In a 44-patient pilot study of chronic heart failure outpatients (mean age 70.9 years), wearable near-infrared spectroscopy (NIRS) revealed striking physiological differences invisible to standard functional testing. NYHA Class I and II patients walked identical median distances (420 m), yet post-walk tissue oxygenation recovery net AUC diverged sharply: 46.1 a.u.×s for Class I versus −16.3 for Class II (p=0.004). Resting vascular occlusion test reperfusion kinetics also correlated significantly with 6MWT performance (rs=0.41–0.46), suggesting microvascular dysfunction is detectable at rest before functional decline becomes apparent.
The finding matters because NYHA classification and distance-based walk tests are the clinical workhorses for heart failure stratification, yet they notoriously compress physiological heterogeneity — a patient can walk 420 meters and still harbor meaningfully impaired microvascular reserve. NIRS-derived oxygenation kinetics may expose that hidden deficit, potentially enabling earlier intervention or more precise risk stratification. This aligns with growing interest in microvascular phenotyping across cardiometabolic disease, where impaired tissue oxygen delivery precedes overt functional decline. Limitations are substantial: single-center, 44 patients, pilot design, no outcomes data, and no female-majority representation (75% male). The non-linear VOT finding in Class II warrants cautious interpretation. Crucially, this is a preprint posted to medRxiv and has not yet been peer-reviewed — findings may change materially after expert scrutiny. Currently incremental in scope but potentially paradigm-shifting in clinical workflow if validated in larger, outcomes-linked cohorts.
