Six-minute walk distance and survival time in patients with idiopathic pulmonary fibrosis in Brazil

Abstract

Objective:To determine the cut-off point for the six-minute walk distance (6MWD) that indicates lower survival time in patients with idiopathic pulmonary fibrosis (IPF) in Brazil. Methods:This was retrospective study carried out in two referral centers for IPF. The 6MWT was performed twice, considering the highest value of the 6MWD. Various cut-off points were estimated, in absolute values and in percentage of predicted values, using ROC curves, the Kaplan-Meier method, and data from other studies. Results:The sample comprised 70 patients with IPF. The mean age was 71.9 ± 6.4 years, and 50 patients (71.4%) were male. The mean FVC was 76.6 ± 18.2% of predicted value. The mean SpO2 at rest before and after 6MWT were 93.8 ± 2.5% and 85.3 ± 6.5%, respectively. The median survival time was 44 months (95% CI: 37-51 months). The mean 6MWD was 381 ± 115 m (79.2 ± 24.0% of predicted). After the analyses, the best cut-off points for estimating survival were 6MWD < 330 m and < 70% of predicted. The median survival time of patients with a 6MWD < 330 m was 24 months (95% CI: 3-45 months), whereas that of those with a 6MWD ≥ 330 m was 59 months (95% CI: 41-77 months; p = 0.009). Similarly, the median survival times of those with a 6MWD < 70% and ≥ 70% of predicted, respectively, were 24 months (95% CI: 13-35 months) and 59 months (95% CI: 38-80 months; p = 0.013). Cox multivariate regression models including age, sex, smoking status, SpO2 at the end of the 6MWT, and FVC% showed that 6MWD remained significantly associated with survival (p = 0.003). Conclusions:Values of 6MWD < 330 m and < 70% of predicted value were associated with lower survival time in IPF patients in Brazil.

Six-minute walk test in patients with idiopathic pulmonary fibrosis

“…It appears that such an association also applies to respiratory diseases such as COPD and IPF. However, the difference between the values found by Mancuso et al 10 and those found by other authors might be due to the study design and the analyses performed in the study. Because it is impossible to compare the study conducted by Mancuso et al 10 with all previous studies, I will compare it with the study involving the highest number of patients and based on data from the study by du Bois et al 7 …”

“…The first question is why the indicator of poor prognosis found in a study conducted in Brazil 10 is significantly different from those found in studies conducted elsewhere. 7 , 11 - 13 According to Mancuso et al, 10 this might be due to differences in reference values for the 6MWT across countries. 14 There is evidence that the 6MWD is longer in individuals living in Latin America than in those living in Europe or the USA.…”

“…In the current issue of the JBP, Mancuso et al 10 report the 6MWD in 70 IPF patients retrospectively selected from among those treated at either of two referral centers for interstitial lung disease in Brazil. The major finding of the study is that a 6MWD of < 330 m or < 70% of the predicted value is associated with a substantially decreased survival rate and should be considered an indicator of poor prognosis in patients with IPF in Brazil.…”

“…In the study by Mancuso et al, 10 patients presenting with an SpO 2 of < 89% were excluded, whereas, in the study by du Bois et al, 7 11.5% of the participants were receiving oxygen therapy. The difference in findings between the two studies might be explained, at least in part, by the fact that the latter study included patients who were more severely ill, including patients with severe pulmonary hypertension.…”

Prognostic Value of Cardiopulmonary Exercise Test, Pulmonary Function Test , and Questionnaires on Mortality in Patients With Idiopathic Pulmonary Fibrosis: A Prospective Pilot Study

“…[8][9][10][11] 6MWT is a commonly used surrogate test to predict outcomes in patients with IPF. In 6MWT, the distance walked in 6 min, [22] decrease in the distance walked at 24 weeks, [13] recovery of heart rate after 1 min of the test, [23] and oxygen desaturation [24] are associated with increased mortality in patients with IPF. Gender, age, and the two physiologic variables in PFT "FVC" and "DLCO" have been recently integrated into the gender, age and pulmonary physiology (GAP) index, [25] which can also precisely predict the survival rate in patients with IPF.…”