detector computed tomography (MD-CT) scan was performed in all dogs, from rostral nares to diaphragm (SOMATOM Definition Flash; Siemens Healthcare). MD-CT examinations were performed using conscious sedation and without endotracheal intubation. Raw MD-CT data were imported into ScanIP software (Simpleware, Version 7.0) to render a three-dimensional surface mesh model by automatic segmentation using -1024 to -450 Hounsfield units to isolate the air-filled nasal passage from the nares to the caudal soft palate. Three-dimensional surface models were then imported into COMSOL Multiphysics 5.0 with MATLAB (COMSOL, Inc., Version 5.0.1.276) for computational fluid dynamic (CFD) modeling and calculation of airway resistance. The nasal passages were modeled and airway resistance calculated in all dogs. Airway resistance varied widely; mean and SD of 9,859.19 +/- 12,818.53 Pa/L/s. Airway resistance did not correlate with age (r = 0.344, P = 0.126) or weight (r = -0.058, P = 0.803). In 19/21 dogs, the rostral third of the nasal passage showed the greatest step-up of airflow resistance. The remaining 2/21 dogs, the caudal third of the nasal passage showed the greatest resistance with the greatest increase identified at the caudal portion of the soft palate.Computational fluid dynamics derived from nasal MD-CT can quantify airway resistance in dogs. This methodology may have utility for objectively studying surgical interventions in canine brachycephalic airway syndrome.Part 2. Cardiac Dimensions Measured by Multi-Detector Computed Tomography Angiography and Transthoracic Echocardiography in Normal English Bulldogs.Transthoracic echocardiography (TTE) is the primary modality for evaluating cardiac dimensions and function in dogs. In the English bulldog, TTE is challenging due to the breed’s unique thoracic conformation with dorsoventral compression and narrow intercostal spaces. Multi-detector computed tomography angiography (MD-CTA) circumvents body conformational challenges and is a gold standard for cardiac dimensions in humans. Eleven English bulldogs underwent both TTE (Vivid 7; GE Medical Systems) and sedated MD-CTA (SOMATOM Definition Flash; Siemens Healthcare) within 24hrs of the other. Standard cardiac dimensions were compared between modalities, measured twice by the same observer and separately by two other observers. Comparisons of TTE to MD-CTA dimensions were performed by Student’s t-test if normal or Wilcoxon signed-rank test if not normal; intra-observer and inter-observer variability was assessed by coefficient of variation (CV).Eight of the 25 measurements of linear cardiac dimensions were significantly different between TTE and MD-CTA (all P < 0.033). Overall intra-observer agreement was strong with average CVs of 5.34% for TTE and 2.50% for MD-CTA. Overall inter-observer agreement CVs averaged 6.5% for TTE and 8.75% MD-CTA. Differences were found between cardiac dimensions as measured by TTE and MD-CTA, indicating the two methodologies are not equivalent. Sedated MD-CTA yielded high-quality imaging with strong intra-observer and inter-observer measurement repeatability in English bulldogs, providing cross-sectional reconstructions of cardiac morphology in a breed challenging to image by TTE. |
