Short-term structural and functional changes after airway clearance therapy in cystic fibrosis

Background: Airway clearance therapy (ACT) with a high-frequency chest wall oscillation (HFCWO) vest is a common but time-consuming treatment. Its benefit to quality of life for cystic fibrosis (CF) patients is well established but has been questioned recently as new highly-effective modulator therapies begin to change the treatment landscape. ¹²⁹Xe ventilation MRI has been shown to be very sensitive to lung obstruction in mild CF disease, making it an ideal tool to identify and quantify subtle, regional changes. Methods: 20 CF patients (ages 20.7 ± 5.1 years) refrained from performing ACT before arriving for a single-day visit. Multiple-breath washout (MBW), spirometry, Xe MRI, and ultrashort echo-time (UTE) MRI were obtained twice—before and after patients performed ACT using their prescribed HFCWO vests (average 4.7 ± 0.5 h). UTE MRIs were scored for structural abnormalities, and standard functional metrics were obtained from MBW, spirometry, and Xe MRI—FEV_1,pp, LCI_2.5, and VDP_N4, respectively. Results: Spirometry and Xe MRI detected significant improvements in lung function post-ACT. 15/20 patients showed improvements from a baseline median of 92% FEV_1,pp. Similarly, 16/20 patients showed improvements in Xe MRI from a baseline median of 15.2% VDP_N4. Average individual changes were +2.6% in FEV_1,pp and -1.3% in VDP_N4, but without spatial correlations to easily-identifiable causative structural defects (e.g. mucus plugs or bronchiectasis) on UTE MRI. Conclusions: Lung function improved after a single instance of HFCWO-vest ACT and was detectable by spirometry and Xe MRI. The only common structural abnormalities were mucus plugs, which corresponded to ventilation defects, but ventilation defects were often present without visible abnormalities.