Wearable tissue oximetry during standardized physiological stressors in chronic heart failure outpatients

Background: Outpatient chronic heart failure (HF) assessment relies on NYHA class and distance-based testing that can obscure physiological heterogeneity. Near-infrared spectroscopy (NIRS) enables tissue oxygenation phenotyping but is underexplored during standardized stressors in outpatient HF. We tested whether wearable NIRS-derived oxygenation kinetics during a vascular occlusion test (VOT) and six-minute walk test (6MWT) differ across NYHA classes. Methods: In this prospective, single-center pilot study, 44 chronic HF outpatients (mean age 70.9 {+/-} 8.7 years, 75% male; NYHA I [n=19], II [n=12], III [n=13]) were monitored with a novel wearable NIRS device (NIRSense Envello Core) during a VOT and 6MWT. Primary endpoints were the post-occlusion net area under the curve (net AUC; VOT) and post-walk recovery net AUC (modified 6MWT). Secondary endpoints included the exertional tissue oxygenation (Oxy) nadir, VOT reperfusion kinetics, gait metrics, and tolerability. Results: Despite NYHA I and II walking identical median distances (420 m), post-walk recovery net AUC was lower in NYHA II (-16.3 a.u.xs) and III (-12.8 a.u.xs) than NYHA I (46.1 a.u.xs, p=0.004). The exertional Oxy nadir did not differ (p=0.722), but NYHA III walked 27% and 38% slower than NYHA II and I (p<0.001). NYHA II had higher VOT net AUC (134.2 a.u.xs) than NYHA I (71.9; p=0.018) and III (61.1; p=0.011). Post-walk recovery net AUC correlated with gait velocity (rs=0.44) and distance (rs=0.39; both p<0.05). VOT net AUC did not correlate with functional metrics, but resting reperfusion kinetics correlated with 6MWT performance (rs=0.41-0.46, p<0.05). The sensor was well tolerated. Conclusions: Wearable NIRS-derived recovery kinetics differentiated NYHA I from NYHA II despite these classes walking identical median distances. Coupled with distinct resting VOT hyperemic differences, these preliminary findings indicate wearable NIRS may capture physiological heterogeneity in outpatient HF not reflected by NYHA class and standard functional metrics.