Reduced exercise ventilatory efficiency in adults with cystic fibrosis and normal to moderately impaired lung function

Despite being a hallmark and an independent prognostic factor in several cardiopulmonary diseases, ventilatory efficiency—i.e., minute ventilation/carbon dioxide output relationship (V E/V CO2)— has never been systematically explored in cystic fibrosis (CF). To provide a comprehensive frame of reference regarding measures of ventilatory efficiency in CF adults with normal to moderately impaired lung function and to confirm the hypothesis that V E/V CO2 is a sensitive marker of early lung disease. CF patients were divided into three groups, according to their spirometry: normal (G1), mild impairment (G2), and moderate impairment (G3) in lung function. All participants underwent incremental cardiopulmonary exercise testing on a cycle ergometer. Lowest V E/V CO2 ratio (nadir) and the slope and the intercept of the linear region of the V E/V CO2 relationship were contrasted in a two-center retrospective analysis, involving 72 CF patients and 36 healthy controls (HC). Compared with HC, CF patients had significantly higher V E/V CO2 nadir, slope, and intercept (P 0.001, P 0.001, and P 0.049, respectively). Subgroup analysis revealed significant differences in nadir (P 0.001) and slope (P 0.012) values even between HC and G1. Dynamic hyperinflation related negatively with slope (P 0.045) and positively with intercept (P 0.001), while no impact on nadir was observed. Ventilatory inefficiency is a clear feature of adults with CF, even among patients with normal spirometry. V E/V CO2 nadir seems to be the most reliable metric to describe ventilatory efficiency in CF adults. Further prospective studies are needed to clarify whether V E/V CO2 could represent a useful marker in the evaluation of early lung disease in CF.