Sharan M, Vovenko EP, Vadapalli A, Popel AS, Pittman RNExperimental and theoretical studies of oxygen gradients in rat pial microvessels. J Cereb Blood Flow Metab 28:1597-1604

Centre for Atmospheric Sciences, Indian Institute of Technology, Delhi, India.
Journal of cerebral blood flow and metabolism: official journal of the International Society of Cerebral Blood Flow and Metabolism (Impact Factor: 5.41). 05/2008; 28(9):1597-604. DOI: 10.1038/jcbfm.2008.51
Source: PubMed


Using modified oxygen needle microelectrodes and intravital videomicroscopy, measurements were made of tissue oxygen tension (PO(2)) profiles near cortical arterioles and transmural PO(2) gradients in the pial arterioles of the rat. Under control conditions, the transmural PO(2) gradient averaged 1.17+/-0.06 mm Hg/microm (mean+/-s.e., n=40). Local arteriolar dilation resulted in a marked decrease in the transmural PO(2) gradient to 0.68+/-0.04 mm Hg/microm (P<0.001, n=38). The major finding of this study is a dependence of the transmural PO(2) gradient on the vascular tone of the pial arterioles. Using a model of oxygen transport in an arteriole and experimental PO(2) profiles, values of radial perivascular and intravascular O(2) fluxes were estimated. Our theoretical estimates show that oxygen flux values at the outer surface of the arteriolar wall are approximately 10(-5) mL O(2)/cm(2) per sec, independent of the values of the arteriolar wall O(2) consumption within a wide range of consumption values. This also means that PO(2) transmural gradients for cerebral arterioles are within the limits of 1 to 2 mm Hg/microm. The data lead to the conclusion that O(2) consumption of the arteriolar wall is within the range for the surrounding tissue and O(2) consumption of the endothelial layer appears to have no substantial impact on the transmural PO(2) gradient.

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    • "Such measurements have provided an invaluable insight into tissue oxygen dynamics in cerebral (Thompson et al., 2003; Viswanathan and Freeman, 2007) and cerebellar cortex (Offenhauser et al., 2005) but they have also demonstrated a significant degree of variability, which has been attributed to possible differences in electrode position relative to the vascular oxygen sources (Erecinska and Silver, 2001; Masamoto et al., 2003). Oxygen electrodes have also been used to map intravascular oxygenation on the cortical surface (Vovenko, 1999; Sharan et al., 2008; Vazquez et al., 2010). While these and other studies (Vanzetta and Grinvald, 1999; Ances et al., 2001; Yaseen et al., 2009) have established the Corresponding author: Anna Devor, Departments of Neurosciences and Radiology, University of California San Diego, Tel: 858-353-3315 Fax: 858-534-1078, "
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    ABSTRACT: In vivo imaging of cerebral tissue oxygenation is important in defining healthy physiology and pathological departures associated with cerebral disease. We used a recently developed two-photon microscopy method, based on a novel phosphorescent nanoprobe, to image tissue oxygenation in the rat primary sensory cortex in response to sensory stimulation. Our measurements showed that a stimulus-evoked increase in tissue pO₂ depended on the baseline pO₂ level. In particular, during sustained stimulation, the steady-state pO₂ at low-baseline locations remained at the baseline, despite large pO₂ increases elsewhere. In contrast to the steady state, where pO₂ never decreased below the baseline, transient decreases occurred during the "initial dip" and "poststimulus undershoot." These results suggest that the increase in blood oxygenation during the hemodynamic response, which has been perceived as a paradox, may serve to prevent a sustained oxygenation drop at tissue locations that are remote from the vascular feeding sources.
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    • "in capillaries (Duling et al., 1979; Sharan et al., 2008). This gradient was observed to take tens of micrometers to equilibrate with the average tissue oxygen tension. "
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    • "Another Clark-type sensor was then placed on the superior surface of a selected artery supplying blood to the active area. Preliminary testing of the spatial sensitivity of the probe for intra-luminal vs surface recordings determined that this placement is sensitive to the vessel oxygen tension, in agreement with similar studies (Vovenko, 1999; Sharan, et al, 2008). Three positions were sampled along the selected artery: one just prior to its intra-cortical penetrating point (referred to as small artery, SmArt or SA) and two upstream parent branches (referred to as medium and large artery, or MedArt and LarArt, or MA and LA, respectively). "
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