Small airway lesions appear with the course of IPF and relate to the severity of pulmonary fibrosis progression

Aim Idiopathic Pulmonary Fibrosis (IPF) has been considered a disease primarily affecting the interstitium with sparing of the airways. This study was to investigate development and characteristics of small airway lesions in IPF patients. Method This study included 137 patients with IPF and 84 patients in the control group. The included IPF patients from a prospective, multicentre study. Trial registration number is NCT03666234. We grouped IPF patients by severity of disease according to fibrosis severity of CT and disease severity score. Percentage of Predicted Maximal Expiratory Flow at 25 percent(MEF25%), percentage of Predicted Maximal Expiratory Flow at 50 percent(MEF50%) and maximal Expiratory Flow between 25 and 75% of FVC(MEF25-75%) were used to evaluate the function of small airways. Airway segmentation was performed using FACT-Digital LungTM software. Differences in lung function and small airway volume, numbers and length are assessed between IPF patients with different severity and the control group. Statistical analyzes were performed using SPSS software (version 26). Results There were 114 males and 23 females in the IPF group, with an average age of 64.51 ± 10.69 years. MEF50%, MEF25% and MEF75-25% of IPF patients in different stage were lower than those in the control group. The number, length, and volume of bronchi in IPF patients were higher than those in the control group.The number of bronchi at grade 9 to 14 levels in IPF patients was higher than that in the control group. IPF patients with mild fibrosis had small airway lesions. Conclusion Small airway quantity and dysfunction exists in mild patients and persist throughout the entire disease progression.