Quantitative analysis of tissue oxygenation variability across anatomical landmarks in healthy individuals via near-infrared spectroscopy

Near-infrared spectroscopy (NIRS) enables noninvasive assessment of tissue oxygenation, but its broader clinical application is hindered by the absence of standardized reference values across anatomical regions. This study aimed to characterize baseline regional tissue oxygen saturation (rSO₂) across 17 anatomical landmarks in healthy adults and to identify the most consistent and reproducible measurement sites. Seventy-eight healthy participants (mean age 31 ± 13.4 years) underwent rSO₂ assessments using a continuous-wave NIRS system. Demographic and physiological data, including age, sex, skin pigmentation, tissue thickness, and mean arterial pressure, were collected. rSO₂ values ranged from 50.5 to 86.0%, with most values between 65 and 76%. The temporomandibular joint and mandibular ramus had the highest mean rSO₂ (~ 75.8%), while the thenar eminence and forehead showed the lowest. The quadriceps exhibited the lowest inter-individual variability (2.72 SD), making it the most reliable site for baseline measurements. The sternum also showed low variability (2.96 SD), suggesting its usefulness in dynamic monitoring. Age and sex significantly influenced rSO₂ (p < .001), while other variables had limited impact. These findings establish normative rSO₂ values and identify optimal NIRS placement sites, supporting device-specific measurement in clinical and research applications to improve detection of tissue hypoxia and perfusion abnormalities.