A New, Water Soluble, Phosphor for Oxygen Measurements in Vivo

Abstract

Oxygen dependent quenching of phosphorescence is an optical method for non-invasive measurements of oxygen in the microvasculature of tissue (see ^3-7,10,11). it is unique among the oxygen measuring methods in that it is noninvasive and yet provides quantitative measurements with an excellent temporal resolution (milliseconds). Development of the technology has been rapid, and the phosphors available for oxygen measurements has been rapidly expanding. The phosphor which has been in greatest use is Pd-meso-tetra-(4carboxyphenyl) porphine and this has been thoroughly calibrated2. The solubility of this phosphor in aqueous solutions at physiological pH is, however, low. In order to improve the aqueous solubility and to provide a phosphor environment which optimized for physiological measurements, the phosphor is dissolved in solutions containing high concentrations of serum albumin. Albumin binds the phosphor, providing both the necessary solubility in biological media and restricting the access of oxygen to the excited state phosphor. The latter is useful in that the restricted access to oxygen results in the the phosphorescence lifetime changing from near 650 μisec at zero oxygen to about 16 μsec at air saturation (38 °C). On the other hand, dissolving the phosphor in solutions containing high concentrations of albumin means that if these solutions are then injected into the blood of an animal, the animal is exposed to relatively large amounts of foreign protein as well as any endotoxin and other contaminants in the albumin. The necessity for injecting a foreign protein can be avoided by removing blood from the animal, preparing serum, dissolving the phosphor to the serum, and then reinjecting the serum with phosphor. Using a water soluble phosphor would allow this rather complicated procedure to be avoided, since the phosphor could be dissolved in physiological saline and the resulting solution injected.