Airway to Lung Volume Ratio on CT is Associated with Pulmonary Function Transition from Obstructive to Restrictive Pattern in Obesity

Background: Obesity is associated with excessive airway collapse and reduced lung volume; it is unknown whether it affects airway-lung interactions. We sought to compare the airway tree to lung volume ratio, assessed by CT, in obese individuals with and without ventilation disorders.Methods: Participants underwent inspiratory chest CT and pulmonary function. The percentage ratio of the whole airway tree to lung volume, automatically segmented via deep learning, was defined as CT airway volume percent (AWV%). Total airway count (TAC), airway wall area percent (WA%), and other CT indexes were also measured. Results: We evaluated 88 participants including adolescents(age: 14-18, n= 12) and adults (age: 19-25, n= 17; age: 26-35, n= 39; age> 35, n= 20). Obese adolescents had higher forced vital capacity (FVC) (P = 0.001) and lower AWV% (P = 0.008) than obese adults (age >35). Among obese adults, participants with restrictive disorders had larger AWV% (P < 0.001) and those with obstructive disorders showed smaller AWV% (P < 0.001) compared to participants with normal ventilation. AWV% was positively correlated with age and forced expiratory volume in 1 second (FEV1)/FVC and adversely related to FVC (P< 0.05 for all), and in multivariate models, AWV% independently predicted FEV1/FVC (R2 = 0.49, P < 0.001) and FVC (R2 = 0.60, P < 0.001).Conclusion: Transitions in lung function patterns between obese adolescents and adults are associated with airway to lung ratios. The obesity-induced disproportion between the airway tree and lung volume may adversely affect and complicate lung ventilation.