Regional cerebrovascular oxygen saturation measured by optical spectroscopy in humans.

Abstract

Regional cerebrovascular oxygen saturation, a quantitative measure of hemoglobin saturation in the combined arterial, venous, and microcirculatory compartments of the brain, can be measured noninvasively with near infrared spectroscopy. We assessed the sensitivity of this aggregate saturation to cerebral hypoxia during transient cerebral hypoxic hypoxia in seven human subjects. Regional cerebrovascular oxygen saturation measured over the middle frontal gyms and analog electroencephalogram were recorded. We compared the time to achieve two end points: the earliest paroxysmal burst of theta-delta background slowing and a cerebrovascular oxygen saturation of <55%. Saturation fell below 55% prior to the electroencephalographic change (/?<0.05). In a related effort, we also compared spectroscopically measured regional cerebrovascular oxygen saturation with an estimate of this value calculated from arterial and cerebral mixed venous saturation in nine patients. A positive linear relation (n=68, /f=0.55, s=4.2) was noted. (Stroke 1991^2:596-602)

Global Cerebral Oxidative Metabolism during Hypercapnia and Hypocapnia in Humans: Implications for BOLD fMRI

“…Our measurement of cerebral venous oxygenation (Y) by T 2 -based magnetic resonance oximetry was in good agreement with jugular bulb measurements (McCormick et al, 1991), and covaried with CBF. Moreover, the comparability between PASL and PC measurements of the CBF response to graded hypercapnia and hypocapnia supports the use of PASL for measuring whole-brain CBF changes.…”

Near-Infrared Spectroscopy

“…Cerebral NIRS devices measure mean tissue oxygen saturation and, as such, reflect hemoglobin saturation in venous, capillary, and arterial blood comprising the sampling volume. For cerebral cortex, average tissue hemoglobin is distributed in a proportion of 70% venous and 30% arterial (McCormick et al, 1991), based on correlations between position emission tomography (PET) and NIRS (Ohmae et al, 2006). However, clinical studies have demonstrated that there can be considerable biological variation in individual cerebral arterial/venous (A/V) ratios between patients, further underscoring that the use of a fixed ratio can produce significant divergence from actual in vivo tissue oxygen saturation, thus confounding even 'absolute' measures of changes in cerebral oxygenation (Watzman et al, 2000).…”

Le monitorage de l’oxygénation cérébrale

“…Additionally, by using both a "shallow" and a "deep" sensor configuration, the effect of extracranial tissue can be effectively neutralized by subtraction techniques. 22 In this application, because of difficulties in quantitating absorption of individual spectra, the ratio of haemoglobin to oxyhaemoglobin, calculated as cerebrovascular oxygen saturation, is determined. The accuracy of this estimate is influenced by the partitioning of cerebral blood volume into arterial, venous and capillary compartments.…”

“…In addition, with the usual percutaneous sensor placement over the region of the frontal lobe, the volume of brain tissue sampled is approximately 1.0-1.5 ml at a depth of 8 to 12 mm, thus the resultant SrO2 is highly localized. 22 This technique has been assessed both by using hypoxic challenge in volunteers, wherein SrO2 demonstrated earlier detection of hypoxia than did EEG, and by demonstrating good correlation of SrO2 with. jugular bulb saturation in head-injured patients.…”