Continuous, noninvasive, and localized microvascular tissue oximetry using visible light spectroscopy

Area of Science:

• Biomedical Engineering
• Physiology
• Medical Diagnostics

Background:

• Visible light spectroscopy (VLS) oximetry measures microvascular hemoglobin oxygen saturation (StO2) using shallow-penetrating visible light.
• Unlike other methods, VLS oximetry analyzes small, thin tissue volumes for localized oxygenation.
• This technique offers a novel approach to assessing tissue oxygen levels.

Purpose of the Study:

• To evaluate the efficacy of VLS oximetry in detecting hypoxemia and ischemia in both human and animal models.
• To compare VLS oximetry with existing methods like pulse oximetry (SpO2).
• To establish the reliability and reproducibility of StO2 measurements at various tissue sites.

Main Methods:

• StO2 measurements were taken in pigs and human patients across different physiological states: normoxia, hypoxemia, and ischemia.
• Tissue sites included muscle, skin, and oral/enteric mucosa.
• Ischemia was induced via occlusion, compression, or cardiac arrest, while hypoxemia was induced by controlled reduction of SpO2.

Main Results:

• VLS oximetry demonstrated significant decreases in StO2 during hypoxemia and ischemia in both animal and human subjects.
• StO2 measurements correlated strongly with SpO2 during hypoxemia (r2 = 0.98 in animals, r2 = 0.87 in humans).
• Ischemia was reliably detected by a widened pulse/VLS saturation difference (Delta > 35%).

Conclusions:

• VLS oximetry provides continuous, noninvasive, and localized StO2 measurements.
• The technique is sensitive to hypoxemia and both regional and global ischemia.
• Oral/enteric mucosa offers a reliable reference site for VLS monitoring of systemic flow due to its reproducible normal StO2 range.