Wen, B., Urano, M., Humm, J. L., Seshan, V. E., Li, G. C. and Ling, C. C. Comparison of Helzel and OxyLite Systems in the Measurements of Tumor Partial Oxygen Pressure (pO₂). Radiat. Res. 168, 67–75 (2008).

It has been demonstrated in both experimental and human malignancies that hypoxic tumor cells are linked with aggressive disease phenotype. One of the methods to identify these cells is by direct physical measurement of tumor pO₂. This study compared pO₂ values measured with two systems, the Helzel Hypoximeter (successor of the polarographic Eppendorf electrode) and the Oxford-Optronix OxyLite (fiber-optic probe), in R3327-AT and R3327-AT/tkeGFP tumors. Partial oxygen pressure was measured in individual tumors with either system or in the same tumor with both systems. The similarities and discrepancies in pO₂ measurements between the two systems were also investigated when tumor-bearing animals were breathing pure oxygen. Our data showed a considerable heterogeneity in pO₂ values in each tumor using both the Helzel and OxyLite systems. Similar results were obtained with both systems for the mean and median pO₂ values, and the distributions of pO₂ values within the interval 0 < pO₂ < 40 mmHg (the range important for defining tumor hypoxia) were found to be statistically equivalent. However, the frequencies of high pO₂ values (>40 mmHg) and zero values measured by the two systems were statistically significantly different.