Abstract
BACKGROUND: Sensor-based estimation of six-minute walk distance and Cardiac Effort, number of heartbeats during the walk divided by distance walked, can be measured in the home. This study aimed to evaluate 1) the impact of walking course length on walk distance and Cardiac Effort, and 2) assess changes over time in a cohort of pulmonary hypertension and heart failure participants. METHODS: This was a prospective observational study conducted at two sites. Participants included pulmonary hypertension, heart failure, and healthy controls. All participants wore chest-based sensors capable of recording accelerometry and electrocardiographic data. At baseline visit, participants performed a six-minute walk test on both a 90-ft and a 30-ft course, separated by 30-minutes rest. Unsupervised home walk tests were performed on the following two days. All assessments were repeated eight weeks later. Walk distance and Cardiac Effort were measured using three methods: direct observation, lap count estimation, and a signal-derived method based on mean amplitude deviation. Comparisons between clinic and home-based measurements were made using paired t-tests, correlation analysis, and Bland-Altman testing. RESULTS: Sixty-six participants were enrolled, including 42 with pulmonary hypertension or heart failure and 24 controls. Walk distance on the 90-foot course was 10.7 percent longer than on the 30-ft course. Home-based walk distance was similar to the 30-ft course but lower than the 90-ft course. Home Cardiac Effort was similar to in-clinic values and tracked with changes over time. CONCLUSION: Home-based functional testing incorporating Cardiac Effort may offer a simple and effective remote metric to improve management of patients with heart failure.