CFTR and cystic fibrosis: In studies conducted prior to the introduction of cystic fibrosis transmembrane conductance regulator (CFTR) modulator therapy, children with CF showed an increased ventilation and perfusion impairment compared to healthy controls (24, 47–49, 53, 54, 58, 65, 71), especially those having frequent pulmonary exacerbations (37, 49, 51).