A Cardiorespiratory Fitness Test for Acute Illness: Validity, Reliability, and Clinical Utility of Functional Incremental Stepping-in-Place Test

Abstract Survivors of hospitalization have an increased likelihood of developing physical disability after discharge, which is especially true for older patients, patients with pre-existing co-morbidities, and patients requiring mechanical ventilation. The six-minute walk test (6MWT) has been utilized as a chief outcome measure to examine functional exercise capacity in the acute hospitalization and post-discharge phases, but has several limitations in the hospital for clinical practice and research. Thus, our interdisciplinary team developed the Duke-Functional Incremental Step Test (DFIST) to address limitations to current testing paradigms. The DFIST has high clinical utility for the hospital setting including minimal equipment to administer, short administration time, and minimal space while maintaining components of gold standard cardiopulmonary exercise testing (CPET). Preliminary data on DFIST from ongoing randomized controlled trial demonstrate potential for strong construct validity when compared to 6MWT (n = 9, spearman rho = 0.65, p = 0.05). However, the validity of DFIST has not been prospectively examined in clinical patient populations. Therefore, the purpose of this multi-site prospective study is to assess the criterion and construct validity of DFIST compared to gold-standard CPET and physical functional testing. DFIST will be compared to gold-standard CPET - Bruce Ramp Protocol in a multi-site, cross-sectional analysis of subjects (n = 80). Subjects will perform the DFIST and Bruce Protocol with full metabolic cart. Secondarily, we will examine the content and construct validity as well as the clinical utility of DFIST in a diverse cohort of subjects. Specific to implementation science, we will evaluate timing of test, required length of training, adverse events, and early termination. The findings from this study will demonstrate that DFIST is a valid test for measuring cardiorespiratory fitness in diverse patient populations including hospitalized individuals and patients surviving ICU admission.