Abstract
Adequate measurement of microcirculatory oxygen (O2) concentrations in vivo is essential for further understanding of determinants of cellular respiration under
normal and pathological conditions. Conventionally, such types of measurements have
been made by the use of O2 electrodes and spectrophotometry of the hemoglobin (Hb) molecule. Spectrophotometrically
measured changes in the absorption spectrum of the Hb molecule determine the ratio
of the amount of oxyhemoglobin and deoxyhemoglobin. Oxygen electrodes 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 O2-dependent quenching of phosphorescent dyes. In such measurements the decay time of
phosphorescence following excitation by a light pulse is O2 dependent. This time-resolved technique could be 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. O2-dependent quenching of phosphorescence has been used for the determination of O2 concentrations in vitro. The recent introduction of palladium (Pd)-porphyrin phosphorescent dyes allows quantitative
in vivo measurements and could be developed clinically as a valuable technique for continuous
measurement of microvascular O2 partial pressure at multiple locations.
Key Words:
O2 electrodes - phosphorescence - NADH fluorescence - tonometry - spectrophotometry
- nuclear magnetic resonance - O2 delivery - O2 uptake
