Near-infrared spectroscopic quantification of changes in the concentration of oxidized cytochrome c oxidase in the healthy human brain during hypoxemia

Abstract

The near-IR cytochrome c oxidase (CCO) signal has potential as a clinical marker of changes in mitochondrial oxygen utilization. We examine the CCO signal response to reduced oxygen delivery in the healthy human brain. We induced a reduction in arterial oxygen saturation from baseline levels to 80% in eight healthy adult humans, while minimizing changes in end tidal carbon dioxide tension. We measured changes in the cerebral concentrations of oxidized CCO (Δ[oxCCO]), oxyhemoglobin (Δ[HbO 2 ]), and deoxyhemoglo-bin (Δ[HHb] ) using broadband near-IR spectroscopy (NIRS), and estimated changes in cerebral oxygen delivery (ecDO 2 ) using pulse oximetry and transcranial Doppler ultrasonography. Results are presented as median (interquartile range). At the nadir of hypoxemia ecDO 2 decreased by 9.2 (5.4 to 12.1)% (p < 0.0001), Δ[oxCCO] decreased by 0.24 (0.06 to 0.28) micromoles/l (p < 0.01), total hemoglobin concentration increased by 2.83 (2.27 to 4.46) micromoles/l (p < 0.0001), and change in hemoglobin difference concentration (Δ[Hbdiff]=Δ[HbO 2 ]-Δ[HHb] ) decreased by 12.72 (11.32 to 16.34) micromoles/l (p < 0.0001 ). Change in ecDO 2 correlated with Δ[oxCCO] (r=0.78, p < 0.001 ), but not with either change in total hemoglobin concentration or Δ[Hbdiff]. This is the first description of cerebral Δ[oxCCO] during hypoxemia in healthy adults. Studies are ongoing to investigate the clinical relevance of this signal in patients with traumatic brain injury. © 2007 Society of Photo-Optical Instrumentation Engineers.