PURPOSE:Idiopathic pulmonary fibrosis (IPF) is a progressive condition with an unpredictable rate of functional decline. While static measures, such as six-minute walk tests (6MWT) and spirometry have been used, they do not reliably measure functional deteriorations or predict outcomes. We sought to determine if the rate of decline would better predict and time mortality than static measures of these variables.
METHODS:Retrospective review of patients with biopsy-proven IPF and two or more evaluations, followed until death, transplant, or end of the observation period. From each encounter we abstracted patient demographics, spirometric values, and 6MWT parameters. 6MWT parameters included distance walked (in meters), oxygen saturation nadir and the distance-saturation product (product of the distance walked and SpO2 nadir). We identified predictors of death using Cox proportional hazard models.
RESULTS:77 subjects were included (77.9% male, mean age 61±11 years). Mean follow-up time was 34 ± 25 months. During the observation the period, there were 30 (39%) survivors and 47 (61%) deaths. Six (7.8%) underwent lung transplantation. All measured variables declined over time. However, the rate of decline was greater among non-survivors and increased as death approached. Of these variables, the distance-saturation product was the most accurate predictor of outcomes. The only independent predictors of death were the final distance-saturation product (HR=0.995; 95%CI= 0.992–0.997) and slope of decline in the distance-saturation product (HR=1.58; 95%CI=1.03–2.40).
CONCLUSION:Functional impairment is common and often progressive in IPF. The rate of decline in the distance-saturation product is a simple tool that independently predicted mortality. Our data suggests that as patients approach death the rate of decline in the distance-saturation product accelerates.
CLINICAL IMPLICATIONS:The rate of decline in 6MWT parameters, especially the distance-saturation product, may add further prognostic value and assistance in the timing of lung transplantation.
DISCLOSURE:James Woodrow, No Financial Disclosure Information; No Product/Research Disclosure Information