Six-minute walk test for the evaluation of pulmonary disease severity in scleroderma patients

Pulmonary involvement is the leading cause of systemic sclerosis (SSc)-related deaths. A simple test to evaluate exercise capacity is the 6-min walk test (6MWT), and the walk distance is used as a primary outcome in clinical trials. Hemoglobin desaturation during a 6MWT is predictive of mortality in patients with primary pulmonary hypertension. Our objectives were to evaluate the walk distance and resting oxygen saturation - oxygen saturation after the 6-min period (DeltaSat) during the 6MWT in patients with SSc, and to establish correlations between the 6MWT results and other clinical variables.

We analyzed 110 SSc patients. DeltaSat was defined as a fall of end-of-test saturation >or= 4%. Clinical and demographic data were collected. All the patients were submitted to chest radiographs and high-resolution CT (HRCT) and underwent pulmonary function testing and echocardiography, and the presence of autoantibodies was determined.

The variables associated with a walk distance < 400 m (p < 0.05) were age, dyspnea index, fibrosis on radiography, pulmonary arterial systolic pressure (PASP) >or= 30 mm Hg, and desaturation. The variables associated with DeltaSat (p < 0.05) were age, positive anti-Scl-70 autoantibody, dyspnea index, fibrosis on radiography, FVC < 80% of predicted, PASP >or= 30 mm Hg, and ground-glass or reticular opacities on HRCT. In the multivariate logistic regression analysis, three variables were significant when tested with walk distance: age, race, and dyspnea index; four variables were significant when tested with DeltaSat: age, dyspnea index, positive anti-Scl-70 autoantibody, and FVC < 80% of predicted.

Desaturation during a 6MWT provides additional information regarding severity of disease in scleroderma patients with pulmonary manifestations.