Spatial Variation of the Local Tissue Oxygen Diffusion Coefficient Measured in situ in the Cat Retina and Cornea
Precise knowledge of the oxygen diffusion coefficient (D) in tissue is essential for the analysis of oxygen transport. The PO2 profile in a tissue can be measured with a deeply recessed (L/d > 5), Polarographic microelectrode (Linsenmeier, 1986; Haugh et al., 1990). By contrast, one with a shallow recess (L/d < 1) is affected by D in the tissue. It is possible to utilize this feature to determine the tissue D from the polarization transient when the electrode is turned on (i.e., the imposed voltage is changed). The faster the approach to steady state, the larger the value of D must be. Previous attempts to utilize a microelectrode turn-on transient to give local values of D in tissue (Erdmann and Krell, 1976; Buerk, 1980; Buerk and Goldstick, 1990) were plagued by the problem that initially the extremely large current saturated the amplifier. In the present study, the amplifier saturation was eliminated by open-circuiting the amplifier for a few ms initially. All of the data recorded after the initial delay, including those at very early times, were used for the calculation of D by a nonlinear regression analysis. Apparently there have been no reliable previous measurements of D in the mammalian retina or cornea in situ. The usual previous approach has been to make the measurement on a slice of excised tissue in vitro. The measurements in the present study are therefore novel because they are local and made in situ in the intact tissue of a living animal.
KeywordsIsotonic Saline Nonlinear Regression Analysis Outer Retina Oxygen Diffusion Coefficient Tungsten Microelectrode
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