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

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 < 0.001) within ~5% as S v O 2 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 S Cap fell below ~70% with reduced flow and inspired oxygen tension, P Mito O 2 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 P Mito O 2 ( 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.