Trajectories and Prognostic Significance of 6-Minute Walk Test Parameters in Fibrotic Interstitial Lung Disease: A Multicenter Study

Pulmonary fibrosis: pathogenesis and therapeutic strategies

Pulmonary fibrosis (PF) is a chronic and progressive lung disease characterized by extensive alterations of cellular fate and function and excessive accumulation of extracellular matrix, leading to lung tissue scarring and impaired respiratory function. Although our understanding of its pathogenesis has increased, effective treatments remain scarce, and fibrotic progression is a major cause of mortality. Recent research has identified various etiological factors, including genetic predispositions, environmental exposures, and lifestyle factors, which contribute to the onset and progression of PF. Nonetheless, the precise mechanisms by which these factors interact to drive fibrosis are not yet fully elucidated. This review thoroughly examines the diverse etiological factors, cellular and molecular mechanisms, and key signaling pathways involved in PF, such as TGF-β, WNT/β-catenin, and PI3K/Akt/mTOR. It also discusses current therapeutic strategies, including antifibrotic agents like pirfenidone and nintedanib, and explores emerging treatments targeting fibrosis and cellular senescence. Emphasizing the need for omni-target approaches to overcome the limitations of current therapies, this review integrates recent findings to enhance our understanding of PF and contribute to the development of more effective prevention and management strategies, ultimately improving patient outcomes.

Use of 6-minute walk distance to predict lung transplant-free survival in fibrosing non-IPF interstitial lung diseases

BACKGROUND AND OBJECTIVE

The identification of progression in patients with fibrosing non-idiopathic pulmonary fibrosis (IPF) interstitial lung diseases (ILDs) represents an ongoing clinical challenge. Lung function decline alone may have significant limitations in the detection of clinically significant progression. We hypothesized that longitudinal changes of 6-min walk distance (6MWD) from baseline, simultaneously considered with measures of lung function, may independently predict survival and identifying clinically significant progression of disease.

METHODS

Forced vital capacity (FVC), diffusing lung capacity (DLCO) and 6MWD were considered both at baseline and at 1 year in a discovery cohort (n = 105) and in a validation cohort (n = 138) from different centres. The primary endpoint was lung transplant (LTx)-free survival.

RESULTS

Average follow-up was 3 years in both cohorts. Combined incidence of deaths and LTx was 29% and 21%, respectively. No collinearity and no strong correlations were observed among FVC, DLCO and 6MWD longitudinal changes. While age, gender and BMI were not significant, 6MWD decline ≥24 m predicted LTx-free-survival significantly and independently from FVC and DLCO declines, with high sensitivity and specificity, in both the discovery and the validation cohorts. Although FVC and DLCO declines remained significant predictors of LTx-free survival, 6MWD decline was more accurate than the proposed ATS/ERS/JRS/ALAT functional criteria. Results were confirmed after stratifying patients by baseline FVC.

CONCLUSION

Longitudinal declines of 6MWD are associated with poor survival in fibrosing ILDs across a wide range of baseline severity, with high accuracy. 6MWD longitudinal decline is largely independent from lung function decline and may be integrated into the routine assessment of progression.

Impact of HRCT pattern on six-minute walk test in patients with interstitial lung disease-An observational study

Background

Forced vital capacity (FVC) and six-minute walk distance (6MWD) are robust markers in interstitial lung diseases (ILD) to assess severity and prognosis. It is unknown whether high-resolution computed tomography pattern has any independent effect on the exercise capacity in ILD. We compared six-minute walk test (6MWT) parameters between usual interstitial pneumonia (UIP) and non-UIP ILD after adjusting for FVC.

Methods

Data from a tertiary care ILD clinic were retrospectively analysed. Based on HRCT, patients were classified as UIP and non-UIP. 6MWT parameters and FVC were recorded for enrolled patients. 6MWD, distance-saturation product (DSP) and exertional desaturation were compared between UIP and non-UIP, using analysis of covariance (ANCOVA), with per cent predicted FVC as covariate. Patients were grouped as mild (≥70%), moderate (51%-69%) and severe (≤50%) based on FVC severity.

Results

Out of 169 patients enrolled, only patients with all three data points: spirometry, 6MWT and HRCT were included in the analysis (n = 139). UIP group comprised 56 (40.3%), while non-UIP group had 83 (59.7%) patients. More females and lesser smokers were present in non-UIP group. Mean predicted FVC% was similar between the two HRCT groups (P = 0.611) and had a statistically significant, though very weak to weak correlation with 6MWT parameters {6MWD (r = 0.138); pred 6MWD% (r = 0.170); desaturation (r = -0.227); DSP index (r = 0.166)}. Analysis of covariance showed no statistically significant difference in the 6MWT parameters between UIP and non-UIP groups for similar FVC levels.

Conclusion

For a similar level of lung function, exercise capacity was similar for patients with UIP and non-UIP pattern ILD.