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

摘要

At rest, cerebral haemoglobin saturation (S_cO_2), 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 S_cO_2 by dual wavelengths NIRS (Somanetics INVOS) and calculated mean cerebral capillary oxygen saturation (S_(cap)O_2) during maximal ergometer rowing in six subjects in normoxia, hypoxia (17% inspired O_2) and hyperoxia (30% O_2). We determined middle cerebral artery blood flow velocity by 2 MHz transcranial ultrasound Doppler, arterial (S_aO_2) and internal jugular venous O_2 saturation (S_vO_2). Maximal rowing reduced S_aO_2, S_vO_2 and S_(cap)O_2 (P<0.05) with no significant changes in S_cO_2 compared to rest. Hyperoxia prevented, while hypoxia aggravated, the reductions in S_aO_2 and S_vO_2 (P < 0.05). Across the range of inspired O_2, S_aO_2 varied from 88.6 ± 2.4 to 98.3 ± 0.4% (mean ± SD), S_vO_2 from 49.4 ± 8.4 to 64.4 ± 5.6%, and S_(cap)O_2 from 68.2 ± 0.5 to 81.1 ± 0.5% while the changes in S_(cap)O_2 were tracked by S_cO_2 (r~2 = 0.31; P<0.01) with values for S_cO_2 (63.8 ± 11.7%) being lower than those for S_(cap)O_2 (76.7 ±6.0%; P<0.05). The present data suggest that during maximal exercise S_cO_2, though influenced significantly by venous blood, maintains a tight coupling with the calculated S_(cap)O_2. Relevance to industry: Personnel 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.