Functional Predictors of Exertional Dyspnea, 6-min Walking Distance and HRCT Fibrosis Score in Idiopathic Pulmonary Fibrosis

Abstract

Background: Exertional dyspnea and exercise incapacity are the most prominent and disabling symptoms and the main contributors to health-related quality of life in patients with idiopathic pulmonary fibrosis (IPF). Objectives: There are no comprehensive studies on pulmonary function tests (PFTs), dyspnea, exercise capacity and radiographic scores in IPF. We therefore sought to investigate the functional variables that can predict dyspnea, exercise capacity and disease extent in IPF. Methods: Thirty-four patients with IPF according to the ATS/ERS criteria underwent PFTs, Medical Research Council (MRC) dyspnea scoring, 6-min walking distance (6-MWD) and radiographic evaluation of fibrosis (HRCT score). Results: The 6-MWD (% pred.) was more impaired than PFTs. Residual volume (RV) showed the best correlation with the extent of fibrosis (r = –0.67, p = 0.0001) and, together with the alveolar-arterial gradient for O₂ [ΔP(A – a)O₂], was an independent predictor of disease extent (R² = 0.44). PFTs showed significant though weak correlations with MRC score and 6-MWD. According to the regression analysis, DL_CO and the HRCT fibrosis score were independent predictors of dyspnea, though they explained only 28% of the overall variance. FEV₁ and ΔP(A – a)O₂ were independent predictors of 6-MWD (R² = 0.31). Conclusions: PFTs and lung volumes in particular are closely related to the HRCT score, a measure of the extent of IPF. The correlation of dyspnea score and 6-MWD to PFTs is limited, due to the complexity of mechanisms leading to exercise limitation in IPF. Therefore dyspnea and exercise performance are largely independent indices and should be followed together with PFTs and HRCT score in order to better assess the status and progress of IPF patients.