Comparison of inhalation-to-perfusion ratio in anesthetized dogs with barrel-shaped thorax vs dogs with deep thorax

Interregional, as well as intraregional (local), distributions of the inhalation-to-perfusion ratio were analyzed in the lungs of 20 prone anesthetized healthy dogs--10 dogs with barrel-shaped thorax (Beagles) and 10 dogs with deep thorax (Greyhound-type dogs)--using 99mTc inhalation-perfusion lung scintigraphy. Dorsoventral and lateral views were analyzed. In both types of dogs, the ratio between the mean inhalation and perfusion values (interregional mismatching factor) decreased from craniad to caudad and the decrease was more sustained in the right than in the left lung. However, the total decrease was less in Greyhound-type dogs than in Beagles (cranial-to-caudal decrease of 14 and 27%, respectively, in the left lung, and 62 and 56%, respectively, in the right lung). The dorsal-to-ventral distribution of interregional mismatching factor was different in the 2 types of dogs. In Beagles, it increased from dorsal to ventral zones by about 50% of the initial dorsal zone value, whereas in Greyhound-type dogs, only a slight dorsal-to-ventral decrease was evident, with the exception of the more ventral zone. Differences in the intraregional mismatching factor (rho) indicated that the intraregional inhalation-to-perfusion inequalities were more pronounced within the caudal regions and within the ventral zones of the lungs in both types of dogs, and in the more cranial zones in the lungs of Beagles. However, the degree of intraregional mismatching was generally lower in Greyhound-type dogs. Thus, the gravitational force is not the dominating determinant of interregional or intraregional inhalation-to-perfusion ratio distributions in the lungs of anesthetized prone dogs. Its influence is modulated by other factors morphologic characteristics, such as the shape and size of the thorax, and body weight of the dog. In particular, the height of the thorax in Greyhound-type dogs could permit the gravitational force to exert a more determinant influence than it does in Beagles.