Association of 6-minute walk distance and maximal work capacity assessed by ergometry in patients with obstructive and restrictive lung diseases

Abstract

Background and Objective

In patients with chronic lung diseases work load for endurance training is calculated from maximal load. If this is not known, it might be predicted on the basis of 6-minute walk distance (6MWD). We addressed the reliability of such prediction.

Methods

Within a longitudinal clinical study on the efficacy of rehabilitation, baseline data including 6MWD, maximal work load (Wmax), peripheral muscle force, lung function, fat-free mass (FFM) and dyspnoea (MMRC score) of 255 men with occupational lung diseases (asthma, asbestosis, silicosis, COPD) were evaluated.

Results

6MWD (mean 502m, SD 92m) correlated (r=0.51, p<0.05) with Wmax (mean 112Watt, SD 35Watt), without systematic differences between asthma, silicosis and COPD. The asbestosis group was evaluated separately since the regression line was different. Muscle force, lung function parameters and MMRC score correlated moderately with Wmax (p<0.05 each). Including all statistically significant predictors the correlation was r=0.76 in patients with obstructive lung function impairment and r=0.61 in asbestosis patients. The residual standard deviations of predicted Wmax were 20-28 Watt, depending on the predictors used, and the 95% prediction intervals of Wmax based on the predictor 6MWD 47-65 Watt.

Conclusions

Compared to literature data we observed weaker correlations indicating that a sufficiently reliable prediction of individual Wmax by 6MWD or related measures is not possible. Despite this, the regression lines based on a large sample of subjects might be useful for the comparison of epidemiological studies.