The effects of normoxia, hypoxia, and hyperoxia on cerebral haemoglobin saturation using near infrared spectroscopy during maximal exercise

At rest, cerebral haemoglobin saturation (ScO2), obtained with near infrared spectroscopy (NIRS), tracks the calculated capillary-oxygenation-level-dependent (COLD) signal. However, the relationship between the two variables during maximal exercise is unknown. We evaluated ScO2 by dual wavelengths NIRS (Somanetics INVOS) and calculated mean cerebral capillary oxygen saturation (ScapO2) during maximal ergometer rowing in six subjects in normoxia, hypoxia (17% inspired O2) and hyperoxia (30% O2). We determined middle cerebral artery blood flow velocity by 2 MHz transcranial ultrasound Doppler, arterial (SaO2) and internal jugular venous O2 saturation (SvO2). Maximal rowing reduced SaO2, SvO2 and ScapO2 (P < 0.05) with no significant changes in ScO2 compared to rest. Hyperoxia prevented, while hypoxia aggravated, the reductions in SaO2 and SvO2 (P < 0.05). Across the range of inspired O2, SaO2 varied from 88.6 ± 2.4 to 98.3 ± 0.4% (mean ± SD), SvO2 from 49.4 ± 8.4 to 64.4 ± 5.6%, and ScapO2 from 68.2 ± 0.5 to 81.1 ± 0.5% while the changes in ScapO2 were tracked by ScO2 (r2 = 0.31; P < 0.01) with values for ScO2 (63.8 ± 11.7%) being lower than those for ScapO2 (76.7 ± 6.0%; P < 0.05). The present data suggest that during maximal exercise ScO2, though influenced significantly by venous blood, maintains a tight coupling with the calculated ScapO2.Relevance to industryPersonnel working in industrial environments with low ambient oxygen partial pressure or high temperatures may face premature exhaustion from cerebral fatigue caused by low cerebral oxygenation. As cerebral oxygenation can be measured non-invasively during the vigorous movements associated with ergometer rowing, it can also be applied for field studies, e.g. during work in special environments including high altitude and high ambient pressure or temperature.