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Brain function requires oxygen and maintenance of brain capillary oxygenation is important. We evaluated how faithfully frontal lobe near-infrared spectroscopy (NIRS) follows haemoglobin saturation ( S Cap ) and how calculated mitochondrial oxygen tension ( P Mito O 2 ) influences motor performance. Twelve healthy subjects (20 to 29 years), supine and seated, inhaled O 2 air-mixtures (10% to 100%) with and without added 5% carbon dioxide and during hyperventilation. Two measures of frontal lobe oxygenation by NIRS (NIRO-200 and INVOS) were compared with capillary oxygen saturation ( S Cap ) as calculated from the O 2 content of brachial arterial and right internal jugular venous blood. At control S Cap (78% ± 4%; mean ± s.d.) was halfway between the arterial (98% ± 1%) and jugular venous oxygenation ( S V O 2 ; 61% ± 6%). Both NIRS devices monitored S Cap ( P 0.74; P < 0.05). These results show that NIRS is an adequate cerebral capillaryoxygenation-level-dependent (COLD) measure during manipulation of cerebral blood flow or inspired oxygen tension, or both, and suggest that motor performance correlates with the frontal lobe COLD signal.
Rasmussen et al. (Tue,) studied this question.