Evaluation of PO(2) profiles to describe the oxygen pressure field within the tissue.

Oxygen transport within the tissue occurs by diffusion and produces an oxygen pressure field. To describe its heterogeneity histograms of local PO(2) values are used. PO(2) profiles measured with small polarographic microelectrodes demonstrate that a large heterogeneity of the amplitudes of local PO(2) changes (Delta PO(2)/distance) exists. Therefore, we investigated whether the amplitudes of local PO(2) changes can be used to obtain additional information about the state of oxygen supply. Six PO(2) profiles in the renal cortex of the dog were evaluated. The frequency histograms of the local PO(2) values showed a normal oxygen supply of the kidneys. To analyze the heterogeneity of the amplitudes of the local PO(2) changes every 10 microm the (Delta PO(2)/distance) values were determined. Most of the amplitudes steps are in the range of +/-10 torr. The frequency histogram of the amplitudes steps shows a symmetric form: 100% are between -35 and +49 torr, 90% between -12 and +11 torr. Changes of the amplitude histogram occur if the distances between the selected adjacent points are varied. At distances larger than 100 microm the amplitude histograms became disintegrated. Interestingly, the local PO(2) histograms remained practically unchanged. Therefore we conclude, that by this measuring and evaluation technique histograms of the (Delta PO(2)/microm) values are obtained by which the state of oxygen supply of local structures can be monitored, probably of the microcirculatory unit of capillary oxygen supply. The results demonstrate a well-regulated oxygen pressure field within the kidney. Similar results were obtained from PO(2) profiles measured in the brain cortex (Delta PO(2)/50 microm).