The six-minute walk test using forehead oximetry is reliable in the assessment of scleroderma lung disease

The six-minute walk test (6MWT) is a validated field test in the assessment of interstitial lung disease but may not be so useful in scleroderma (SSc) lung disease. The aim of this study was to determine the reliability of the 6MWT in patients with SSc and correlate results with morphological and functional measures of disease severity.

Thirty patients (24 female, mean age 47, mean diffusing capacity of carbon monoxide 65%, vital capacity 77% predicted) with American College of Rheumatology classification of SSc performed two 6MWT using various oximetry sites, 1 week apart, and underwent SSc-specific disease severity and quality-of-life measurements, lung function, high-resolution computed tomography and echocardiography.

There was good reliability between the two 6MWT (distance; intraclass correlation coefficient 0.95, r = 0.89, Borg; intraclass correlation coefficient 0.85, r = 0.91, both P < 0.00 for r), and Bland Altman plots demonstrate good agreement between measures 1 week apart. Forehead and finger oximetry were more reliable than earlobe (intraclass correlation coefficient 0.64, 0.60, 0.24; r = 0.46, 0.47, 0.14; n = 22, 17, 7, respectively). Forehead desaturation correlated with forced expiratory volume in 1 s (r = 0.55, P = 0.01) and forced vital capacity (r = 0.59, P = 0.01). Distance correlated with all physiological measures: forced expiratory volume in 1 s (r = 0.55, P = 0.01), forced vital capacity (r = 0.61, P = 0.01) and diffusing capacity of carbon monoxide (r = 0.42, P = 0.05). Computed tomography extent and patterns of disease correlated poorly with 6MWT measures, and global measures of SSc correlated only with post-test Borg score.

The 6MWT is feasible and reliable in SSc lung disease, but forehead oximetry should be used. The test measurements correlate reasonably but variably with functional and morphological measures of disease severity.