Tissue oxygenation measured with near-infrared spectroscopy during normobaric and hyperbaric oxygen breathing in healthy subjects

To evaluate the possibility of using near-infrared spectroscopy (NIRS) to measure tissue oxygenation (StO₂) during hyperbaric oxygen (HBO) therapy. Nine healthy volunteers (1 female) age 25−37 years, breathed air or oxygen. Tissue oxygenation was measured using NIRS on the thumb. Subjects were blinded to breathing gas. A range of partial pressures of oxygen were administered in 10-min intervals: 21, 101, 21 kPa (compression to 280 kPa), 59, 280, 59 (decompression), 21 kPa. Data were averaged over last 5 min at each pressure. When switching from air to normobaric oxygen (NBO 101 kPa) StO₂ increased from 83% (82−85%, median and interquartile range) to 85% (84−87%) (P < 0.01), while when switching from air at pressure (59 kPa O₂) to HBO (280 kPa), StO₂ increased from 85% (85−86%) to 88% (87−89%) (P < 0.001). There was no difference between baseline StO₂ while air breathing before NBO or after decompression. Values did not reach the maximal value of 100% at any point. The changes in hemoglobin oxygen saturation in tissue registered by the NIRS monitor when switching from air to oxygen followed inspired PO₂ under normobaric and hyperbaric conditions.