Real-Time Monitoring of Tissue Oxygenation During Hyperbaric Oxygen Exposure Using In Vivo EPR Oximetry

Hyperbaric oxygen (HBO) therapy increases blood oxygen levels by exposing patients to 100% oxygen under elevated pressure and is used clinically for conditions such as decompression sickness, carbon monoxide poisoning, chronic wounds, and impaired tissue healing. However, real-time precise and quantitative measurement of tissue oxygen tension (pO₂) under hyperbaric conditions remains technically very challenging.

We developed a specialized small-animal hyperbaric chamber compatible with in vivo electron paramagnetic resonance (EPR) oximetry using customized OxyTrack oxygen detectors. Up to two detectors were implanted simultaneously to measure pO₂ in skeletal muscle and tumor tissue in mice. Animals were exposed to air (21% O₂) and 100% O₂ at both normobaric pressure and 2 atmospheres absolute (ATA) in a stepwise protocol.

The chamber operated safely and stably up to 2 ATA, enabling continuous real-time pO₂ monitoring without adverse events and issues with the hardware for up to 90 min. In B16-F10 melanoma, tumor pO₂ increased from ∼9 mmHg at baseline to ∼26 mmHg at 100% O₂ (1 ATA) and ∼50 mmHg at 2 ATA, with partial retention after decompression. In contrast, SCC7 tumors showed minimal responsiveness (∼9-10 mmHg), whereas skeletal muscle demonstrated marked pressure-dependent increases (up to ∼50 mmHg).

The small-animal HBO chamber enables real-time, tissue-specific assessment of oxygen dynamics under clinically relevant hyperbaric conditions. The approach could facilitate optimization of HBO protocols and support translational investigation of oxygen-modulated therapies, including radiation and drug responses in solid tumors.