Continuous Site-Specific Intravascular Monitoring of Arterial and Venous Blood Oxygenation In Vivo

OBJECTIVE: Conventional pulse oximetry provides continuous non-invasive arterial oxygen saturation, whereas arterial and venous blood gas analysis provides intermittent reference measurements. Neither modality continuously monitors saturation at a selected deep intravascular site. In this proof-of-concept feasibility study, we assessed whether intravascular diffuse reflectance spectroscopy tracks the direction and time course of prespecified arterial, central venous, and regional renal venous oxygenation changes, alongside conventional pulse oximetry where an arterial comparator was appropriate. Approach. Three separate experimental protocols were performed in three pigs (one animal per protocol; n=1 per condition). Oxygen saturation was monitored with the iBLOS sensing wire in the abdominal aorta during apnea-induced systemic hypoxemia, in the inferior vena cava (IVC) during repeated hypoxic challenges, and in the right renal vein during transient venous outflow obstruction. Conventional pulse oximetry was recorded concurrently during the arterial and IVC protocols as an arterial monitoring comparator; no blood-gas samples were collected in these feasibility experiments. Main results. Continuous intravascular blood oxygenation level monitoring detected rapid and dynamic arterial desaturation and reoxygenation during systemic apnea and demonstrated reproducible responses during repeated hypoxic challenges. Venous oxygenation measured in the inferior vena cava exhibited lower baseline oxygen saturation and slower desaturation-recovery kinetics than arterial measurements, reflecting physiological oxygen extraction and circulatory transit delays. During renal vein occlusion, oxygen saturation proximal to the obstruction progressively decreased toward near-complete oxygen depletion before rapidly recovering following restoration of venous outflow. These regional physiological measurements are not feasible using peripheral pulse oximetry. Significance. This feasibility platform provides continuous, site-specific intravascular saturation trends in vascular territories that conventional non-invasive monitoring cannot directly sample. With validation against contemporaneous blood-gas measurements and evaluation in larger studies, it could help fill a monitoring gap during ischemia, reperfusion, and endovascular intervention. .