Analysis of oxygen transport to the brain when two or more parameters are affected simultaneously.

We composed a model, combining oxygen transport system from blood to tissue with the oxygen consumption system at the tissue. The aim of this study is to apply it to the brain tissue under conditions when two or more oxygen transport parameters are affected simultaneously. The following values were assumed. Critical tissue P(O)(2) (Pcrit(O)(2)) 2 mmHg; oxygen consumption above this level 3 ml.min(-1).100 g(-1); diffusion coefficient from blood vessel to tissue (Dvt) 0.2 ml.min(-1).mmHg(-1).100 g(-1); cerebral bloow flow (CBF) 50 ml.min(-1).100 g(-1); hemoglobin 15 g.100 ml(-1). The Hill equation was used for oxygen dissociation curve with n of 2.7 and P(50) of 27.0 mmHg. The changes of oxygen consumption of the brain (V(O)(2)) were analyzed when 2 or more of 5 parameters, Pa(O)(2), CBF, Dvt, P(50) and hemoglobin decreased simultaneously from their respective normal values. As the number of parameters affected increased, the level at which oxygen consumption begins to be affected became higher. With all five parameters combined, a reduction down to 78 per cent of normal resulted in tissue hypoxia. We conclude that the oxygen consumption of the brain is fairly resistant when only one parameter is affected, but it becomes increasingly vulnerable when several parameters are affected simultaneously. A clinically important finding is that the brain is particularly vulnerable to a combination of hypocapnia and a decreased level of 2,3DPG.