Capillary-Oxygenation-Level-Dependent Near-Infrared Spectrometry in Frontal Lobe of Humans

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Abstract
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 ( SCap) and how calculated mitochondrial oxygen tension ( PMitoO2) influences motor performance. Twelve healthy subjects (20 to 29 years), supine and seated, inhaled O2 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 ( SCap) as calculated from the O2 content of brachial arterial and right internal jugular venous blood. At control SCap (78% ± 4%; mean ± s.d.) was halfway between the arterial (98% ± 1%) and jugular venous oxygenation ( SVO2; 61% ± 6%). Both NIRS devices monitored SCap ( P < 0.001) within ~5% as SvO2 increased from 39% ± 5% to 79% ± 7% with an increase in the transcranial ultrasound Doppler determined middle cerebral artery flow velocity from 29 ± 8 to 65 ± 15 cm/sec. When SCap fell below ~70% with reduced flow and inspired oxygen tension, PMitoO2 decreased ( P < 0.001) and brain lactate release increased concomitantly ( P < 0.001). Handgrip strength correlated with the measured (NIRS) and calculated capillary oxygenation values as well as with PMitoO2 ( r > 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.