Ventilatory efficiency and its clinical and prognostic value in adults with cystic fibrosis

Abstract

Cystic fibrosis, due to the absence or abnormal function of the cystic fibrosis transmembrane conductance regulator, is the most common life-limiting autosomal recessive genetic disorder among the Caucasian population. The lungs are particularly affected due to thick and tenacious mucus causing parenchymal anomalies ranging from bronchiectasis, progressive airflow limitation, respiratory infections, lung destruction and ultimately respiratory failure. Despite the remarkable advances in treatment that have greatly improved survival, most patients experience progressive exercise curtailment, with the consequence that a growing number of patients with cystic fibrosis will be referred for exercise-based evaluations in the forthcoming years. Cardiopulmonary exercise testing, in particular, is a useful tool to assess the mechanisms of exercise intolerance in individual patients that may have treatment and prognostic implications. In this review, we will focus on ventilatory efficiency and its clinical and prognostic value in adults with cystic fibrosis.

FIGURE 1

Representative cases of ventilatory inefficiency profiles in patients with cystic fibrosis with normal (a and b), mildly impaired (c and d) and moderately impaired (e and f) lung function. Each data point is the arithmetic mean of breath-to-breath values recorded over a 15 s period. V′_E: minute ventilation; V′_CO2: carbon dioxide output. Δ=nadir – slope difference. Reproduced from Di Paolo et al. [20], with permission.

FIGURE 2

Comparison of V′_E/V′_CO2 nadir (a), slope (c) and intercept (e) in patients with cystic fibrosis according to the severity of impairment to lung function and matched HC. Patients were divided into groups according to pulmonary function test results. G1: normal lung function: FEV₁/FVC≥0.7, FEV₁ ≥80% pred, and FVC ≥80% pred; G2: mild impairment: not satisfying criteria for G1 and FEV₁ ≥70% pred; G3: moderate impairment: not satisfying criteria for G1 and 40% ≤FEV₁<70% pred. Relative frequencies of nadir (b), slope (d), and intercept (f) above the upper limit of normality (ULN) estimated from the 95th percentile of HC distribution. ULN=28.5, 29.5, and 5.3 L·min⁻¹ for nadir, slope, and intercept, respectively. p-values intended for comparisons between all subgroups of participants. *: p<0.05 versus HC, using a post hoc test. CF: cystic fibrosis; FEV₁: forced expiratory volume in 1 s; FVC: forced vital capacity; HC: healthy controls; V′_CO2: carbon dioxide output; V′_E: minute ventilation. Reproduced from Di Paolo et al. [20], with permission.