# Correlation of the Six-Minute Walk Test, Diffusing Capacity for Carbon Monoxide, and Pulmonary Function Parameters in Patients With Interstitial Lung Disease: A Cross-Sectional Study

## TL;DR

This study examines how lung function tests relate in patients with interstitial lung disease, finding a weak but significant link between the six-minute walk test and forced vital capacity.

## Contribution

The study provides new insights into the correlations between functional and physiological tests in interstitial lung disease patients.

## Key findings

- 6-MWT showed a weak but significant correlation with FVC (r=0.38; p=0.037).
- DLCO did not show significant correlations with FEV1, FVC, or total lung capacity.
- 6-MWD was significantly lower than predicted, and vital signs changed significantly after the test.

## Abstract

Background

Interstitial lung disease (ILD) encompasses a broad group of progressive lung disorders marked by inflammation and fibrosis, leading to irreversible damage. Early screening plays a pivotal role in identifying disease onset and optimizing patient outcomes. This study assessed the correlation of diffusing capacity for carbon monoxide (DLCO) with the six-minute walk test (6-MWT) and pulmonary function test (PFT) parameters. Moreover, the correlation between 6-MWT and PFT parameters was evaluated.

Methods

This cross-sectional study, involving 30 patients with high-resolution computed tomography-proven ILD, was performed over a period of 24 months (October 2022 to September 2024) in the Department of Respiratory Medicine of Government Medical College, Nagpur, in Nagpur, India. All patients underwent 6-MWT and PFT. Vital parameters were assessed before and immediately after 6-MWT, and the six-minute walk distance (6-MWD) was calculated.

Results

6-MWT had a weakly positive and significant correlation with forced vital capacity (FVC) (r=0.38; p=0.037), but not with forced expiratory volume in one second (FEV1) and DLCO (p>0.05). DLCO had a positive and non-significant correlation with total lung capacity, FEV1, and FVC, while correlation with FEV1/FVC ratio was negative and non-significant (p>0.05). Actual 6-MWD was significantly lower than the predicted value (p<0.001). Immediately after 6-MWT, there was a significant decrease in oxygen saturation, while systolic blood pressure, pulse rate, and respiratory rate increased significantly compared to baseline 6-MWT values (p<0.001), with diastolic blood pressure being comparable at both intervals (p>0.05).

Conclusion

6-MWT had a weak but significant correlation with FVC, while the correlation between other parameters was not significant. These tests highlight functional limitations and physiological derangements, thus strengthening their role in ILD management.