Theoretical simulation of oxygen tension measurement in tissues using a microelectrode: I. The response function of the electrode

The aim of this article is to determine the correlation between the actual oxygen distribution in tissues and the distribution of oxygen measured by m icroelectrodes, This correlation is determined by the response function of the electrode, which depends on the oxygen consumed by the electrode. In ti ssue it is necessary to consider the gradients resulting from cellular resp iration. A computer program has been used to simulate the vascular structur e of various tissues and also the measurements of oxygen tension using a po larographic electrode. The electrode absorption process is described using a theoretical model. The gradient of oxygen in tissue is described by a mat hematical model that takes into consideration both diffusion and cellular c onsumption of oxygen. We have compared the results obtained using the respo nse function of the electrode and some simplifications of it. The results o f these comparisons show that there are some differences in the 'observed' distributions of the oxygen tension in tissues predicted using different fo rmulae for the electrode response function. Also, there are considerable di fferences between the input oxygen distribution and the measured values in all cases. All the results of the simulations of the oxygen tension 'observ ed' by a 12 mum polarographic electrode, using different response functions of the electrode, show that the electrode averages the values from many ce lls. Care should be taken in using a simplification for the response functi on of the electrode, especially if the results are going to be used as inpu t values in modelling the tumour response to new treatments and/or as a bas is of selecting patients for treatments. A computer simulation of measureme nt of oxygen tensions in regions of steep pO(2) gradients shows that extrem ely high and extremely low pO(2) values will not be detected.