Capillary-oxygenation-level-dependent nearinfrared 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 (PMitoO2) 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 ( SCap) as calculated from the O2 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 ( SvO2; 61% +/- 66%). Both NIRS devices monitored SCap (P < 0.001) within similar to 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 +/- 15cm/sec. When SCap fell below similar to 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.