Sub-maximal exercise testing in the assessment of interstitial lung disease secondary to systemic sclerosis: Reproducibility and correlations of the six minute walk test

Maya H Buch ¹, Christopher P Denton ², Daniel E Furst ³, Loic Guillevin ⁴, Lewis J Rubin ⁵, Athol U Wells ⁶, Marco Matucci-Cerinic ⁷, Gabriela Riemekasten ⁸, Paul Emery ⁹, Harbajan Chadha-Boreham ¹⁰, Pascal Charef ¹⁰, Sebastien Roux ¹⁰, Carol M Black ² and James R Seibold ^1*

¹ University of Michigan, United States
² Royal Free and University College Medical School, United Kingdom
³ UCLA School of Medicine, University of California, United States
⁴ Universite Rene Descartes, Paris, France
⁵ University of California, San Diego, United States
⁶ Royal Brompton Hospital, United Kingdom
⁷ University of Florence, Italy
⁸ Charite University Hospital, Berlin, Germany
⁹ University of Leeds, United Kingdom
¹⁰ Actelion, Switzerland

^* To whom correspondence should be addressed. E-mail: jseibold{at}umich.edu.

Accepted 15 July 2006

Abstract

Introduction: The six-minute walk test (6MWT) is increasingly utilised as an outcome measure in interstitial lung disease (ILD). The purpose of this study was to evaluate the usefulness of the 6MWT in a cohort of patients with ILD secondary to scleroderma (SSc) and to correlate with established physiological parameters.

Methods: 163 patients with SSc-ILD were recruited for a multi-centre, randomised, double-blind clinical trial. Available data at protocol screening included repeated six minute walk tests (6MWT), pulmonary function testing with diffusing capacity, Doppler echocardiography and high resolution computed tomography thorax. Borg dyspnoea index was evaluated pre- and post 6MWT.

Results: Mean distance walked during walk test 1 was 396.6m (SD 84.55m) compared with a mean of 399.5m (SD 86.28m) at walk test 2. The within subject, inter- test correlation as determined by Pearson correlation coefficient testing was 0.95 (p<0.0005). However, there were only weak correlations of 6MWT with percent forced vital capacity and the Borg dyspnoea index and no correlation was observed with percent diffusing capacity.

Conclusion: These data confirm the high reproducibility of the 6MWT in patients with SSc-ILD and therefore the validity of the test in this cohort. The lack of correlation of 6MWT with standard physiological parameters of interstitial lung disease suggests a multi- factorial basis for limited exercise capacity in SSc and calls into question the utility of the 6MWT as a measure of outcome in future studies of SSc-ILD.

Keywords: interstitial lung disease, scleroderma, six minute walk test, sub-maximal exercise test

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