Is an Individual Prediction of Maximal Work Rate by 6-Minute Walk Distance and Further Measurements Reliable in Male Patients with Different Lung Diseases?

Abstract

Background: In patients with chronic lung diseases, the work rate for endurance training is calculated by the maximal work rate (W_max). Because the assessment bears side effects, a prediction by easier accessible tests would be of practical use. Objective: We addressed the reliability of predicting W_max on the basis of the 6-min walk distance (6MWD) test and a set of further parameters in patients with different lung diseases. Methods: Baseline data of a longitudinal study including 6MWD, W_max, peripheral muscle force, lung function, fat-free mass and dyspnea (Modified Medical Research Council score) of 255 men with occupational lung diseases (104 asthma, 69 asbestosis, 42 silicosis, 40 chronic obstructive pulmonary disease) were evaluated. Results: 6MWD correlated with W_max (r = 0.51, p < 0.05). The product of 6MWD and body weight, in particular fat-free mass, led to an improvement in the correlation of W_max with 6MWD. Muscle force, lung function and Modified Medical Research Council score correlated moderately but significantly with W_max (p < 0.05 each). The maximum correlation gained by including 6MWD and further parameters in the prediction equations was r = 0.76 in patients with obstructive lung function impairment and r = 0.61 in asbestosis patients. The residual standard deviations of W_max predicted by the calculated equations ranged between 20 and 28 W, and the 95% prediction intervals of W_max ranged between ±47 and ±65 W. Conclusions: A reliable prediction of individual W_max by 6MWD or related measures and therefore a replacement by other tests is not possible. Nevertheless, it may be useful for the comparison of average values in epidemiological and clinical studies.