Relationship between outcome measures of six-minute walk test and baseline lung function in patients with interstitial lung disease.

BACKGROUND AND AIM OF THE WORK: In patients with interstitial lung disease (ILD), the six-minute walk test (6MWT) has been rarely used, and up till now, the relationship between outcome measures of the test and baseline lung function has not yet been examined. Therefore, we assessed walk distance, oxygen desaturation, and breathlessness perception during 6MWT, and their relationships to baseline lung function in patients with ILD.
METHODS: Forty ILD patients with history of breathlessness during physical exertion performed a 6MWT following a standard protocol. Breathlessness perception during walk was assessed by visual analogue scale (VAS, in mm).
RESULTS: The mean walk distance was 487 meters (range 271-689). Mean baseline oxygen saturation (Base SpO2, %) was 94% and was reduced during walk, either as mean oxygen saturation (Mean SpO2, 89%, p < 0.001) or as mean fall in oxygen saturation during walk (Fall SpO2, 5%). Furthermore, VAS significantly increased after walk (5 mm to 44 mm, p < 0.001). A close relationship of TLco and TLC to walk distance and Fall SpO2 was found (r = 0.45 and 0.42 and r = -0.75 and -0.64, respectively; p < 0.001, each). On the basis of regression equations by stepwise multiple regression analysis, walk distance was predicted by age and FVC (r2 = 0.50), Mean SpO2 by TLco and Base SpO2 (r2 = 0.80), and Fall SpO2 only by TLco (r2 = 0.57). Breathlessness perception was not reliably predicted by any assessed variables.
CONCLUSIONS: We confirmed that 6MWT provides a global evaluation of sub-maximal exercise capacity in ILD patients. We also found that walk distance and oxygen desaturation, but not breathlessness perception during walk, are strictly related to baseline lung function.