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1 Department of Physiology, University of Amsterdam, Academic Medical Center, Amsterdam, The Netherlands; Department of Anesthesiology and Critical Care, University Hospital Tuebingen, Tuebingen, Germany
2 Department of Physiology, University of Amsterdam, Academic Medical Center, Amsterdam, The Netherlands
* To whom correspondence should be addressed. E-mail: C.Ince{at}amc.uva.nl.
This study presents a dual-wavelength phosphorimeter developed to measure microvascular PO2 (µPO2) in different depths in tissue and demonstrates its use in rat kidney. The used phosphorescent dye is Oxyphor G2 with excitation bands at 440 and 632 nm. The broad spectral gap between the excitation bands combined with a relatively low light absorption of 632 nm light by tissue results in a marked difference in penetration depths of both excitation wavelengths. In rat kidney we determine the catchments depth of the 440 nm excitation to be 700 µm while the catchments depth of 632 nm is as much as 4 mm. Therefore the measurements differentiate between cortex and outer medulla respectively. In vitro no difference in PO2 readings between both channels was found. On the rat kidney in vivo the measured cortical µPO2 was on average 20 mmHg higher than the medullary µPO2 over a wide PO2 range induced by variations in FiO2. Examples provided from endotoxemia and resuscitation show differences in responses of mean cortical and medullary PO2 readings as well as in the shape of the PO2 histograms. It can be concluded that oxygen-dependent quenching of phosphorescence of Oxyphor G2 allows quantitative measurement of µPO2 non-invasively in two different depths in vivo. Oxygen levels measured by this technique in the rat renal cortex and outer medulla are consistent with previous published values detected by Clark-type O2-electrodes. Dual-wavelength phosphorimetry is excellently suited for monitoring µPO2 changes in two different anatomical layers under patho-physiological conditions with the characteristics of providing oxygen histograms from two depths and having a penetration depth of several millimeters.
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