Importance of mitochondrial PO2 in maximal O2 transport and utilization: A theoretical analysis

In previous calculations of how the O-2 transport system limits V-o2 max, it was reasonably assumed that mitochondrial P-o2 (Pm-o2) could be neglected (set to zero). However, in reality, Pm-o2 must exceed zero and the red cell to mitochondrion diffusion gradient may therefore be reduced, impairing diffusive transport of O-2 and V-o2 max. Accordingly, we investigated the influence of Pm-o2 on these calculations by coupling previously used equations for O-2 transport to one for mitochondrial respiration relating mitochondrial V-o2 to P-o2. This hyperbolic function, characterized by its P-50 and V-MAX, allowed Pm-o2 to become a model output (rather than set to zero as previously). Simulations using data from exercising normal subjects showed that at V-o2 max, Pm-o2 was usually <1 mm Hg, and that the effects on V(o2)max were minimal. However, when O-2 transport capacity exceeded mitochondrial V-MAX, or if P-50 were elevated, Pm-o2 often reached double digit values, thereby reducing the diffusion gradient and significantly decreasing V-o2 max. (C) 2013 Elsevier B.V. All rights reserved.