Basic aspects

The last step of the oxygen cascade - transportation of O2 into the cell -is achieved by convection, i.e. DO2 (local circulation), and by passive diffusion. The actual tissue oxygen pressure is the result of equilibrium between the amount of oxygen extracted by the individual tissue and the amount of oxygen consumed by the cells48. The variables finally defining the level of tissue oxygen pressure are as follows:

a) regional energy expenditure according to tissue metabolism;

b) features of the cardiovascular system and microvascular perfusion;

c) the oxygen-carrying capacity of the blood;

d) features of diffusion from the capillaries to the mitochondria within the target tissue.

Several mathematical models49,50 have been established for the description of their interactions and performance.

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