Predictive equations measuring lung and lung lobe volumes in dogs based on thoracic height and width show promise with adjustments for some breeds

Objective: To develop and assess predictive equations for calculating lung and lung lobe volumes based on thoracic CT measurements in Shiba Inus, French Bulldogs, Chihuahuas, Miniature Dachshunds, and Toy Poodles. Methods: This retrospective analysis utilized CT data acquired from April 27, 2018, through November 8, 2024, from 5 dog breeds without respiratory or circulatory diseases. Volumes of the 7 lobes and thoracic cavity were measured. The total lung volume (TLV) was defined as the sum of all lobar volumes. Lobar volume proportions, interlobar volume ratios, and TLV-to-thoracic volume ratios were analyzed across breeds. Predictive equations for TLV and lobar volumes were derived using linear regression and lobar proportions. Results: A total of 47 dogs were included. Significant between-breed differences were observed for all lobar volumes and TLV proportions of the middle, accessory, and caudal part of the left cranial lobe, whereas the TLV-to-thoracic volume ratio showed no differences among breeds. Within breeds, the volume of the entire left cranial lobe, combining cranial and caudal parts, was equivalent to the right cranial lobe in most breeds. Most breeds showed no significant differences in volume between the left and right caudal lobes or between the middle and accessory lobes. Mean error rates obtained from predictive equations were around 20% for all volumes. Conclusions: This study revealed breed differences in pulmonary lobe volumes and proportions. Clinical Relevance: The baseline data on CT-derived lobar volumes for each dog breed might provide a foundation for future research investigating changes in lobar volumes.