In Vivo Application PD-Porphine for Measurement of Oxygen Concentrations in the Gut

Abstract

Adequate measurement of microcirculatory tissue oxygen concentrations in vivo is essential for further understanding of determinants of cellular respiration under normal and pathological conditions. Because the oxygenation of tissue primarily takes place in the microcirculation, techniques need to be developed which are applicable in the arterioles, capillaries and venules in vivo. Conventionally such types of measurements have been made by use of oxygen electrodes and spectrophotometry of the haemoglobin molecule. Spectrop-hotometrically measured changes in the absorption spectrum of the haemoglobin molecule determines the ratio of the amount of oxy- and deoxy-hemoglobin. This method gives a qualitative measure of the amount of available oxygen but cannot give quantitative information about the amount of dissolved oxygen in the plasma. Oxygen electrodes on the other hand provide quantitative measurements but are too big to measure at the microcirculatory level and if inserted into the tissue disrupt the microcirculatory environment. These constraints have led to the development of alternative methods. One of the most promising techniques in this respect has been the use of oxygen dependent quenching of fluorescent and phosphorescent dyes (Sanders 1995, Wilson 1991, Sinaasappel and Ince 1996). In such measurements the decay time of either fluorescence or phosphorescence following excitation by a light pulse is oxygen dependent and described by the Stern-Volmer relation. This time resolved technique is very suitable for use in vivo because many of the problems encountered with intensity measurements, such as the absorption and scattering of light by tissue components, are eliminated.