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Abstract
Over 4000 new cases of IPF are diagnosed each year with a poor prognosis and median survival time of 3 to 5 years. Assessments of exercise performance using the 6-minute walk test (6MWT) have been shown to be useful in predicting survival in a variety of pulmonary conditions.
Aim We wished to determine if indices of the six-minute walk test could predict survival in patients with IPF at one year and long-term survival.
Methods We undertook a retrospective data analysis of patients with a confirmed diagnosis of IPF over the last 4 years. Data was obtained on 86 patients, who were divided into Group 1 – survivors (n = 56) and Group 2 – non-survivors (n = 30).
Indices obtained from the 6MWT included SpO2, min, median SpO2 rest, BORG scores, HR,rest and HR,max and distance walked. Spirometry, static lung volumes, and date of death were also recorded. Data are presented as median (IQR) in the format (Group 1 vs Group 2). Kaplan-Meier analysis was used to compared various indices and between groups.
Results There was no significant differences between the two groups for FEV1 (2.0 (0.58) vs 2.01 (0.55)), FVC (2.83 (1.16) vs 2.52 (0.88)) or TLC (4.19 (1.58) vs 4.09 (1.62)). From the 6 MWT, SpO2,rest was not significantly different (95 (2) vs 94 (5.5)), nor were HRrest, HRmax or BORG scores.
There was a significant difference for SpO2, min (90 (8) vs 84 (13); p < 0.01) and distance walked (380 (140) vs 340 (180); p < 0.05). Kaplan-Meier analysis was used to assess outcomes for distance walked of < or >250 m and 350 m and SpO2, min < or >85% and 88%.
Kaplan-Metre survival curve for SpO2 min <88% (red line) and >88% (blue line). The green dashed line plotted shows survival of 365 days of 90%. The bkue and red dotted lines are the 95% confidence interval for survival.
For an SpO2, min cut-off of 85%, survival was 791 (<85%) and 1181 (>85%) days (p < 0.05; hazard ratio 3.356). With a cut-off of 88%, survival was 757 (<88%) and 1272 (>88%) days (p = 0.0012; hazard ratio 3.161). Survival at one year as 84% (<88%) and 91% (>88%) (Figure).
Distanced walked was not significantly different at cut-offs of 250 m or 350 m.
Conclusions From this retrospective analysis, these results suggest that a cut-off for SpO2, min of 88% may be a useful predictor of survival at one year and in the longer term. Distance walked appears to contribute little to prediction of survival.