Fourier analysis of fluctuations of oxygen tension and blood flow in R3230Ac tumors and muscle in rats

Tumor hypoxia is a major barrier to tumor radiation therapy. Typically tumo r hypoxia occurs in two forms: chronic and acute. Although the existence of acute hypoxia has long been acknowledged, its temporal characteristics hav e never been directly measured and documented. In this study tumor Po-2, bl ood flow (BF), and arterial blood pressure (BP) were measured simultaneousl y in nine Fischer 344 rats bearing R3230Ac rat mammary adenocarcinomas in t he subcutis of the left hindleg. We measured Po-2 at a single location for 36-125 min using recessed-tip oxygen microelectrodes. Simultaneously, we me asured tumor BF at two sites within the tumor using laser-Doppler flowmetry (LDF). Similar recordings were made in the quadriceps muscle of seven non- tumor-bearing rats. The Po-2, tumor BF, and BP records were subjected to Fo urier analysis. Po-2 and BF showed low-frequency fluctuations (<2 cycles/mi n) in both tumor and muscle, but the magnitude of the changes in tumor was greater. Tumor BF showed more activity at low frequencies than muscle BF, a nd the magnitude tended to be greater. No strong correlations were found be tween Po-2 and BF power spectra for either tumor or muscle or between the f requency patterns of BP and tumor Po-2 spectra. These results quantitativel y demonstrate, for the first time, that BF and Po-2 fluctuate at very low f requencies in tumors. In addition to having biological significance for tum or therapy, these fluctuations may have the potential to alter tumor cell b ehavior via induction of hypoxia reoxygenation injury and/or altered gene e xpression.