Near-Infrared Spectroscopy Demonstrates Preserved and Reproducible Resting Skeletal Muscle Oxygenation Across Anatomical Sites in Stable Heart Failure

Background: Near-infrared spectroscopy (NIRS) enables non-invasive assessment of regional tissue oxygenation (StO 2 ). Although impaired skeletal muscle oxygenation during stress is well documented in heart failure (HF), the reproducibility of resting StO 2 and its potential utility for clinical monitoring remain unclear. Methods: Twenty adults (ten healthy; ten chronic HF) underwent StO 2 assessment using the Medtronic INVOS TM 7100 system at five sites: pectoralis major, deltoid, biceps, flexor carpi, and rectus femoris. Duplicate measurements were obtained over one minute with sensor repositioning between recordings. Effects of time and group were evaluated using general linear models. Reproducibility was assessed using intraclass correlation coefficients (ICCs) and Bland-Altman analyses (p<0.05). Results: Resting StO 2 was similar between healthy participants and those with HF across all anatomical sites (pectoralis major: p=0.73; deltoid: p=0.71; biceps: p=0.12; flexor carpi: p=0.20; rectus femoris: p=0.32). No significant effects of time, group, or group-by-time interactions were observed (all p > 0.10), except for a small increase in biceps StO 2 in HF (p=0.04). Reproducibility remained high following sensor repositioning, with strong ICCs across all sites (all > 0.84; p < 0.001) and minimal bias on Bland-Altman analyses. Conclusion: Resting skeletal muscle StO 2 measured by NIRS is preserved and highly reproducible across anatomical sites in stable HF, despite inherent microvascular and oxygen delivery abnormalities. These findings support the feasibility of NIRS for longitudinal StO 2 monitoring. However, resting StO 2 alone do not discriminate HF status, suggesting that NIRS may may have greater clinical utility for detecting dynamic changes during physiological stress or acute HF decompensation.