Gait speed, measured by the four meter gait speed (4MGS) test, is an independent predictor of all-cause mortality and hospitalization in patients with idiopathic pulmonary fibrosis (IPF), according to a recent study. The tool could be used as a prognostic approach to select cohorts in clinical trials, optimize trial endpoints, and identify high-risk patients.
The study, “Gait speed and prognosis in patients with idiopathic pulmonary fibrosis: a prospective cohort study,” was published in the European Respiratory Journal.
The choice of clinical trial endpoints is key to performing successful clinical trials assessing IPF rehabilitation, prognosis, and patient mortality. But conflicting opinions and the use of different approaches impede optimization of trial endpoints.
Pulmonary function assessments, such as forced vital capacity (FVC), are currently being used as endpoint surrogates in clinical trials. But although FVC correlates with worsened fibrosis, results are sometimes inconsistent between readings, and patient mortality is not always linked with worsened FVC values. Also, because of its measurement approach, IPF-related symptoms such as coughing, dyspnea (shortness of breath), or infections might skew the data.
The team previously showed that gait speed — independent of lung function — is a reliable tool associated with different clinical outcomes in IPF patients, including exercise capacity and dyspnea. To evaluate it further as a prognostic tool, researchers investigated the association between 4MGS and IPF patient survival and hospitalization.
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Researchers enrolled 130 patients newly diagnosed with IPF, and measured baseline 4MGS and lung function. Patient survival and emergency (non-elective) hospital admissions were assessed over one year.
Patients were recruited from respiratory clinics at the Royal Brompton and Harefield Hospital NHS Foundation Trust in the U.K. The majority were male (83%) with a mean age of 72 years.
4MGS was “assessed on a flat, unobstructed four meter course by trained staff,” the researchers stated. In the test, the speed at which patients complete the track is assessed.
4MGS was recorded as a continuous variable (measured in seconds) or as a binary variable (measured as slow versus preserved gait speed). Slow gait speed was set as less than 0.8 meters per second, which is an internationally established threshold that can predict adverse outcomes, including in IPF.
Results showed that both continuous and slow 4MGS data showed significant and independent association with hospitalization and survival of IPF patients.
Although FVC was found to be an independent predictor of mortality, including 4MGS as a variable in further analyses improved its predictive ability. Also, contrary to 4MGS, FVC assessment was not an independent predictor of IPF patient hospitalization.
Finally, researchers compared the predictive capacity for mortality of the 4MGS test with two common models for predicting IPF patient mortality and prognosis based on lung function — the gender and age physiology (GAP) index, and the composite physiologic (CPI) index.
Results showed that 4MGS was a better predictor of mortality compared with either GAP or CPI.
The team concluded, “Our data suggest that 4MGS may have potential as a stratification tool of adverse outcomes in IPF. Depending on purpose, 4MGS could be used to enrich or deplete a clinical trial cohort with those at high risk of adverse outcome, or to balance treatment arms at baseline.”
According to the team, slow 4MGS in particular may be a reliable surrogate for clinical trial endpoints, as gait speed changes could indicate adverse clinical outcomes. In addition, gait speed could also be used to assess patient improvement upon disease interventions, such as pulmonary rehabilitation.
“Our study is the first to assess the prognostic validity of 4MGS, and the first to demonstrate that 4MGS is an independent predictor of all-cause mortality and all-cause, non-elective hospitalization in IPF,” the researchers said. “We propose that 4MGS has potential as a stratification tool of adverse outcomes for use in research and clinical settings.”