Microvascular partial oxygen pressure (PO₂) data measured with the quenched phosphorescence of palladium-porphyrin (Pd-porphyrin) with the use of optical fibers have provided new insight into the behavior of the microvascular oxygenation in models of shock. However, the actual microcirculatory compartment measured by this fiber technique has not yet been demonstrated. The purpose of this study was to investigate whether the PO₂ of the intestines, as measured using a fiber phosphorometer, reflects the microvascular compartment. To this end, a new intravital phosphorometer with an improved sensitivity to high-PO₂ levels (up to 180 mmHg) was developed and validated. With this setup, PO₂ values were measured at different inspired oxygen fractions (15, 25, and 50% oxygen) in first-order arterioles, capillaries, and venules of the ileum of rats. Simultaneously, the PO₂ was measured with an optical fiber attached to another phosphorometer. PO₂ measurements with the fiber phosphorometer show excellent correlation with the PO₂ in the capillaries and first-order venule vessels (r² = 0.94, slope 0.99). We therefore conclude that values measured with the fiber phosphorometer correlate with the capillary and venular PO₂.

intravital microscopy; palladium-porphyrin; phosphorescence quenching

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