Four-meter gait speed predicts mortality in IPF
AT ATS 2018
SAN DIEGO – Among patients with idiopathic pulmonary fibrosis (IPF), an improvement in 4-meter gait speed with pulmonary rehabilitation is an independent predictor of all-cause mortality at 1 year, suggest results from a multicenter study presented at an international conference of the American Thoracic Society.
In all, 11% of patients died within 1 year of completing pulmonary rehabilitation.
“Mortality is an attractive endpoint in IPF clinical research but requires large sample sizes and long follow-up duration, making clinical trials expensive and challenging to undertake,” lead study author Claire M. Nolan, MSc, said at the conference.
“Consequently, there is much interest in surrogate endpoints of mortality. In the elderly population, a lot of work has been done on performance measures, in particular the 4-meter gait test. It’s a simple test to do from the assessor’s perspective, because you just need a 4-meter corridor and a stopwatch. From the patient’s perspective, they only have to walk at their usual speed, making it feasible in most settings.”
The study by Ms. Nolan, a National Institute for Health Research fellow, and her associates, involved recruiting 90 IPF patients referred to three outpatient pulmonary rehabilitation programs in London. All patients underwent the following assessments before and after 8 weeks of pulmonary rehabilitation: spirometry; Medical Research Council dyspnea score; anthropometry; 4-meter gait speed; incremental shuttle walk test, and King’s Brief Interstitial Lung Disease questionnaire. Ms. Nolan, a respiratory physiotherapist with the Harefield Pulmonary Rehabilitation and Muscle Research Group, Royal Brompton and Harefield NHS Foundation Trust, Harefield, London, and her associates drew from national databases to obtain data on all-cause mortality 1 year following pulmonary rehabilitation.
“We also identified a cutpoint, so if patients improved their walking speed by 0.009 meters per second or above, that was associated with a longer survival time at 1 year (area under the curve of 0.76, for sensitivity of 69.6% and a specificity of 70%; P less than 0.01),” she said.* “Among patients who achieved that cutpoint or exceeded it, only 5% of them died in the 1-year follow-up period, compared with 23% in the group that didn’t achieve that cutpoint. That’s quite a big difference, but this requires external validation in another population.”
To determine the 4-meter gait speed change cut-off that best discriminated between patients who died and survived, the investigators plotted receiver operating characteristic curves. For validation, they conducted a Kaplan-Meier analysis to assess time to death, with significance assessed via the log-rank test. Finally, they used a multivariate Cox proportional hazards model to characterize the relationship between 4-meter gait speed change and all-cause mortality, adjusting for independent predictors of mortality (age, previous respiratory hospitalizations in the past year, forced vital capacity percent predicted) and baseline 4-meter gait speed.
At baseline, 70% of the 90 patients were male, mean age was 74 years, mean forced vital capacity was 72.8% predicted, and mean Medical Research Council dyspnea score was 3. In addition, mean body mass index was 27.2 kg/m2, mean 4-meter gait speed was 0.92 meters per second, mean incremental shuttle walk test measurement was 271 meters, and mean King’s Brief Interstitial Lung Disease total score was 56.4. Following 8 weeks of pulmonary rehabilitation, the patients’ 4-meter gait speed improved significantly by a mean of 0.15 meters per second (P less than .001). All other variables also improved significantly, with the exception of forced vital capacity.
