Method for the measurement of oxygen concentration levels by the steady-state determination of fluorescence lifetime

Abstract

Methods are described for the in vivo topographic determination of tissue and bodily fluid oxygen concentration or PO.sub.2 within an imaged tissue, as well as a method for measuring blood or bodily fluid PO.sub.2 with a fiber optic catheter. In the first method, a lipid soluble, biocompatible fluorescent probe substance is administered to an animal body and accumulates within the lipid bilayers of its tissue cells. In the second method, the fluorescent probe substance is conjugated to a large molecular mass protein which causes it to be retained within a bodily fluid such as blood. In the third method describing a catheter design, in which PO.sub.2 is measured at the catheter tip, the tip contains the fluorescent probe substance dissolved in a viscous nonpolar solvent. In all methods described, a fluorescent probe substance is preferred whose fluorescence lifetime is quenched by molecular oxygen, and oxygen concentration or PO.sub.2 is determined by measuring the fluorescence anisotropy of the fluorescent probe substance. The bodily fluid or tissue containing the biocompatible fluorescent probe substance, or the fluorescent probe substance in a nonpolar solvent within a catheter tip, is irradiated with continuous linearly polarized ultraviolet light at a wavelength strongly absorbed by the fluorophore. The emitted fluorescence is resolved into its vector components parallel and perpendicular to the plane of polarization of the excitation light, thereby permitting the calculation of the fluorescence anisotropy of the irradiated specimen. Tissue and/or bodily fluid PO.sub.2 of the imaged specimen, or the PO.sub.2 of a fluid at the tip of a sealed catheter, is determined by applying a mathematical function which relates the fluorescence anisotropy of an O.sub.2 -quenchable fluorophore to oxygen concentration or partial pressure.

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