Spatial oxygenation profiles in tumors during normo- and hyperbaric hyperoxia

Background Inspiratory hyperoxia reduces tumor hypoxia, which is responsible for limited radiosensitivity of tumors. However, very little is known about the heterogeneity of intratumoral oxygenation during this supportive treatment. The study analyzes whether local hypoxia is still present during normobaric and hyperbaric inspiratory hyperoxia and whether the addition of CO2 to the inspiratory gas affects the spatial pO(2) distribution. Material and methods Tumor oxygenation of experimental DS-sarcomas in rats was assessed by polarographic needle electrodes at 1 and 2 atm (bar) environmental pressure during pure O-2 or carbogen (95 % O-2 + 5 % CO2) breathing. Up to 320 individual pO(2) measurements were performed in a strictly oriented grid resulting in an oxygenation profile in a horizontal tumor layer. Results In the experimental tumors used the oxygenation showed pronounced heterogeneities with closely adjacent hypoxic and oxygenated regions. This heterogeneity was still visible under normobaric hyperoxia where large confluent hypoxic regions were detectable. At 1 atm, the addition of CO2 improved tumor oxygenation significantly (at least in large tumors). At 2 atm, only very small local regions of hypoxia were detected. However, under this condition hypercapnia had no impact on tumor oxygenation. Conclusions The data show that even under hyperbaric hyperoxia, hypoxic regions are detectable despite the average pO(2) increased by a factor of 100. The results also clearly indicate that the oxygenation pattern improves disproportionally with increasing environmental pressure.