Manubrium tracheal index versus thoracic inlet tracheal index and proximal rib3 tracheal score to radiographically assess bulldogs' tracheal diameter at 3 levels.

Objective: To evaluate the manubrium tracheal index (M-TI) at 3 levels and the correlation between M-TI and other conventional techniques.

Methods: Medical records and thoracic radiographs of healthy bulldogs were investigated. Tracheal luminal diameter (TLD) was measured at the caudal cervical, thoracic inlet, and intrathoracic tracheal regions on right lateral thoracic view. The absolute and average TLDs were standardized by the manubrium length (ML), thoracic inlet distance (Ti-D), and proximal third rib width to calculate M-TI, thoracic inlet tracheal index (Ti-TI), and proximal rib3 tracheal score (PR3-TS), respectively. Correlations between averaged tracheal diameter and each of ML, Ti-D, and proximal third rib width and between M-TI and each of Ti-TI and PR3-TS were evaluated.

Results: 100 healthy French (n = 34), English (n = 33), and American (n = 33) Bulldogs met the inclusion criteria. The narrowest tracheal diameter was identified at the thoracic inlet, which was significantly narrower than both the caudal cervical and intrathoracic tracheal regions. There was no significant difference between the caudal cervical and intrathoracic tracheal regions. Strong, positive, linear correlations were identified between TLD and each normalizing parameter (ie, ML, Ti-D, and PR3-TS). Weak-to-moderate correlations were identified between the 3 procedures (ie, M-TI, Ti-TI, and PR3-TS).

Conclusions: M-TI could be an alternative to Ti-TI and PR3-TS for monitoring TLD in bulldogs. Therefore, future screening for tracheal hypoplasia is recommended using M-TI.

Clinical relevance: Bulldogs with M-TI < 0.29 at the thoracic inlet trachea and < 0.33 at the caudal cervical and intrathoracic trachea (average M-TI < 0.32) may have tracheal hypoplasia. However, further assessments of diseased bulldogs and the repeatability of measurements are still warranted.