Interpretation of Phosphorescence Quenching Measurements Made in the Presence of Oxygen Gradients

Abstract

The quenching of phosphorescence by molecular oxygen has proved to be a useful, noninvasive technique for determining oxygen tension (PO₂) or dissolved oxygen concentration ([O₂]) in blood vessels and tissues (Vanderkooi et al., 1987; Shonat et al., 1992 & 1995; Torres Filho and Intaglietta, 1993; Torres Filho et al., 1994 & 1996; Kerger et al., 1995; Zheng et al., 1996). The technique can be calibrated under controlled conditions in vitro (Sinaasappel and Ince, 1996), and, for uniformly distributed free oxygen, PO₂ is related to phosphorescence lifetime by the Stern-Volmer equation: l/τ=l/τ₀ + k_qPO₂ (1) where τ is the lifetime in the presence of oxygen, τ₀ is the lifetime in the absence of oxygen, and k_q is the quenching coefficient (which includes the solubility of oxygen in the calibration medium). Under the condition of uniform PO₂, the time course of the phosphorescence decay is monoexponential with lifetime τ.