Evidence that large vessels do affect near infrared spectroscopy

Area of Science:

• Biomedical Engineering
• Physiology
• Medical Imaging

Background:

• Near infrared spectroscopy (NIRS) is widely used for non-invasive tissue oxygenation monitoring.
• The influence of large blood vessels on NIRS measurements is often assumed to be negligible.
• Understanding factors affecting NIRS accuracy is crucial for reliable physiological monitoring.

Purpose of the Study:

• To investigate the hypothesis that changes in large vessel size can significantly impact NIRS-derived blood volume indexes.
• To quantify the effect of venous volume changes on NIRS measurements over a major vein and surrounding muscle.
• To challenge the established assumption of negligible large vessel influence in NIRS.

Main Methods:

• Simultaneous NIRS and ultrasound monitoring were used in 11 subjects.
• Near infrared spectroscopy measured changes in total haemoglobin (tHb) and tissue haemoglobin index (THI).
• Ultrasound monitored the size of the basilic vein (BV) during slow and rapid venous occlusion.

Main Results:

• Both tHb and THI showed a significantly larger increase (1.7-4 fold) over the basilic vein compared to the biceps muscle.
• NIRS signals over the BV exhibited a stronger correlation with changes in BV size (r=0.91 for THI) than over the muscle (r=0.55).
• NIRS signals over the basilic vein demonstrated faster increases and greater convexity during venous occlusion.

Conclusions:

• Large veins, such as the basilic vein, significantly influence NIRS measurements of blood volume.
• The assumption that large vessels have a negligible impact on NIRS is challenged by these findings.
• Large veins may be a critical determinant of blood volume changes detected by NIRS in various experimental settings.