Comparison of EPR oximetry and Eppendorf polarographic electrode assessments of rat brain PtO₂

Abstract

EPR oximetry is a promising, relatively non-invasive method for monitoring the partial pressure of oxygen in tissue (PtO2) that has proved useful in following changes under various physiologic and pathophysiologic conditions. Optimal utilization of the method will be facilitated by systematic comparisons with other available methods. Here we report on the absolute values of rat brain PtO2 using EPR and the more widely used Eppendorf polarographic microelectrode system in the same brain. EPR used an L-band (1.2 GHz) spectrometer and implanted lithium phthalocyanine (LiPc) as the oxygen-sensitive paramagnetic material. Eppendorf measurements were made by a needle probe moved vertically through the cortex at 0.5 mm intervals in three tracks including one adjacent to the location of the LiPc. Several conclusions were drawn, including, (1) the average PtO2 measured by the two methods was similar but EPR reported a significantly higher average PtO2, (2) there was poor correlation between the values in the same animal on the same side of the brain, (3) the Eppendorf reported a larger range of values and (4) the heterogeneity of oxygen levels in the brain and the areas sampled by the two methods provide an adequate explanation for the observed differences.

Repetitive Tissue pO2 Measurements by Electron Paramagnetic Resonance Oximetry: Current Status and Future Potential for Experimental and Clinical Studies

“…Using an appropriate calibration curve, the line width of the EPR signal provides a sensitive measurement of tissue oxygen. This technique has been used to study the tissue pO 2 pO 2 in a wide range of experimental systems, including muscle (18,23), heart (11,16,17), brain (26,27,28,41,62), kidney (33,34), liver (35,44,64), skin (1) and tumors (29,30,47,49,50).…”

“…Tissue pO 2 reported by EPR oximetry has been compared directly with the Eppendorf system in the same animals (49). The average pO 2 values in the rat brain cortex measured by the two methods were similar, but the EPR oximetry method reported a statistically significantly higher average pO 2 .…”

In vivo electron paramagnetic resonance oximetry and applications in the brain

“…Even so, the microelectrodes and polarography do offer several disadvantages including invasiveness, consumption of O 2 (in most cases), and the inability to make repetitive measurements over prolonged time period ( e.g ., days). However, advancements in the design of commercially available microelectrodes have improved the use of this technique8102930 and this method offers several advantages, including highly quantitative direct pO 2 measurements. Moreover, while polarography normally allows for point measurements, recent improvements in planar polarographic electrodes may allow for 2D mapping of tissue pO 2 11 so that the technique is not superseded by methods which can provide images.…”

Real-time monitoring of ischemic and contralateral brain pO2 during stroke by variable length multisite resonators

“…Several methods have been developed to measure pO 2 , including the Clark electrode, optical methods based on fluorescence quenching or phosphorescence quenching, MRI, PET and EPR oximetry (3–8). Each of these methods has specific advantages as well as limitations, especially for repeated measurement of cerebral pO 2 (5).…”

“…Each of these methods has specific advantages as well as limitations, especially for repeated measurement of cerebral pO 2 (5). Clark electrodes cause trauma when inserted into the brain and potentially affect the pO 2 measurements (3). Optical techniques have a very limited depth of measurement (< 2 mm) when made non-invasively from the surface.…”