Ventilation efficiency to exercise in patients with cystic fibrosis

Abstract

Introduction: Exercise ventilation efficiency index in cardiopulmonary exercise testing (CPET) is elevated in patients with heart failure providing useful information on disease progression and prognosis. Few data, however, exist for ventilation efficiency index among cystic fibrosis (CF) patients.

Aims: To assess ventilation efficiency index (ΔVE/ΔVCO₂ or V'E/V'CO₂ slope) and intercept of ventilation (VE-intercept) in CF patients with mild, moderate, and severe cystic fibrosis (CF) lung disease. To assess possible correlations with ventilation inhomogeneity and structural damages as seen on high resolution computed tomography (HRCT).

Methods: CF patients with mild (FEV₁ > 80%, n = 47), moderate (60% < FEV₁ < 80%, n = 21), and severe (FEV₁ < 60%, n = 9) lung disease, mean age 14.9 years participated. Peak oxygen uptake (VO₂ peak), pulmonary ventilation at peak exercise (VE), respiratory equivalent ratios for oxygen and carbon dioxide at peak exercise (VE/VO₂ , VE/VCO₂ ), end-tidal CO₂ (PetCO₂ ), and ΔVE/ΔVCO₂ , ΔVE/ΔVO₂ in a maximal CPET along with spirometry and multiple breath washout indices were examined. HRCT scans were performed and scored using Bhalla score.

Results: Mean ΔVE/ΔVCO₂ showed no significant differences among the three groups (P = .503). Mean VE_int discriminated significantly among the different groups (p ² < 0.001). Ventilation efficiency index did not correlate either with LCI or Bhalla score. However, VE together with ΔVE/ΔVCO₂ slope could predict Bhalla score (r ² = 0.869, P = .006).

Conclusion: No significant differences were found regarding ΔVE/ΔVCO₂ slope levels between the three groups. Ventilation intercept (VE_int ) was elevated significantly as disease progresses reflecting increased dead space ventilation. CF patients retain their ventilation efficiency to exercise even as lung function deteriorates by adopting a higher respiratory rate along with increased dead space ventilation.

Keywords: cystic fibrosis; pulmonary function testing.