Altered responses of end‐expiratory lung volume and upper airway patency to body posture in diet‐induced obese mice

OBJECTIVE: Although both obesity and body posture are important factors affecting end‐expiratory lung volume (EELV) and upper airway patency, the influence of those factors on EELV and the association between EELV and upper airway calibers are still unknown in mice. This study examined such interaction effects in obese mice to test the hypothesis that obese mice have decreased EELV accompanied by structural alterations of the upper airway. METHODS: A high‐resolution in vivo micro‐computed tomography was utilized to scan anesthetized lean and diet‐induced obese mice in the prone and supine positions, followed by quantifying lung volume and analyzing upper airway morphology. RESULTS: There was a statistically significant interaction between the effects of body weight and posture on both EELV (p = 0.0049, η (2) = 0.1041) and upper airway calibers (p = 0.0215, η (2) = 0.6304). In lean mice, EELV in the prone position was significantly larger than in the supine position (prone EELV = 193.22 ± 9.10 µl vs. supine EELV = 176.01 ± 10.91 µl; p = 0.0072), whereas obese mice did not have such an improvement in EELV in the prone position (prone EELV = 174.37 ± 20.23 µl vs. supine EELV = 183.39 ± 17.49 µl; p = 0.0981) and tended to have a smaller upper airway when EELV was low based on Spearman's correlation analysis. CONCLUSIONS: These data indicate that obesity is an important factor compromising both EELV and upper airway calibers in a posture‐dependent manner even in mice, which should be taken into consideration in future studies regarding upper airway collapse and lung mechanical properties using mice.