Fig. 1

Correlation between 6-min walk test distance (6MWD) and FVC% (a) or DLco% (b) for all IPF patients diagnosed with severe functional impairment (FVC ≤ 50% and/or DLco ≤ 30% predicted) based on the need for supplemental oxygen at exercise (\({\text{6MWT}}_{{{\text{O}}_{{2}} }}\), red) or not (6MWT_RA, blue). 6MWD: 6-min walk test distance, meters; FVC%: forced vital capacity, % predicted; DLco%: single breath diffusing capacity for carbon monoxide, % predicted; 6MWT_RA: patients able to complete a 6MWT with SpO₂ > 86% on room air; \({\text{6MWT}}_{{{\text{O}}_{{2}} }}\): patients with need for supplemental oxygen during 6MWT