The value of high-resolution computed tomography (HRCT) to determine exercise ventilatory inefficiency and dynamic hyperinflation in adult patients with cystic fibrosis

Abstract

Introduction: In Cystic Fibrosis (CF), exercise ventilatory inefficiency and dynamic hyperinflation (DH) cause exercise limitation and induce poor exercise tolerance. High-resolution computed tomography (HRCT) of the lung can detect pulmonary abnormalities in CF patients. We aimed to identify the determinants of exercise ventilatory inefficiency and DH using HRCT-derived metrics.

Methods: Fifty-two adult CF patients were prospectively enrolled; all participants underwent cardio-pulmonary exercise test (CPET) and HRCT. Radiological impairment was evaluated by the Brody II scoring system. Slope and intercept of the minute ventilation/CO₂ production (V'_E/V'_CO2) regression line and the ratio of inspiratory capacity/total lung capacity (IC/TLC) at rest and at peak of exercise were measured.

Results: Four groups of patients were identified based on the combination of ventilatory efficiency (Vef) or inefficiency (Vin) and the presence/absence of DH. Compared to other groups, CF adults with Vin and DH had worse functional status and higher total (T), bronchiectasis (B) and air trapping (AT) scores at HRCT. Significant correlations were found between V'_E/V'_{CO2 intercept} and V'_E/V'_{CO2 slope} (ρ - 0.455, p = 0.001) and between V'_E/V'_{CO2 intercept} and Δ inspiratory capacity (IC) (ρ - 0.334, p = 0.015). Regression analysis identified AT score (cut-off 7.9, odds ratio-OR 3.50) as the only independent predictor of Vin and T (cut-off 53.6, OR 4.98), B (cut-off 16.1, OR 4.88), airways wall thickening (AWT) (cut-off 13, OR 3.41), and mucous plugging (MP) scores (cut-off 11.7, OR 4.18) as significant predictors of DH.

Conclusion: In adult CF cohort, values of HRCT metrics are determinants of Vin (AT) and DH (T, B, AWT, MP).

Keywords: Brody II score; Cystic fibrosis; Dynamic hyperinflation; Ventilatory inefficiency.

Fig. 1

Example of HRCT metrics according to the Brody II scoring system. Abbreviations: BLD indicates bronchial lumen diameter; AOD, adjacent pulmonary artery outer diameter; BWT, bronchial wall thickening

Fig. 2

Boxplots of HRCT variables in study sample. Abbreviations: T indicates total score; B, bronchiectasis score; AWT, airways wall thickening score; MP, mucous plugging score; P, parenchyma score; AT, air trapping score

Fig. 3

Boxplots of HRCT variables according to the presence of associated ventilatory efficiency/inefficiency and/or presence or absence of dynamic hyperinflation ((top), ventilatory efficiency/inefficiency only (bottom left), and presence/absence of dynamic hyperinflation only (bottom right). Abbreviations: Vef and Vin indicates ventilator efficiency and inefficiency, respectively; DH, dynamic hyperinflation; T, total score; B, bronchiectasis score; AWT, airways wall thickening score; MP, mucous plugging score; P, parenchyma score; AT, air trapping score. ^a p value calculated between groups; ^b p < 0.05 versus patients with Vef and without DH; ^c p < 0.05 versus patients with Vin and without DH; ^d p value < 0.05 versus patients with Vef and with DH

Fig. 4

Scatterplots between V’_E/V’_{CO2 slope}, Δ IC and V’_E/V’_{CO2 intercept}. Continuous and dash lines represent fit line and 95% CI, respectively. Vertical lines in the above scatterplots represent the defined cut-off of V’_E/V’_{CO2 slope} and Δ IC (30 and − 100 L, respectively)

Fig. 5

Boxplots of V’_E/V’_{CO2 intercept} according to the presence of associated ventilatory efficiency/inefficiency and/or presence or absence of dynamic hyperinflation. Abbreviations: Vef and Vin indicates ventilator efficiency and inefficiency, respectively; DH, dynamic hyperinflation. ^a p < 0.05