Hypercapnia and lung function parameters in chronic obstructive pulmonary disease

Abstract

Background: In advanced chronic obstructive pulmonary disease (COPD), hypercapnia may occur due to severe bronchial obstruction with lung hyperinflation. Non-invasive ventilation (NIV) provides the standard of care intended to achieve physiological PCO₂ levels, thereby reducing overall mortality. The present study aimed to evaluate pulmonary function parameters derived from spirometry (forced vital capacity [FVC], forced expiratory volume in 1 s [FEV1]), body plethysmography (residual volume [RV], total lung capacity [TLC]), and lung diffusion capacity for carbon monoxide (single-breath method [DCO-SB], alveolar-volume corrected values [DCO-VA]) as predictors of chronic hypercapnia in patients with advanced COPD.

Methods: This monocentric, retrospective observational study included 423 COPD patients. Receiver operating characteristic (ROC) curve analysis and cross-validation were used to assess lung function parameters' diagnostic accuracy for predicting chronic hypercapnia, with the resulting performance expressed as area under the ROC curve (AUROC). We performed univariable and multivariable binary logistic regression analysis to determine if these parameters were independently associated with chronic hypercapnia, with probabilities reported as odds ratios [OR] with 95% confidence intervals [95%CI].

Results: FVC% (AUROC 0.77 [95%CI 0.72-0.81], P < 0.01) and FEV1% (AURIC 0.75 [95%CI 0.70-0.79], P < 0.01) exhibited reasonable accuracy in the prediction of chronic hypercapnia, whereas lung diffusion capacity performed poorly (AUROC 0.64 [95%CI 0.58-0.71] for DCO-SB%, P < 0.01). FVC% (OR 0.95 [95%CI 0.93-0.97], P < 0.01) and FEV1% (OR 0.97 [95%CI 0.94-0.99], P = 0.029) were the only parameters associated independently with chronic hypercapnia in logistic regression analysis. FVC and FEV1 thresholds that best separated hypercapnic from normocapnic subjects reached 56% and 33% of predicted values.

Conclusions: Routinely collected pulmonary function parameters, particularly FVC% and FEV1%, may predict chronic hypercapnia during COPD progression.

Keywords: COPD; Hypercapnia; Lung function parameters; Pulmonary function tests.

Fig. 1

Patient flow diagram. Abbreviations: COPD chronic obstructive pulmonary disease, ECOPD exacerbations of COPD, NIV non-invasive ventilation, FEV1%FVC Tiffeneau index

Fig. 2

Comparison of ROC curves for selected pulmonary function parameters analyzed to predict chronic hypercapnia. Abbreviations: FVC forced vital capacity, FEV1 forced expiratory volume in 1 s, RV residual volume, TLC total lung capacity, DCO-SB single-breath lung diffusion capacity for carbon monoxide, DCO-VA transfer coefficient for carbon monoxide (Krogh index)

Fig. 3

Rank correlations of selected pulmonary function parameters with spontaneous breathing PCO₂. The heat map of Spearman’s rank correlation coefficients (ρ) with the LOESS (Local Regression Smoothing) trendline. Abbreviations: ρ, Spearman’s correlation coefficient (with 95% confidence interval); FEV1, forced expiratory volume in 1 s; DCO-SB, single-breath lung diffusion capacity for carbon monoxide; DCO-VA, transfer coefficient for carbon monoxide (Krogh index)

Fig. 4

PCO₂ as a function of FVC% and FEV1%: Linear regression analysis. Abbreviations: FVC forced vital capacity, FEV1 forced expiratory volume in 1 s